# Struct alloc::vec::Vec

1.0.0 · source ·

    pub struct Vec<T, A: Allocator = Global, FH: FailureHandling = DefaultFailureHandling> { /* private fields */ }

Expand description

A contiguous growable array type, written as `Vec<T>`, short for ‘vector’.

## Examples

    let mut vec = Vec::new();
    vec.push(1);
    vec.push(2);

    assert_eq!(vec.len(), 2);
    assert_eq!(vec[0], 1);

    assert_eq!(vec.pop(), Some(2));
    assert_eq!(vec.len(), 1);

    vec[0] = 7;
    assert_eq!(vec[0], 7);

    vec.extend([1, 2, 3]);

    for x in &vec {
        println!("{x}");
    }
    assert_eq!(vec, [7, 1, 2, 3]);

Run

The `vec!` macro is provided for convenient initialization:

    let mut vec1 = vec![1, 2, 3];
    vec1.push(4);
    let vec2 = Vec::from([1, 2, 3, 4]);
    assert_eq!(vec1, vec2);

Run

It can also initialize each element of a `Vec<T>` with a given value. This may be more efficient than performing allocation and initialization in separate steps, especially when initializing a vector of zeros:

    let vec = vec![0; 5];
    assert_eq!(vec, [0, 0, 0, 0, 0]);

    // The following is equivalent, but potentially slower:
    let mut vec = Vec::with_capacity(5);
    vec.resize(5, 0);
    assert_eq!(vec, [0, 0, 0, 0, 0]);

Run

For more information, see Capacity and Reallocation.

Use a `Vec<T>` as an efficient stack:

    let mut stack = Vec::new();

    stack.push(1);
    stack.push(2);
    stack.push(3);

    while let Some(top) = stack.pop() {
        // Prints 3, 2, 1
        println!("{top}");
    }

Run

## Indexing

The `Vec` type allows access to values by index, because it implements the `Index` trait. An example will be more explicit:

    let v = vec![0, 2, 4, 6];
    println!("{}", v[1]); // it will display '2'

Run

However be careful: if you try to access an index which isn’t in the `Vec`, your software will panic! You cannot do this:

ⓘ

    let v = vec![0, 2, 4, 6];
    println!("{}", v[6]); // it will panic!

Run

Use `get` and `get_mut` if you want to check whether the index is in the `Vec`.

## Slicing

A `Vec` can be mutable. On the other hand, slices are read-only objects. To get a slice, use `&`. Example:

    fn read_slice(slice: &[usize]) {
        // ...
    }

    let v = vec![0, 1];
    read_slice(&v);

    // ... and that's all!
    // you can also do it like this:
    let u: &[usize] = &v;
    // or like this:
    let u: &[_] = &v;

Run

In Rust, it’s more common to pass slices as arguments rather than vectors when you just want to provide read access. The same goes for `String` and `&str`.

## Capacity and reallocation

The capacity of a vector is the amount of space allocated for any future elements that will be added onto the vector. This is not to be confused with the length of a vector, which specifies the number of actual elements within the vector. If a vector’s length exceeds its capacity, its capacity will automatically be increased, but its elements will have to be reallocated.

For example, a vector with capacity 10 and length 0 would be an empty vector with space for 10 more elements. Pushing 10 or fewer elements onto the vector will not change its capacity or cause reallocation to occur. However, if the vector’s length is increased to 11, it will have to reallocate, which can be slow. For this reason, it is recommended to use `Vec::with_capacity` whenever possible to specify how big the vector is expected to get.

## Guarantees

Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees about its design. This ensures that it’s as low-overhead as possible in the general case, and can be correctly manipulated in primitive ways by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`. If additional type parameters are added (e.g., to support custom allocators), overriding their defaults may change the behavior.

Most fundamentally, `Vec` is and always will be a (pointer, capacity, length) triplet. No more, no less. The order of these fields is completely unspecified, and you should use the appropriate methods to modify these. The pointer will never be null, so this type is null-pointer-optimized.

However, the pointer might not actually point to allocated memory. In particular, if you construct a `Vec` with capacity 0 via `Vec::new`, `vec![]`, `Vec::with_capacity(0)`, or by calling `shrink_to_fit` on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized types inside a `Vec`, it will not allocate space for them. Note that in this case the `Vec` might not report a `capacity` of 0. `Vec` will allocate if and only if `mem::size_of::<T>() * capacity() > 0`. In general, `Vec`’s allocation details are very subtle — if you intend to allocate memory using a `Vec` and use it for something else (either to pass to unsafe code, or to build your own memory-backed collection), be sure to deallocate this memory by using `from_raw_parts` to recover the `Vec` and then dropping it.

If a `Vec` has allocated memory, then the memory it points to is on the heap (as defined by the allocator Rust is configured to use by default), and its pointer points to `len` initialized, contiguous elements in order (what you would see if you coerced it to a slice), followed by `capacity - len` logically uninitialized, contiguous elements.

A vector containing the elements `'a'` and `'b'` with capacity 4 can be visualized as below. The top part is the `Vec` struct, it contains a pointer to the head of the allocation in the heap, length and capacity. The bottom part is the allocation on the heap, a contiguous memory block.

                ptr      len  capacity
           +--------+--------+--------+
           | 0x0123 |      2 |      4 |
           +--------+--------+--------+
                |
                v
    Heap   +--------+--------+--------+--------+
           |    'a' |    'b' | uninit | uninit |
           +--------+--------+--------+--------+

- uninit represents memory that is not initialized, see `MaybeUninit`.
- Note: the ABI is not stable and `Vec` makes no guarantees about its memory layout (including the order of fields).

`Vec` will never perform a “small optimization” where elements are actually stored on the stack for two reasons:

- It would make it more difficult for unsafe code to correctly manipulate a `Vec`. The contents of a `Vec` wouldn’t have a stable address if it were only moved, and it would be more difficult to determine if a `Vec` had actually allocated memory.

- It would penalize the general case, incurring an additional branch on every access.

`Vec` will never automatically shrink itself, even if completely empty. This ensures no unnecessary allocations or deallocations occur. Emptying a `Vec` and then filling it back up to the same `len` should incur no calls to the allocator. If you wish to free up unused memory, use `shrink_to_fit` or `shrink_to`.

`push` and `insert` will never (re)allocate if the reported capacity is sufficient. `push` and `insert` will (re)allocate if `len == capacity`. That is, the reported capacity is completely accurate, and can be relied on. It can even be used to manually free the memory allocated by a `Vec` if desired. Bulk insertion methods may reallocate, even when not necessary.

`Vec` does not guarantee any particular growth strategy when reallocating when full, nor when `reserve` is called. The current strategy is basic and it may prove desirable to use a non-constant growth factor. Whatever strategy is used will of course guarantee O(1) amortized `push`.

`vec![x; n]`, `vec![a, b, c, d]`, and `Vec::with_capacity(n)`, will all produce a `Vec` with exactly the requested capacity. If `len == capacity`, (as is the case for the `vec!` macro), then a `Vec<T>` can be converted to and from a `Box<[T]>` without reallocating or moving the elements.

`Vec` will not specifically overwrite any data that is removed from it, but also won’t specifically preserve it. Its uninitialized memory is scratch space that it may use however it wants. It will generally just do whatever is most efficient or otherwise easy to implement. Do not rely on removed data to be erased for security purposes. Even if you drop a `Vec`, its buffer may simply be reused by another allocation. Even if you zero a `Vec`’s memory first, that might not actually happen because the optimizer does not consider this a side-effect that must be preserved. There is one case which we will not break, however: using `unsafe` code to write to the excess capacity, and then increasing the length to match, is always valid.

Currently, `Vec` does not guarantee the order in which elements are dropped. The order has changed in the past and may change again.

## Implementations§

source§

### impl<T> Vec<T>

const: 1.39.0 · source

#### pub const fn new() -> Self

Constructs a new, empty `Vec<T>`.

The vector will not allocate until elements are pushed onto it.

##### Examples

    let mut vec: Vec<i32> = Vec::new();

Run
source

#### pub fn with_capacity(capacity: usize) -> Self

Constructs a new, empty `Vec<T>` with at least the specified capacity.

The vector will be able to hold at least `capacity` elements without reallocating. This method is allowed to allocate for more elements than `capacity`. If `capacity` is 0, the vector will not allocate.

It is important to note that although the returned vector has the minimum capacity specified, the vector will have a zero length. For an explanation of the difference between length and capacity, see Capacity and reallocation.

If it is important to know the exact allocated capacity of a `Vec`, always use the `capacity` method after construction.

For `Vec<T>` where `T` is a zero-sized type, there will be no allocation and the capacity will always be `usize::MAX`.

##### Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

##### Examples

    let mut vec = Vec::with_capacity(10);

    // The vector contains no items, even though it has capacity for more
    assert_eq!(vec.len(), 0);
    assert!(vec.capacity() >= 10);

    // These are all done without reallocating...
    for i in 0..10 {
        vec.push(i);
    }
    assert_eq!(vec.len(), 10);
    assert!(vec.capacity() >= 10);

    // ...but this may make the vector reallocate
    vec.push(11);
    assert_eq!(vec.len(), 11);
    assert!(vec.capacity() >= 11);

    // A vector of a zero-sized type will always over-allocate, since no
    // allocation is necessary
    let vec_units = Vec::<()>::with_capacity(10);
    assert_eq!(vec_units.capacity(), usize::MAX);

Run
source

#### pub unsafe fn from_raw_parts( ptr: *mut T, length: usize, capacity: usize ) -> Self

Creates a `Vec<T>` directly from a pointer, a capacity, and a length.

##### Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

- `ptr` must have been allocated using the global allocator, such as via the `alloc::alloc` function.
- `T` needs to have the same alignment as what `ptr` was allocated with. (`T` having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the `dealloc` requirement that memory must be allocated and deallocated with the same layout.)
- The size of `T` times the `capacity` (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, `dealloc` must be called with the same layout `size`.)
- `length` needs to be less than or equal to `capacity`.
- The first `length` values must be properly initialized values of type `T`.
- `capacity` needs to be the capacity that the pointer was allocated with.
- The allocated size in bytes must be no larger than `isize::MAX`. See the safety documentation of `pointer::offset`.

These requirements are always upheld by any `ptr` that has been allocated via `Vec<T>`. Other allocation sources are allowed if the invariants are upheld.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example it is normally not safe to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`, doing so is only safe if the array was initially allocated by a `Vec` or `String`. It’s also not safe to build one from a `Vec<u16>` and its length, because the allocator cares about the alignment, and these two types have different alignments. The buffer was allocated with alignment 2 (for `u16`), but after turning it into a `Vec<u8>` it’ll be deallocated with alignment 1. To avoid these issues, it is often preferable to do casting/transmuting using `slice::from_raw_parts` instead.

The ownership of `ptr` is effectively transferred to the `Vec<T>` which may then deallocate, reallocate or change the contents of memory pointed to by the pointer at will. Ensure that nothing else uses the pointer after calling this function.

##### Examples

    use std::ptr;
    use std::mem;

    let v = vec![1, 2, 3];

    // Prevent running `v`'s destructor so we are in complete control
    // of the allocation.
    let mut v = mem::ManuallyDrop::new(v);

    // Pull out the various important pieces of information about `v`
    let p = v.as_mut_ptr();
    let len = v.len();
    let cap = v.capacity();

    unsafe {
        // Overwrite memory with 4, 5, 6
        for i in 0..len {
            ptr::write(p.add(i), 4 + i);
        }

        // Put everything back together into a Vec
        let rebuilt = Vec::from_raw_parts(p, len, cap);
        assert_eq!(rebuilt, [4, 5, 6]);
    }

Run

Using memory that was allocated elsewhere:

    use std::alloc::{alloc, Layout};

    fn main() {
        let layout = Layout::array::<u32>(16).expect("overflow cannot happen");

        let vec = unsafe {
            let mem = alloc(layout).cast::<u32>();
            if mem.is_null() {
                return;
            }

            mem.write(1_000_000);

            Vec::from_raw_parts(mem, 1, 16)
        };

        assert_eq!(vec, &[1_000_000]);
        assert_eq!(vec.capacity(), 16);
    }

Run
source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub const fn new_in(alloc: A) -> Self

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new, empty `Vec<T, A>`.

The vector will not allocate until elements are pushed onto it.

##### Examples

    #![feature(allocator_api)]

    use std::alloc::System;

    let mut vec: Vec<i32, _> = Vec::new_in(System);

Run
source§

### impl<T, A: Allocator> Vec<T, A, Fatal>

source

#### pub fn with_capacity_in(capacity: usize, alloc: A) -> Self

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new, empty `Vec<T, A>` with at least the specified capacity with the provided allocator.

The vector will be able to hold at least `capacity` elements without reallocating. This method is allowed to allocate for more elements than `capacity`. If `capacity` is 0, the vector will not allocate.

It is important to note that although the returned vector has the minimum capacity specified, the vector will have a zero length. For an explanation of the difference between length and capacity, see Capacity and reallocation.

If it is important to know the exact allocated capacity of a `Vec`, always use the `capacity` method after construction.

For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation and the capacity will always be `usize::MAX`.

##### Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

##### Examples

    #![feature(allocator_api)]

    use std::alloc::System;

    let mut vec = Vec::with_capacity_in(10, System);

    // The vector contains no items, even though it has capacity for more
    assert_eq!(vec.len(), 0);
    assert!(vec.capacity() >= 10);

    // These are all done without reallocating...
    for i in 0..10 {
        vec.push(i);
    }
    assert_eq!(vec.len(), 10);
    assert!(vec.capacity() >= 10);

    // ...but this may make the vector reallocate
    vec.push(11);
    assert_eq!(vec.len(), 11);
    assert!(vec.capacity() >= 11);

    // A vector of a zero-sized type will always over-allocate, since no
    // allocation is necessary
    let vec_units = Vec::<(), System>::with_capacity_in(10, System);
    assert_eq!(vec_units.capacity(), usize::MAX);

Run
source§

### impl<T, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn try_with_capacity_in( capacity: usize, alloc: A ) -> Result<Self, TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Like the other `with_capacity_in`, but returns `Err` instead of panicking when allocation size exceeds `isize::MAX` or aborting on allocation failure.

source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub unsafe fn from_raw_parts_in( ptr: *mut T, length: usize, capacity: usize, alloc: A ) -> Self

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Creates a `Vec<T, A>` directly from a pointer, a capacity, a length, and an allocator.

##### Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

- `ptr` must be currently allocated via the given allocator `alloc`.
- `T` needs to have the same alignment as what `ptr` was allocated with. (`T` having a less strict alignment is not sufficient, the alignment really needs to be equal to satisfy the `dealloc` requirement that memory must be allocated and deallocated with the same layout.)
- The size of `T` times the `capacity` (ie. the allocated size in bytes) needs to be the same size as the pointer was allocated with. (Because similar to alignment, `dealloc` must be called with the same layout `size`.)
- `length` needs to be less than or equal to `capacity`.
- The first `length` values must be properly initialized values of type `T`.
- `capacity` needs to fit the layout size that the pointer was allocated with.
- The allocated size in bytes must be no larger than `isize::MAX`. See the safety documentation of `pointer::offset`.

These requirements are always upheld by any `ptr` that has been allocated via `Vec<T, A>`. Other allocation sources are allowed if the invariants are upheld.

Violating these may cause problems like corrupting the allocator’s internal data structures. For example it is not safe to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`. It’s also not safe to build one from a `Vec<u16>` and its length, because the allocator cares about the alignment, and these two types have different alignments. The buffer was allocated with alignment 2 (for `u16`), but after turning it into a `Vec<u8>` it’ll be deallocated with alignment 1.

The ownership of `ptr` is effectively transferred to the `Vec<T>` which may then deallocate, reallocate or change the contents of memory pointed to by the pointer at will. Ensure that nothing else uses the pointer after calling this function.

##### Examples

    #![feature(allocator_api)]

    use std::alloc::System;

    use std::ptr;
    use std::mem;

    let mut v = Vec::with_capacity_in(3, System);
    v.push(1);
    v.push(2);
    v.push(3);

    // Prevent running `v`'s destructor so we are in complete control
    // of the allocation.
    let mut v = mem::ManuallyDrop::new(v);

    // Pull out the various important pieces of information about `v`
    let p = v.as_mut_ptr();
    let len = v.len();
    let cap = v.capacity();
    let alloc = v.allocator();

    unsafe {
        // Overwrite memory with 4, 5, 6
        for i in 0..len {
            ptr::write(p.add(i), 4 + i);
        }

        // Put everything back together into a Vec
        let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
        assert_eq!(rebuilt, [4, 5, 6]);
    }

Run

Using memory that was allocated elsewhere:

    #![feature(allocator_api)]

    use std::alloc::{AllocError, Allocator, Global, Layout};

    fn main() {
        let layout = Layout::array::<u32>(16).expect("overflow cannot happen");

        let vec = unsafe {
            let mem = match Global.allocate(layout) {
                Ok(mem) => mem.cast::<u32>().as_ptr(),
                Err(AllocError) => return,
            };

            mem.write(1_000_000);

            Vec::from_raw_parts_in(mem, 1, 16, Global)
        };

        assert_eq!(vec, &[1_000_000]);
        assert_eq!(vec.capacity(), 16);
    }

Run
source

#### pub fn into_raw_parts(self) -> (*mut T, usize, usize)

🔬This is a nightly-only experimental API. (`vec_into_raw_parts` #65816)

Decomposes a `Vec<T>` into its raw components.

Returns the raw pointer to the underlying data, the length of the vector (in elements), and the allocated capacity of the data (in elements). These are the same arguments in the same order as the arguments to `from_raw_parts`.

After calling this function, the caller is responsible for the memory previously managed by the `Vec`. The only way to do this is to convert the raw pointer, length, and capacity back into a `Vec` with the `from_raw_parts` function, allowing the destructor to perform the cleanup.

##### Examples

    #![feature(vec_into_raw_parts)]
    let v: Vec<i32> = vec![-1, 0, 1];

    let (ptr, len, cap) = v.into_raw_parts();

    let rebuilt = unsafe {
        // We can now make changes to the components, such as
        // transmuting the raw pointer to a compatible type.
        let ptr = ptr as *mut u32;

        Vec::from_raw_parts(ptr, len, cap)
    };
    assert_eq!(rebuilt, [4294967295, 0, 1]);

Run
source

#### pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A)

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Decomposes a `Vec<T>` into its raw components.

Returns the raw pointer to the underlying data, the length of the vector (in elements), the allocated capacity of the data (in elements), and the allocator. These are the same arguments in the same order as the arguments to `from_raw_parts_in`.

After calling this function, the caller is responsible for the memory previously managed by the `Vec`. The only way to do this is to convert the raw pointer, length, and capacity back into a `Vec` with the `from_raw_parts_in` function, allowing the destructor to perform the cleanup.

##### Examples

    #![feature(allocator_api, vec_into_raw_parts)]

    use std::alloc::System;

    let mut v: Vec<i32, System> = Vec::new_in(System);
    v.push(-1);
    v.push(0);
    v.push(1);

    let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();

    let rebuilt = unsafe {
        // We can now make changes to the components, such as
        // transmuting the raw pointer to a compatible type.
        let ptr = ptr as *mut u32;

        Vec::from_raw_parts_in(ptr, len, cap, alloc)
    };
    assert_eq!(rebuilt, [4294967295, 0, 1]);

Run
source

#### pub fn capacity(&self) -> usize

Returns the total number of elements the vector can hold without reallocating.

##### Examples

    let mut vec: Vec<i32> = Vec::with_capacity(10);
    vec.push(42);
    assert!(vec.capacity() >= 10);

Run
source§

### impl<T, A: Allocator> Vec<T, A, Fatal>

source

#### pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least `additional` more elements to be inserted in the given `Vec<T>`. The collection may reserve more space to speculatively avoid frequent reallocations. After calling `reserve`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if capacity is already sufficient.

##### Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

##### Examples

    let mut vec = vec![1];
    vec.reserve(10);
    assert!(vec.capacity() >= 11);

Run
source

#### pub fn reserve_exact(&mut self, additional: usize)

Reserves the minimum capacity for at least `additional` more elements to be inserted in the given `Vec<T>`. Unlike `reserve`, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling `reserve_exact`, capacity will be greater than or equal to `self.len() + additional`. Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer `reserve` if future insertions are expected.

##### Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

##### Examples

    let mut vec = vec![1];
    vec.reserve_exact(10);
    assert!(vec.capacity() >= 11);

Run
1.57.0 · source

#### pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

Tries to reserve capacity for at least `additional` more elements to be inserted in the given `Vec<T>`. The collection may reserve more space to speculatively avoid frequent reallocations. After calling `try_reserve`, capacity will be greater than or equal to `self.len() + additional` if it returns `Ok(())`. Does nothing if capacity is already sufficient. This method preserves the contents even if an error occurs.

##### Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

##### Examples

    use std::collections::TryReserveError;

    fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
        let mut output = Vec::new();

        // Pre-reserve the memory, exiting if we can't
        output.try_reserve(data.len())?;

        // Now we know this can't OOM in the middle of our complex work
        output.extend(data.iter().map(|&val| {
            val * 2 + 5 // very complicated
        }));

        Ok(output)
    }

Run
1.57.0 · source

#### pub fn try_reserve_exact( &mut self, additional: usize ) -> Result<(), TryReserveError>

Tries to reserve the minimum capacity for at least `additional` elements to be inserted in the given `Vec<T>`. Unlike `try_reserve`, this will not deliberately over-allocate to speculatively avoid frequent allocations. After calling `try_reserve_exact`, capacity will be greater than or equal to `self.len() + additional` if it returns `Ok(())`. Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer `try_reserve` if future insertions are expected.

##### Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

##### Examples

    use std::collections::TryReserveError;

    fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
        let mut output = Vec::new();

        // Pre-reserve the memory, exiting if we can't
        output.try_reserve_exact(data.len())?;

        // Now we know this can't OOM in the middle of our complex work
        output.extend(data.iter().map(|&val| {
            val * 2 + 5 // very complicated
        }));

        Ok(output)
    }

Run
source

#### pub fn shrink_to_fit(&mut self)

Shrinks the capacity of the vector as much as possible.

It will drop down as close as possible to the length but the allocator may still inform the vector that there is space for a few more elements.

##### Examples

    let mut vec = Vec::with_capacity(10);
    vec.extend([1, 2, 3]);
    assert!(vec.capacity() >= 10);
    vec.shrink_to_fit();
    assert!(vec.capacity() >= 3);

Run
1.56.0 · source

#### pub fn shrink_to(&mut self, min_capacity: usize)

Shrinks the capacity of the vector with a lower bound.

The capacity will remain at least as large as both the length and the supplied value.

If the current capacity is less than the lower limit, this is a no-op.

##### Examples

    let mut vec = Vec::with_capacity(10);
    vec.extend([1, 2, 3]);
    assert!(vec.capacity() >= 10);
    vec.shrink_to(4);
    assert!(vec.capacity() >= 4);
    vec.shrink_to(0);
    assert!(vec.capacity() >= 3);

Run
source

#### pub fn into_boxed_slice(self) -> Box<[T], A>

Converts the vector into `Box<[T]>`.

If the vector has excess capacity, its items will be moved into a newly-allocated buffer with exactly the right capacity.

##### Examples

    let v = vec![1, 2, 3];

    let slice = v.into_boxed_slice();

Run

Any excess capacity is removed:

    let mut vec = Vec::with_capacity(10);
    vec.extend([1, 2, 3]);

    assert!(vec.capacity() >= 10);
    let slice = vec.into_boxed_slice();
    assert_eq!(slice.into_vec().capacity(), 3);

Run
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### impl<T, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Identical to `try_reserve`

source

#### pub fn reserve_exact( &mut self, additional: usize ) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Identical to `try_reserve_exact`

source

#### pub fn shrink_to_fit(&mut self) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `shrink_to_fit`

source

#### pub fn shrink_to(&mut self, min_capacity: usize) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `shrink_to`

source

#### pub fn into_boxed_slice(self) -> Result<Box<[T], A>, TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `into_boxed_slice`

source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub fn truncate(&mut self, len: usize)

Shortens the vector, keeping the first `len` elements and dropping the rest.

If `len` is greater or equal to the vector’s current length, this has no effect.

The `drain` method can emulate `truncate`, but causes the excess elements to be returned instead of dropped.

Note that this method has no effect on the allocated capacity of the vector.

##### Examples

Truncating a five element vector to two elements:

    let mut vec = vec![1, 2, 3, 4, 5];
    vec.truncate(2);
    assert_eq!(vec, [1, 2]);

Run

No truncation occurs when `len` is greater than the vector’s current length:

    let mut vec = vec![1, 2, 3];
    vec.truncate(8);
    assert_eq!(vec, [1, 2, 3]);

Run

Truncating when `len == 0` is equivalent to calling the `clear` method.

    let mut vec = vec![1, 2, 3];
    vec.truncate(0);
    assert_eq!(vec, []);

Run
1.7.0 · source

#### pub fn as_slice(&self) -> &[T]

Extracts a slice containing the entire vector.

Equivalent to `&s[..]`.

##### Examples

    use std::io::{self, Write};
    let buffer = vec![1, 2, 3, 5, 8];
    io::sink().write(buffer.as_slice()).unwrap();

Run
1.7.0 · source

#### pub fn as_mut_slice(&mut self) -> &mut [T]

Extracts a mutable slice of the entire vector.

Equivalent to `&mut s[..]`.

##### Examples

    use std::io::{self, Read};
    let mut buffer = vec![0; 3];
    io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();

Run
1.37.0 · source

#### pub fn as_ptr(&self) -> *const T

Returns a raw pointer to the vector’s buffer, or a dangling raw pointer valid for zero sized reads if the vector didn’t allocate.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an `UnsafeCell`) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use `as_mut_ptr`.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying slice, and thus the returned pointer will remain valid when mixed with other calls to `as_ptr` and `as_mut_ptr`. Note that calling other methods that materialize mutable references to the slice, or mutable references to specific elements you are planning on accessing through this pointer, as well as writing to those elements, may still invalidate this pointer. See the second example below for how this guarantee can be used.

##### Examples

    let x = vec![1, 2, 4];
    let x_ptr = x.as_ptr();

    unsafe {
        for i in 0..x.len() {
            assert_eq!(*x_ptr.add(i), 1 << i);
        }
    }

Run

Due to the aliasing guarantee, the following code is legal:

    unsafe {
        let mut v = vec![0, 1, 2];
        let ptr1 = v.as_ptr();
        let _ = ptr1.read();
        let ptr2 = v.as_mut_ptr().offset(2);
        ptr2.write(2);
        // Notably, the write to `ptr2` did *not* invalidate `ptr1`
        // because it mutated a different element:
        let _ = ptr1.read();
    }

Run
1.37.0 · source

#### pub fn as_mut_ptr(&mut self) -> *mut T

Returns an unsafe mutable pointer to the vector’s buffer, or a dangling raw pointer valid for zero sized reads if the vector didn’t allocate.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying slice, and thus the returned pointer will remain valid when mixed with other calls to `as_ptr` and `as_mut_ptr`. Note that calling other methods that materialize references to the slice, or references to specific elements you are planning on accessing through this pointer, may still invalidate this pointer. See the second example below for how this guarantee can be used.

##### Examples

    // Allocate vector big enough for 4 elements.
    let size = 4;
    let mut x: Vec<i32> = Vec::with_capacity(size);
    let x_ptr = x.as_mut_ptr();

    // Initialize elements via raw pointer writes, then set length.
    unsafe {
        for i in 0..size {
            *x_ptr.add(i) = i as i32;
        }
        x.set_len(size);
    }
    assert_eq!(&*x, &[0, 1, 2, 3]);

Run

Due to the aliasing guarantee, the following code is legal:

    unsafe {
        let mut v = vec![0];
        let ptr1 = v.as_mut_ptr();
        ptr1.write(1);
        let ptr2 = v.as_mut_ptr();
        ptr2.write(2);
        // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
        ptr1.write(3);
    }

Run
source

#### pub fn allocator(&self) -> &A

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Returns a reference to the underlying allocator.

source

#### pub unsafe fn set_len(&mut self, new_len: usize)

Forces the length of the vector to `new_len`.

This is a low-level operation that maintains none of the normal invariants of the type. Normally changing the length of a vector is done using one of the safe operations instead, such as `truncate`, `resize`, `extend`, or `clear`.

##### Safety

- `new_len` must be less than or equal to `capacity()`.
- The elements at `old_len..new_len` must be initialized.

##### Examples

This method can be useful for situations in which the vector is serving as a buffer for other code, particularly over FFI:

    pub fn get_dictionary(&self) -> Option<Vec<u8>> {
        // Per the FFI method's docs, "32768 bytes is always enough".
        let mut dict = Vec::with_capacity(32_768);
        let mut dict_length = 0;
        // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
        // 1. `dict_length` elements were initialized.
        // 2. `dict_length` <= the capacity (32_768)
        // which makes `set_len` safe to call.
        unsafe {
            // Make the FFI call...
            let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
            if r == Z_OK {
                // ...and update the length to what was initialized.
                dict.set_len(dict_length);
                Some(dict)
            } else {
                None
            }
        }
    }

Run

While the following example is sound, there is a memory leak since the inner vectors were not freed prior to the `set_len` call:

    let mut vec = vec![vec![1, 0, 0],
                       vec![0, 1, 0],
                       vec![0, 0, 1]];
    // SAFETY:
    // 1. `old_len..0` is empty so no elements need to be initialized.
    // 2. `0 <= capacity` always holds whatever `capacity` is.
    unsafe {
        vec.set_len(0);
    }

Run

Normally, here, one would use `clear` instead to correctly drop the contents and thus not leak memory.

source

#### pub fn swap_remove(&mut self, index: usize) -> T

Removes an element from the vector and returns it.

The removed element is replaced by the last element of the vector.

This does not preserve ordering, but is O(1). If you need to preserve the element order, use `remove` instead.

##### Panics

Panics if `index` is out of bounds.

##### Examples

    let mut v = vec!["foo", "bar", "baz", "qux"];

    assert_eq!(v.swap_remove(1), "bar");
    assert_eq!(v, ["foo", "qux", "baz"]);

    assert_eq!(v.swap_remove(0), "foo");
    assert_eq!(v, ["baz", "qux"]);

Run
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### impl<T, A: Allocator> Vec<T, A, Fatal>

source

#### pub fn insert(&mut self, index: usize, element: T)

Inserts an element at position `index` within the vector, shifting all elements after it to the right.

##### Panics

Panics if `index > len`.

##### Examples

    let mut vec = vec![1, 2, 3];
    vec.insert(1, 4);
    assert_eq!(vec, [1, 4, 2, 3]);
    vec.insert(4, 5);
    assert_eq!(vec, [1, 4, 2, 3, 5]);

Run
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### impl<T, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn insert( &mut self, index: usize, element: T ) -> Result<(), (TryReserveError, T)>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `insert`

source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub fn remove(&mut self, index: usize) -> T

Removes and returns the element at position `index` within the vector, shifting all elements after it to the left.

Note: Because this shifts over the remaining elements, it has a worst-case performance of O(n). If you don’t need the order of elements to be preserved, use `swap_remove` instead. If you’d like to remove elements from the beginning of the `Vec`, consider using `VecDeque::pop_front` instead.

##### Panics

Panics if `index` is out of bounds.

##### Examples

    let mut v = vec![1, 2, 3];
    assert_eq!(v.remove(1), 2);
    assert_eq!(v, [1, 3]);

Run
source

#### pub fn retain<F>(&mut self, f: F)where F: FnMut(&T) -> bool,

Retains only the elements specified by the predicate.

In other words, remove all elements `e` for which `f(&e)` returns `false`. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

##### Examples

    let mut vec = vec![1, 2, 3, 4];
    vec.retain(|&x| x % 2 == 0);
    assert_eq!(vec, [2, 4]);

Run

Because the elements are visited exactly once in the original order, external state may be used to decide which elements to keep.

    let mut vec = vec![1, 2, 3, 4, 5];
    let keep = [false, true, true, false, true];
    let mut iter = keep.iter();
    vec.retain(|_| *iter.next().unwrap());
    assert_eq!(vec, [2, 3, 5]);

Run
1.61.0 · source

#### pub fn retain_mut<F>(&mut self, f: F)where F: FnMut(&mut T) -> bool,

Retains only the elements specified by the predicate, passing a mutable reference to it.

In other words, remove all elements `e` such that `f(&mut e)` returns `false`. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

##### Examples

    let mut vec = vec![1, 2, 3, 4];
    vec.retain_mut(|x| if *x <= 3 {
        *x += 1;
        true
    } else {
        false
    });
    assert_eq!(vec, [2, 3, 4]);

Run
1.16.0 · source

#### pub fn dedup_by_key<F, K>(&mut self, key: F)where F: FnMut(&mut T) -> K, K: PartialEq,

Removes all but the first of consecutive elements in the vector that resolve to the same key.

If the vector is sorted, this removes all duplicates.

##### Examples

    let mut vec = vec![10, 20, 21, 30, 20];

    vec.dedup_by_key(|i| *i / 10);

    assert_eq!(vec, [10, 20, 30, 20]);

Run
1.16.0 · source

#### pub fn dedup_by<F>(&mut self, same_bucket: F)where F: FnMut(&mut T, &mut T) -> bool,

Removes all but the first of consecutive elements in the vector satisfying a given equality relation.

The `same_bucket` function is passed references to two elements from the vector and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.

If the vector is sorted, this removes all duplicates.

##### Examples

    let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];

    vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));

    assert_eq!(vec, ["foo", "bar", "baz", "bar"]);

Run
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### impl<T, A: Allocator> Vec<T, A, Fatal>

source

#### pub fn push(&mut self, value: T)

Appends an element to the back of a collection.

##### Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

##### Examples

    let mut vec = vec![1, 2];
    vec.push(3);
    assert_eq!(vec, [1, 2, 3]);

Run
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### impl<T, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn push(&mut self, value: T) -> Result<(), (TryReserveError, T)>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `push`

source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub fn push_within_capacity(&mut self, value: T) -> Result<(), T>

🔬This is a nightly-only experimental API. (`vec_push_within_capacity` #100486)

Appends an element if there is sufficient spare capacity, otherwise an error is returned with the element.

Unlike `push` this method will not reallocate when there’s insufficient capacity. The caller should use `reserve` or `try_reserve` to ensure that there is enough capacity.

##### Examples

A manual, panic-free alternative to `FromIterator`:

    #![feature(vec_push_within_capacity)]

    use std::collections::TryReserveError;
    fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
        let mut vec = Vec::new();
        for value in iter {
            if let Err(value) = vec.push_within_capacity(value) {
                vec.try_reserve(1)?;
                // this cannot fail, the previous line either returned or added at least 1 free slot
                let _ = vec.push_within_capacity(value);
            }
        }
        Ok(vec)
    }
    assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));

Run
source

#### pub fn pop(&mut self) -> Option<T>

Removes the last element from a vector and returns it, or `None` if it is empty.

If you’d like to pop the first element, consider using `VecDeque::pop_front` instead.

##### Examples

    let mut vec = vec![1, 2, 3];
    assert_eq!(vec.pop(), Some(3));
    assert_eq!(vec, [1, 2]);

Run
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### impl<T, A: Allocator> Vec<T, A, Fatal>

1.4.0 · source

#### pub fn append(&mut self, other: &mut Self)

Moves all the elements of `other` into `self`, leaving `other` empty.

##### Panics

Panics if the new capacity exceeds `isize::MAX` bytes.

##### Examples

    let mut vec = vec![1, 2, 3];
    let mut vec2 = vec![4, 5, 6];
    vec.append(&mut vec2);
    assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
    assert_eq!(vec2, []);

Run
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### impl<T, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn append(&mut self, other: &mut Self) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `append`

source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

1.6.0 · source

#### pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A, FH> ⓘwhere R: RangeBounds<usize>,

Removes the specified range from the vector in bulk, returning all removed elements as an iterator. If the iterator is dropped before being fully consumed, it drops the remaining removed elements.

The returned iterator keeps a mutable borrow on the vector to optimize its implementation.

##### Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

##### Leaking

If the returned iterator goes out of scope without being dropped (due to `mem::forget`, for example), the vector may have lost and leaked elements arbitrarily, including elements outside the range.

##### Examples

    let mut v = vec![1, 2, 3];
    let u: Vec<_> = v.drain(1..).collect();
    assert_eq!(v, &[1]);
    assert_eq!(u, &[2, 3]);

    // A full range clears the vector, like `clear()` does
    v.drain(..);
    assert_eq!(v, &[]);

Run
source

#### pub fn clear(&mut self)

Clears the vector, removing all values.

Note that this method has no effect on the allocated capacity of the vector.

##### Examples

    let mut v = vec![1, 2, 3];

    v.clear();

    assert!(v.is_empty());

Run
source

#### pub fn len(&self) -> usize

Returns the number of elements in the vector, also referred to as its ‘length’.

##### Examples

    let a = vec![1, 2, 3];
    assert_eq!(a.len(), 3);

Run
source

#### pub fn is_empty(&self) -> bool

Returns `true` if the vector contains no elements.

##### Examples

    let mut v = Vec::new();
    assert!(v.is_empty());

    v.push(1);
    assert!(!v.is_empty());

Run
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### impl<T, A: Allocator> Vec<T, A, Fatal>

1.4.0 · source

#### pub fn split_off(&mut self, at: usize) -> Selfwhere A: Clone,

Splits the collection into two at the given index.

Returns a newly allocated vector containing the elements in the range `[at, len)`. After the call, the original vector will be left containing the elements `[0, at)` with its previous capacity unchanged.

##### Panics

Panics if `at > len`.

##### Examples

    let mut vec = vec![1, 2, 3];
    let vec2 = vec.split_off(1);
    assert_eq!(vec, [1]);
    assert_eq!(vec2, [2, 3]);

Run
1.33.0 · source

#### pub fn resize_with<F>(&mut self, new_len: usize, f: F)where F: FnMut() -> T,

Resizes the `Vec` in-place so that `len` is equal to `new_len`.

If `new_len` is greater than `len`, the `Vec` is extended by the difference, with each additional slot filled with the result of calling the closure `f`. The return values from `f` will end up in the `Vec` in the order they have been generated.

If `new_len` is less than `len`, the `Vec` is simply truncated.

This method uses a closure to create new values on every push. If you’d rather `Clone` a given value, use `Vec::resize`. If you want to use the `Default` trait to generate values, you can pass `Default::default` as the second argument.

##### Examples

    let mut vec = vec![1, 2, 3];
    vec.resize_with(5, Default::default);
    assert_eq!(vec, [1, 2, 3, 0, 0]);

    let mut vec = vec![];
    let mut p = 1;
    vec.resize_with(4, || { p *= 2; p });
    assert_eq!(vec, [2, 4, 8, 16]);

Run
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### impl<T, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn split_off(&mut self, at: usize) -> Result<Self, TryReserveError>where A: Clone,

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version fo `split_off`

source

#### pub fn resize_with<F>( &mut self, new_len: usize, f: F ) -> Result<(), TryReserveError>where F: FnMut() -> T,

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version fo `resize_with`

source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

1.47.0 · source

#### pub fn leak<'a>(self) -> &'a mut [T]where A: 'a,

Consumes and leaks the `Vec`, returning a mutable reference to the contents, `&'a mut [T]`. Note that the type `T` must outlive the chosen lifetime `'a`. If the type has only static references, or none at all, then this may be chosen to be `'static`.

As of Rust 1.57, this method does not reallocate or shrink the `Vec`, so the leaked allocation may include unused capacity that is not part of the returned slice.

This function is mainly useful for data that lives for the remainder of the program’s life. Dropping the returned reference will cause a memory leak.

##### Examples

Simple usage:

    let x = vec![1, 2, 3];
    let static_ref: &'static mut [usize] = x.leak();
    static_ref[0] += 1;
    assert_eq!(static_ref, &[2, 2, 3]);

Run
1.60.0 · source

#### pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>]

Returns the remaining spare capacity of the vector as a slice of `MaybeUninit<T>`.

The returned slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the `set_len` method.

##### Examples

    // Allocate vector big enough for 10 elements.
    let mut v = Vec::with_capacity(10);

    // Fill in the first 3 elements.
    let uninit = v.spare_capacity_mut();
    uninit[0].write(0);
    uninit[1].write(1);
    uninit[2].write(2);

    // Mark the first 3 elements of the vector as being initialized.
    unsafe {
        v.set_len(3);
    }

    assert_eq!(&v, &[0, 1, 2]);

Run
source

#### pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>])

🔬This is a nightly-only experimental API. (`vec_split_at_spare` #81944)

Returns vector content as a slice of `T`, along with the remaining spare capacity of the vector as a slice of `MaybeUninit<T>`.

The returned spare capacity slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the `set_len` method.

Note that this is a low-level API, which should be used with care for optimization purposes. If you need to append data to a `Vec` you can use `push`, `extend`, `extend_from_slice`, `extend_from_within`, `insert`, `append`, `resize` or `resize_with`, depending on your exact needs.

##### Examples

    #![feature(vec_split_at_spare)]

    let mut v = vec![1, 1, 2];

    // Reserve additional space big enough for 10 elements.
    v.reserve(10);

    let (init, uninit) = v.split_at_spare_mut();
    let sum = init.iter().copied().sum::<u32>();

    // Fill in the next 4 elements.
    uninit[0].write(sum);
    uninit[1].write(sum * 2);
    uninit[2].write(sum * 3);
    uninit[3].write(sum * 4);

    // Mark the 4 elements of the vector as being initialized.
    unsafe {
        let len = v.len();
        v.set_len(len + 4);
    }

    assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);

Run
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### impl<T: Clone, A: Allocator> Vec<T, A, Fatal>

1.5.0 · source

#### pub fn resize(&mut self, new_len: usize, value: T)

Resizes the `Vec` in-place so that `len` is equal to `new_len`.

If `new_len` is greater than `len`, the `Vec` is extended by the difference, with each additional slot filled with `value`. If `new_len` is less than `len`, the `Vec` is simply truncated.

This method requires `T` to implement `Clone`, in order to be able to clone the passed value. If you need more flexibility (or want to rely on `Default` instead of `Clone`), use `Vec::resize_with`. If you only need to resize to a smaller size, use `Vec::truncate`.

##### Examples

    let mut vec = vec!["hello"];
    vec.resize(3, "world");
    assert_eq!(vec, ["hello", "world", "world"]);

    let mut vec = vec![1, 2, 3, 4];
    vec.resize(2, 0);
    assert_eq!(vec, [1, 2]);

Run
1.6.0 · source

#### pub fn extend_from_slice(&mut self, other: &[T])

Clones and appends all elements in a slice to the `Vec`.

Iterates over the slice `other`, clones each element, and then appends it to this `Vec`. The `other` slice is traversed in-order.

Note that this function is same as `extend` except that it is specialized to work with slices instead. If and when Rust gets specialization this function will likely be deprecated (but still available).

##### Examples

    let mut vec = vec![1];
    vec.extend_from_slice(&[2, 3, 4]);
    assert_eq!(vec, [1, 2, 3, 4]);

Run
1.53.0 · source

#### pub fn extend_from_within<R>(&mut self, src: R)where R: RangeBounds<usize>,

Copies elements from `src` range to the end of the vector.

##### Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

##### Examples

    let mut vec = vec![0, 1, 2, 3, 4];

    vec.extend_from_within(2..);
    assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);

    vec.extend_from_within(..2);
    assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);

    vec.extend_from_within(4..8);
    assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);

Run
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### impl<T: Clone, A: Allocator> Vec<T, A, Fallible>

source

#### pub fn resize( &mut self, new_len: usize, value: T ) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `resize`

source

#### pub fn extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError>

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `extend_from_slice`

source

#### pub fn extend_from_within<R>(&mut self, src: R) -> Result<(), TryReserveError>where R: RangeBounds<usize>,

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Fallible version of `extend_from_within`

source§

### impl<T, A: Allocator, FH: FailureHandling, const N: usize> Vec<[T; N], A, FH>

source

#### pub fn into_flattened(self) -> Vec<T, A>

🔬This is a nightly-only experimental API. (`slice_flatten` #95629)

Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.

##### Panics

Panics if the length of the resulting vector would overflow a `usize`.

This is only possible when flattening a vector of arrays of zero-sized types, and thus tends to be irrelevant in practice. If `size_of::<T>() > 0`, this will never panic.

##### Examples

    #![feature(slice_flatten)]

    let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
    assert_eq!(vec.pop(), Some([7, 8, 9]));

    let mut flattened = vec.into_flattened();
    assert_eq!(flattened.pop(), Some(6));

Run
source§

### impl<T: PartialEq, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub fn dedup(&mut self)

Removes consecutive repeated elements in the vector according to the `PartialEq` trait implementation.

If the vector is sorted, this removes all duplicates.

##### Examples

    let mut vec = vec![1, 2, 2, 3, 2];

    vec.dedup();

    assert_eq!(vec, [1, 2, 3, 2]);

Run
source§

### impl<T, A: Allocator> Vec<T, A, Fatal>

1.21.0 · source

#### pub fn splice<R, I>( &mut self, range: R, replace_with: I ) -> Splice<'_, I::IntoIter, A> ⓘwhere R: RangeBounds<usize>, I: IntoIterator<Item = T>,

Creates a splicing iterator that replaces the specified range in the vector with the given `replace_with` iterator and yields the removed items. `replace_with` does not need to be the same length as `range`.

`range` is removed even if the iterator is not consumed until the end.

It is unspecified how many elements are removed from the vector if the `Splice` value is leaked.

The input iterator `replace_with` is only consumed when the `Splice` value is dropped.

This is optimal if:

- The tail (elements in the vector after `range`) is empty,
- or `replace_with` yields fewer or equal elements than `range`’s length
- or the lower bound of its `size_hint()` is exact.

Otherwise, a temporary vector is allocated and the tail is moved twice.

##### Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

##### Examples

    let mut v = vec![1, 2, 3, 4];
    let new = [7, 8, 9];
    let u: Vec<_> = v.splice(1..3, new).collect();
    assert_eq!(v, &[1, 7, 8, 9, 4]);
    assert_eq!(u, &[2, 3]);

Run
source§

### impl<T, A: Allocator, FH: FailureHandling> Vec<T, A, FH>

source

#### pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A, FH> ⓘwhere F: FnMut(&mut T) -> bool,

🔬This is a nightly-only experimental API. (`extract_if` #43244)

Creates an iterator which uses a closure to determine if an element should be removed.

If the closure returns true, then the element is removed and yielded. If the closure returns false, the element will remain in the vector and will not be yielded by the iterator.

If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating or the iteration short-circuits, then the remaining elements will be retained. Use `retain` with a negated predicate if you do not need the returned iterator.

Using this method is equivalent to the following code:

    let mut i = 0;
    while i < vec.len() {
        if some_predicate(&mut vec[i]) {
            let val = vec.remove(i);
            // your code here
        } else {
            i += 1;
        }
    }

Run

But `extract_if` is easier to use. `extract_if` is also more efficient, because it can backshift the elements of the array in bulk.

Note that `extract_if` also lets you mutate every element in the filter closure, regardless of whether you choose to keep or remove it.

##### Examples

Splitting an array into evens and odds, reusing the original allocation:

    #![feature(extract_if)]
    let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];

    let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
    let odds = numbers;

    assert_eq!(evens, vec![2, 4, 6, 8, 14]);
    assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);

Run

## Methods from Deref<Target = [T]>§

source

#### pub fn sort(&mut self)where T: Ord,

Sorts the slice.

This sort is stable (i.e., does not reorder equal elements) and O(n * log(n)) worst-case.

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See `sort_unstable`.

##### Current implementation

The current algorithm is an adaptive, iterative merge sort inspired by timsort. It is designed to be very fast in cases where the slice is nearly sorted, or consists of two or more sorted sequences concatenated one after another.

Also, it allocates temporary storage half the size of `self`, but for short slices a non-allocating insertion sort is used instead.

##### Examples

    let mut v = [-5, 4, 1, -3, 2];

    v.sort();
    assert!(v == [-5, -3, 1, 2, 4]);

Run
source

#### pub fn sort_by<F>(&mut self, compare: F)where F: FnMut(&T, &T) -> Ordering,

Sorts the slice with a comparator function.

This sort is stable (i.e., does not reorder equal elements) and O(n * log(n)) worst-case.

The comparator function must define a total ordering for the elements in the slice. If the ordering is not total, the order of the elements is unspecified. An order is a total order if it is (for all `a`, `b` and `c`):

- total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
- transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.

For example, while `f64` doesn’t implement `Ord` because `NaN != NaN`, we can use `partial_cmp` as our sort function when we know the slice doesn’t contain a `NaN`.

    let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
    floats.sort_by(|a, b| a.partial_cmp(b).unwrap());
    assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);

Run

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See `sort_unstable_by`.

##### Current implementation

The current algorithm is an adaptive, iterative merge sort inspired by timsort. It is designed to be very fast in cases where the slice is nearly sorted, or consists of two or more sorted sequences concatenated one after another.

Also, it allocates temporary storage half the size of `self`, but for short slices a non-allocating insertion sort is used instead.

##### Examples

    let mut v = [5, 4, 1, 3, 2];
    v.sort_by(|a, b| a.cmp(b));
    assert!(v == [1, 2, 3, 4, 5]);

    // reverse sorting
    v.sort_by(|a, b| b.cmp(a));
    assert!(v == [5, 4, 3, 2, 1]);

Run
1.7.0 · source

#### pub fn sort_by_key<K, F>(&mut self, f: F)where F: FnMut(&T) -> K, K: Ord,

Sorts the slice with a key extraction function.

This sort is stable (i.e., does not reorder equal elements) and O(m * n * log(n)) worst-case, where the key function is O(m).

For expensive key functions (e.g. functions that are not simple property accesses or basic operations), `sort_by_cached_key` is likely to be significantly faster, as it does not recompute element keys.

When applicable, unstable sorting is preferred because it is generally faster than stable sorting and it doesn’t allocate auxiliary memory. See `sort_unstable_by_key`.

##### Current implementation

The current algorithm is an adaptive, iterative merge sort inspired by timsort. It is designed to be very fast in cases where the slice is nearly sorted, or consists of two or more sorted sequences concatenated one after another.

Also, it allocates temporary storage half the size of `self`, but for short slices a non-allocating insertion sort is used instead.

##### Examples

    let mut v = [-5i32, 4, 1, -3, 2];

    v.sort_by_key(|k| k.abs());
    assert!(v == [1, 2, -3, 4, -5]);

Run
1.34.0 · source

#### pub fn sort_by_cached_key<K, F>(&mut self, f: F)where F: FnMut(&T) -> K, K: Ord,

Sorts the slice with a key extraction function.

During sorting, the key function is called at most once per element, by using temporary storage to remember the results of key evaluation. The order of calls to the key function is unspecified and may change in future versions of the standard library.

This sort is stable (i.e., does not reorder equal elements) and O(m * n + n * log(n)) worst-case, where the key function is O(m).

For simple key functions (e.g., functions that are property accesses or basic operations), `sort_by_key` is likely to be faster.

##### Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the length of the slice.

##### Examples

    let mut v = [-5i32, 4, 32, -3, 2];

    v.sort_by_cached_key(|k| k.to_string());
    assert!(v == [-3, -5, 2, 32, 4]);

Run
source

#### pub fn to_vec(&self) -> Vec<T>where T: Clone,

Copies `self` into a new `Vec`.

##### Examples

    let s = [10, 40, 30];
    let x = s.to_vec();
    // Here, `s` and `x` can be modified independently.

Run
source

#### pub fn to_vec_in<A: Allocator>(&self, alloc: A) -> Vec<T, A>where T: Clone,

🔬This is a nightly-only experimental API. (`allocator_api` #32838)

Copies `self` into a new `Vec` with an allocator.

##### Examples

    #![feature(allocator_api)]

    use std::alloc::System;

    let s = [10, 40, 30];
    let x = s.to_vec_in(System);
    // Here, `s` and `x` can be modified independently.

Run
1.40.0 · source

#### pub fn repeat(&self, n: usize) -> Vec<T>where T: Copy,

Creates a vector by copying a slice `n` times.

##### Panics

This function will panic if the capacity would overflow.

##### Examples

Basic usage:

    assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]);

Run

A panic upon overflow:

ⓘ

    // this will panic at runtime
    b"0123456789abcdef".repeat(usize::MAX);

Run
source

#### pub fn concat<Item: ?Sized>(&self) -> <Self as Concat<Item>>::Output where Self: Concat<Item>,

Flattens a slice of `T` into a single value `Self::Output`.

##### Examples

    assert_eq!(["hello", "world"].concat(), "helloworld");
    assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);

Run
1.3.0 · source

#### pub fn join<Separator>( &self, sep: Separator ) -> <Self as Join<Separator>>::Output where Self: Join<Separator>,

Flattens a slice of `T` into a single value `Self::Output`, placing a given separator between each.

##### Examples

    assert_eq!(["hello", "world"].join(" "), "hello world");
    assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
    assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]);

Run
source

#### pub fn connect<Separator>( &self, sep: Separator ) -> <Self as Join<Separator>>::Output where Self: Join<Separator>,

👎Deprecated since 1.3.0: renamed to join

Flattens a slice of `T` into a single value `Self::Output`, placing a given separator between each.

##### Examples

    assert_eq!(["hello", "world"].connect(" "), "hello world");
    assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]);

Run
1.23.0 · source

#### pub fn to_ascii_uppercase(&self) -> Vec<u8>

Returns a vector containing a copy of this slice where each byte is mapped to its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use `make_ascii_uppercase`.

1.23.0 · source

#### pub fn to_ascii_lowercase(&self) -> Vec<u8>

Returns a vector containing a copy of this slice where each byte is mapped to its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use `make_ascii_lowercase`.

1.23.0 · source

#### pub fn is_ascii(&self) -> bool

Checks if all bytes in this slice are within the ASCII range.

source

#### pub fn as_ascii(&self) -> Option<&[AsciiChar]>

🔬This is a nightly-only experimental API. (`ascii_char` #110998)

If this slice `is_ascii`, returns it as a slice of ASCII characters, otherwise returns `None`.

source

#### pub unsafe fn as_ascii_unchecked(&self) -> &[AsciiChar]

🔬This is a nightly-only experimental API. (`ascii_char` #110998)

Converts this slice of bytes into a slice of ASCII characters, without checking whether they’re valid.

##### Safety

Every byte in the slice must be in `0..=127`, or else this is UB.

1.23.0 · source

#### pub fn eq_ignore_ascii_case(&self, other: &[u8]) -> bool

Checks that two slices are an ASCII case-insensitive match.

Same as `to_ascii_lowercase(a) == to_ascii_lowercase(b)`, but without allocating and copying temporaries.

1.23.0 · source

#### pub fn make_ascii_uppercase(&mut self)

Converts this slice to its ASCII upper case equivalent in-place.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To return a new uppercased value without modifying the existing one, use `to_ascii_uppercase`.

1.23.0 · source

#### pub fn make_ascii_lowercase(&mut self)

Converts this slice to its ASCII lower case equivalent in-place.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To return a new lowercased value without modifying the existing one, use `to_ascii_lowercase`.

1.60.0 · source

#### pub fn escape_ascii(&self) -> EscapeAscii<'_> ⓘ

Returns an iterator that produces an escaped version of this slice, treating it as an ASCII string.

##### Examples

    let s = b"0\t\r\n'\"\\\x9d";
    let escaped = s.escape_ascii().to_string();
    assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");

Run
source

#### pub fn trim_ascii_start(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`byte_slice_trim_ascii` #94035)

Returns a byte slice with leading ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### Examples

    #![feature(byte_slice_trim_ascii)]

    assert_eq!(b" \t hello world\n".trim_ascii_start(), b"hello world\n");
    assert_eq!(b"  ".trim_ascii_start(), b"");
    assert_eq!(b"".trim_ascii_start(), b"");

Run
source

#### pub fn trim_ascii_end(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`byte_slice_trim_ascii` #94035)

Returns a byte slice with trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### Examples

    #![feature(byte_slice_trim_ascii)]

    assert_eq!(b"\r hello world\n ".trim_ascii_end(), b"\r hello world");
    assert_eq!(b"  ".trim_ascii_end(), b"");
    assert_eq!(b"".trim_ascii_end(), b"");

Run
source

#### pub fn trim_ascii(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`byte_slice_trim_ascii` #94035)

Returns a byte slice with leading and trailing ASCII whitespace bytes removed.

‘Whitespace’ refers to the definition used by `u8::is_ascii_whitespace`.

##### Examples

    #![feature(byte_slice_trim_ascii)]

    assert_eq!(b"\r hello world\n ".trim_ascii(), b"hello world");
    assert_eq!(b"  ".trim_ascii(), b"");
    assert_eq!(b"".trim_ascii(), b"");

Run
source

#### pub fn sort_floats(&mut self)

🔬This is a nightly-only experimental API. (`sort_floats` #93396)

Sorts the slice of floats.

This sort is in-place (i.e. does not allocate), O(n * log(n)) worst-case, and uses the ordering defined by `f64::total_cmp`.

##### Current implementation

This uses the same sorting algorithm as `sort_unstable_by`.

##### Examples

    #![feature(sort_floats)]
    let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];

    v.sort_floats();
    let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
    assert_eq!(&v[..8], &sorted[..8]);
    assert!(v[8].is_nan());

Run
source

#### pub fn flatten(&self) -> &[T]

🔬This is a nightly-only experimental API. (`slice_flatten` #95629)

Takes a `&[[T; N]]`, and flattens it to a `&[T]`.

##### Panics

This panics if the length of the resulting slice would overflow a `usize`.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If `size_of::<T>() > 0`, this will never panic.

##### Examples

    #![feature(slice_flatten)]

    assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);

    assert_eq!(
        [[1, 2, 3], [4, 5, 6]].flatten(),
        [[1, 2], [3, 4], [5, 6]].flatten(),
    );

    let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
    assert!(slice_of_empty_arrays.flatten().is_empty());

    let empty_slice_of_arrays: &[[u32; 10]] = &[];
    assert!(empty_slice_of_arrays.flatten().is_empty());

Run
source

#### pub fn flatten_mut(&mut self) -> &mut [T]

🔬This is a nightly-only experimental API. (`slice_flatten` #95629)

Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.

##### Panics

This panics if the length of the resulting slice would overflow a `usize`.

This is only possible when flattening a slice of arrays of zero-sized types, and thus tends to be irrelevant in practice. If `size_of::<T>() > 0`, this will never panic.

##### Examples

    #![feature(slice_flatten)]

    fn add_5_to_all(slice: &mut [i32]) {
        for i in slice {
            *i += 5;
        }
    }

    let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
    add_5_to_all(array.flatten_mut());
    assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);

Run
source

#### pub fn len(&self) -> usize

Returns the number of elements in the slice.

##### Examples

    let a = [1, 2, 3];
    assert_eq!(a.len(), 3);

Run
source

#### pub fn is_empty(&self) -> bool

Returns `true` if the slice has a length of 0.

##### Examples

    let a = [1, 2, 3];
    assert!(!a.is_empty());

Run
source

#### pub fn first(&self) -> Option<&T>

Returns the first element of the slice, or `None` if it is empty.

##### Examples

    let v = [10, 40, 30];
    assert_eq!(Some(&10), v.first());

    let w: &[i32] = &[];
    assert_eq!(None, w.first());

Run
source

#### pub fn first_mut(&mut self) -> Option<&mut T>

Returns a mutable pointer to the first element of the slice, or `None` if it is empty.

##### Examples

    let x = &mut [0, 1, 2];

    if let Some(first) = x.first_mut() {
        *first = 5;
    }
    assert_eq!(x, &[5, 1, 2]);

Run
1.5.0 · source

#### pub fn split_first(&self) -> Option<(&T, &[T])>

Returns the first and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    let x = &[0, 1, 2];

    if let Some((first, elements)) = x.split_first() {
        assert_eq!(first, &0);
        assert_eq!(elements, &[1, 2]);
    }

Run
1.5.0 · source

#### pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])>

Returns the first and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    let x = &mut [0, 1, 2];

    if let Some((first, elements)) = x.split_first_mut() {
        *first = 3;
        elements[0] = 4;
        elements[1] = 5;
    }
    assert_eq!(x, &[3, 4, 5]);

Run
1.5.0 · source

#### pub fn split_last(&self) -> Option<(&T, &[T])>

Returns the last and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    let x = &[0, 1, 2];

    if let Some((last, elements)) = x.split_last() {
        assert_eq!(last, &2);
        assert_eq!(elements, &[0, 1]);
    }

Run
1.5.0 · source

#### pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])>

Returns the last and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    let x = &mut [0, 1, 2];

    if let Some((last, elements)) = x.split_last_mut() {
        *last = 3;
        elements[0] = 4;
        elements[1] = 5;
    }
    assert_eq!(x, &[4, 5, 3]);

Run
source

#### pub fn last(&self) -> Option<&T>

Returns the last element of the slice, or `None` if it is empty.

##### Examples

    let v = [10, 40, 30];
    assert_eq!(Some(&30), v.last());

    let w: &[i32] = &[];
    assert_eq!(None, w.last());

Run
source

#### pub fn last_mut(&mut self) -> Option<&mut T>

Returns a mutable pointer to the last item in the slice.

##### Examples

    let x = &mut [0, 1, 2];

    if let Some(last) = x.last_mut() {
        *last = 10;
    }
    assert_eq!(x, &[0, 1, 10]);

Run
source

#### pub fn first_chunk<const N: usize>(&self) -> Option<&[T; N]>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns the first `N` elements of the slice, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let u = [10, 40, 30];
    assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());

    let v: &[i32] = &[10];
    assert_eq!(None, v.first_chunk::<2>());

    let w: &[i32] = &[];
    assert_eq!(Some(&[]), w.first_chunk::<0>());

Run
source

#### pub fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns a mutable reference to the first `N` elements of the slice, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &mut [0, 1, 2];

    if let Some(first) = x.first_chunk_mut::<2>() {
        first[0] = 5;
        first[1] = 4;
    }
    assert_eq!(x, &[5, 4, 2]);

Run
source

#### pub fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns the first `N` elements of the slice and the remainder, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &[0, 1, 2];

    if let Some((first, elements)) = x.split_first_chunk::<2>() {
        assert_eq!(first, &[0, 1]);
        assert_eq!(elements, &[2]);
    }

Run
source

#### pub fn split_first_chunk_mut<const N: usize>( &mut self ) -> Option<(&mut [T; N], &mut [T])>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns a mutable reference to the first `N` elements of the slice and the remainder, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &mut [0, 1, 2];

    if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
        first[0] = 3;
        first[1] = 4;
        elements[0] = 5;
    }
    assert_eq!(x, &[3, 4, 5]);

Run
source

#### pub fn split_last_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns the last `N` elements of the slice and the remainder, or `None` if it has fewer than `N` elements.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &[0, 1, 2];

    if let Some((last, elements)) = x.split_last_chunk::<2>() {
        assert_eq!(last, &[1, 2]);
        assert_eq!(elements, &[0]);
    }

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#### pub fn split_last_chunk_mut<const N: usize>( &mut self ) -> Option<(&mut [T; N], &mut [T])>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns the last and all the rest of the elements of the slice, or `None` if it is empty.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &mut [0, 1, 2];

    if let Some((last, elements)) = x.split_last_chunk_mut::<2>() {
        last[0] = 3;
        last[1] = 4;
        elements[0] = 5;
    }
    assert_eq!(x, &[5, 3, 4]);

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#### pub fn last_chunk<const N: usize>(&self) -> Option<&[T; N]>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns the last element of the slice, or `None` if it is empty.

##### Examples

    #![feature(slice_first_last_chunk)]

    let u = [10, 40, 30];
    assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());

    let v: &[i32] = &[10];
    assert_eq!(None, v.last_chunk::<2>());

    let w: &[i32] = &[];
    assert_eq!(Some(&[]), w.last_chunk::<0>());

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#### pub fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>

🔬This is a nightly-only experimental API. (`slice_first_last_chunk` #111774)

Returns a mutable pointer to the last item in the slice.

##### Examples

    #![feature(slice_first_last_chunk)]

    let x = &mut [0, 1, 2];

    if let Some(last) = x.last_chunk_mut::<2>() {
        last[0] = 10;
        last[1] = 20;
    }
    assert_eq!(x, &[0, 10, 20]);

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#### pub fn get<I>(&self, index: I) -> Option<&<I as SliceIndex<[T]>>::Output>where I: SliceIndex<[T]>,

Returns a reference to an element or subslice depending on the type of index.

- If given a position, returns a reference to the element at that position or `None` if out of bounds.
- If given a range, returns the subslice corresponding to that range, or `None` if out of bounds.

##### Examples

    let v = [10, 40, 30];
    assert_eq!(Some(&40), v.get(1));
    assert_eq!(Some(&[10, 40][..]), v.get(0..2));
    assert_eq!(None, v.get(3));
    assert_eq!(None, v.get(0..4));

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#### pub fn get_mut<I>( &mut self, index: I ) -> Option<&mut <I as SliceIndex<[T]>>::Output>where I: SliceIndex<[T]>,

Returns a mutable reference to an element or subslice depending on the type of index (see `get`) or `None` if the index is out of bounds.

##### Examples

    let x = &mut [0, 1, 2];

    if let Some(elem) = x.get_mut(1) {
        *elem = 42;
    }
    assert_eq!(x, &[0, 42, 2]);

Run
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#### pub unsafe fn get_unchecked<I>( &self, index: I ) -> &<I as SliceIndex<[T]>>::Output where I: SliceIndex<[T]>,

Returns a reference to an element or subslice, without doing bounds checking.

For a safe alternative see `get`.

##### Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

##### Examples

    let x = &[1, 2, 4];

    unsafe {
        assert_eq!(x.get_unchecked(1), &2);
    }

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#### pub unsafe fn get_unchecked_mut<I>( &mut self, index: I ) -> &mut <I as SliceIndex<[T]>>::Output where I: SliceIndex<[T]>,

Returns a mutable reference to an element or subslice, without doing bounds checking.

For a safe alternative see `get_mut`.

##### Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used.

##### Examples

    let x = &mut [1, 2, 4];

    unsafe {
        let elem = x.get_unchecked_mut(1);
        *elem = 13;
    }
    assert_eq!(x, &[1, 13, 4]);

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#### pub fn as_ptr(&self) -> *const T

Returns a raw pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an `UnsafeCell`) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use `as_mut_ptr`.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

##### Examples

    let x = &[1, 2, 4];
    let x_ptr = x.as_ptr();

    unsafe {
        for i in 0..x.len() {
            assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
        }
    }

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#### pub fn as_mut_ptr(&mut self) -> *mut T

Returns an unsafe mutable pointer to the slice’s buffer.

The caller must ensure that the slice outlives the pointer this function returns, or else it will end up pointing to garbage.

Modifying the container referenced by this slice may cause its buffer to be reallocated, which would also make any pointers to it invalid.

##### Examples

    let x = &mut [1, 2, 4];
    let x_ptr = x.as_mut_ptr();

    unsafe {
        for i in 0..x.len() {
            *x_ptr.add(i) += 2;
        }
    }
    assert_eq!(x, &[3, 4, 6]);

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1.48.0 · source

#### pub fn as_ptr_range(&self) -> Range<*const T>

Returns the two raw pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See `as_ptr` for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

It can also be useful to check if a pointer to an element refers to an element of this slice:

    let a = [1, 2, 3];
    let x = &a[1] as *const _;
    let y = &5 as *const _;

    assert!(a.as_ptr_range().contains(&x));
    assert!(!a.as_ptr_range().contains(&y));

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1.48.0 · source

#### pub fn as_mut_ptr_range(&mut self) -> Range<*mut T>

Returns the two unsafe mutable pointers spanning the slice.

The returned range is half-open, which means that the end pointer points one past the last element of the slice. This way, an empty slice is represented by two equal pointers, and the difference between the two pointers represents the size of the slice.

See `as_mut_ptr` for warnings on using these pointers. The end pointer requires extra caution, as it does not point to a valid element in the slice.

This function is useful for interacting with foreign interfaces which use two pointers to refer to a range of elements in memory, as is common in C++.

source

#### pub fn swap(&mut self, a: usize, b: usize)

Swaps two elements in the slice.

If `a` equals to `b`, it’s guaranteed that elements won’t change value.

##### Arguments

- a - The index of the first element
- b - The index of the second element

##### Panics

Panics if `a` or `b` are out of bounds.

##### Examples

    let mut v = ["a", "b", "c", "d", "e"];
    v.swap(2, 4);
    assert!(v == ["a", "b", "e", "d", "c"]);

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#### pub unsafe fn swap_unchecked(&mut self, a: usize, b: usize)

🔬This is a nightly-only experimental API. (`slice_swap_unchecked` #88539)

Swaps two elements in the slice, without doing bounds checking.

For a safe alternative see `swap`.

##### Arguments

- a - The index of the first element
- b - The index of the second element

##### Safety

Calling this method with an out-of-bounds index is undefined behavior. The caller has to ensure that `a < self.len()` and `b < self.len()`.

##### Examples

    #![feature(slice_swap_unchecked)]

    let mut v = ["a", "b", "c", "d"];
    // SAFETY: we know that 1 and 3 are both indices of the slice
    unsafe { v.swap_unchecked(1, 3) };
    assert!(v == ["a", "d", "c", "b"]);

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#### pub fn reverse(&mut self)

Reverses the order of elements in the slice, in place.

##### Examples

    let mut v = [1, 2, 3];
    v.reverse();
    assert!(v == [3, 2, 1]);

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#### pub fn iter(&self) -> Iter<'_, T> ⓘ

Returns an iterator over the slice.

The iterator yields all items from start to end.

##### Examples

    let x = &[1, 2, 4];
    let mut iterator = x.iter();

    assert_eq!(iterator.next(), Some(&1));
    assert_eq!(iterator.next(), Some(&2));
    assert_eq!(iterator.next(), Some(&4));
    assert_eq!(iterator.next(), None);

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#### pub fn iter_mut(&mut self) -> IterMut<'_, T> ⓘ

Returns an iterator that allows modifying each value.

The iterator yields all items from start to end.

##### Examples

    let x = &mut [1, 2, 4];
    for elem in x.iter_mut() {
        *elem += 2;
    }
    assert_eq!(x, &[3, 4, 6]);

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#### pub fn windows(&self, size: usize) -> Windows<'_, T> ⓘ

Returns an iterator over all contiguous windows of length `size`. The windows overlap. If the slice is shorter than `size`, the iterator returns no values.

##### Panics

Panics if `size` is 0.

##### Examples

    let slice = ['r', 'u', 's', 't'];
    let mut iter = slice.windows(2);
    assert_eq!(iter.next().unwrap(), &['r', 'u']);
    assert_eq!(iter.next().unwrap(), &['u', 's']);
    assert_eq!(iter.next().unwrap(), &['s', 't']);
    assert!(iter.next().is_none());

Run

If the slice is shorter than `size`:

    let slice = ['f', 'o', 'o'];
    let mut iter = slice.windows(4);
    assert!(iter.next().is_none());

Run

There’s no `windows_mut`, as that existing would let safe code violate the “only one `&mut` at a time to the same thing” rule. However, you can sometimes use `Cell::as_slice_of_cells` in conjunction with `windows` to accomplish something similar:

    use std::cell::Cell;

    let mut array = ['R', 'u', 's', 't', ' ', '2', '0', '1', '5'];
    let slice = &mut array[..];
    let slice_of_cells: &[Cell<char>] = Cell::from_mut(slice).as_slice_of_cells();
    for w in slice_of_cells.windows(3) {
        Cell::swap(&w[0], &w[2]);
    }
    assert_eq!(array, ['s', 't', ' ', '2', '0', '1', '5', 'u', 'R']);

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#### pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last chunk will not have length `chunk_size`.

See `chunks_exact` for a variant of this iterator that returns chunks of always exactly `chunk_size` elements, and `rchunks` for the same iterator but starting at the end of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.chunks(2);
    assert_eq!(iter.next().unwrap(), &['l', 'o']);
    assert_eq!(iter.next().unwrap(), &['r', 'e']);
    assert_eq!(iter.next().unwrap(), &['m']);
    assert!(iter.next().is_none());

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#### pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the length of the slice, then the last chunk will not have length `chunk_size`.

See `chunks_exact_mut` for a variant of this iterator that returns chunks of always exactly `chunk_size` elements, and `rchunks_mut` for the same iterator but starting at the end of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    for chunk in v.chunks_mut(2) {
        for elem in chunk.iter_mut() {
            *elem += count;
        }
        count += 1;
    }
    assert_eq!(v, &[1, 1, 2, 2, 3]);

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1.31.0 · source

#### pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the beginning of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved from the `remainder` function of the iterator.

Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the resulting code better than in the case of `chunks`.

See `chunks` for a variant of this iterator that also returns the remainder as a smaller chunk, and `rchunks_exact` for the same iterator but starting at the end of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.chunks_exact(2);
    assert_eq!(iter.next().unwrap(), &['l', 'o']);
    assert_eq!(iter.next().unwrap(), &['r', 'e']);
    assert!(iter.next().is_none());
    assert_eq!(iter.remainder(), &['m']);

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1.31.0 · source

#### pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved from the `into_remainder` function of the iterator.

Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the resulting code better than in the case of `chunks_mut`.

See `chunks_mut` for a variant of this iterator that also returns the remainder as a smaller chunk, and `rchunks_exact_mut` for the same iterator but starting at the end of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    for chunk in v.chunks_exact_mut(2) {
        for elem in chunk.iter_mut() {
            *elem += count;
        }
        count += 1;
    }
    assert_eq!(v, &[1, 1, 2, 2, 0]);

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#### pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]]

🔬This is a nightly-only experimental API. (`slice_as_chunks` #74985)

Splits the slice into a slice of `N`-element arrays, assuming that there’s no remainder.

##### Safety

This may only be called when

- The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
- `N != 0`.

##### Examples

    #![feature(slice_as_chunks)]
    let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
    let chunks: &[[char; 1]] =
        // SAFETY: 1-element chunks never have remainder
        unsafe { slice.as_chunks_unchecked() };
    assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
    let chunks: &[[char; 3]] =
        // SAFETY: The slice length (6) is a multiple of 3
        unsafe { slice.as_chunks_unchecked() };
    assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);

    // These would be unsound:
    // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
    // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed

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#### pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T])

🔬This is a nightly-only experimental API. (`slice_as_chunks` #74985)

Splits the slice into a slice of `N`-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than `N`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(slice_as_chunks)]
    let slice = ['l', 'o', 'r', 'e', 'm'];
    let (chunks, remainder) = slice.as_chunks();
    assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
    assert_eq!(remainder, &['m']);

Run

If you expect the slice to be an exact multiple, you can combine `let`-`else` with an empty slice pattern:

    #![feature(slice_as_chunks)]
    let slice = ['R', 'u', 's', 't'];
    let (chunks, []) = slice.as_chunks::<2>() else {
        panic!("slice didn't have even length")
    };
    assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);

Run
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#### pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]])

🔬This is a nightly-only experimental API. (`slice_as_chunks` #74985)

Splits the slice into a slice of `N`-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than `N`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(slice_as_chunks)]
    let slice = ['l', 'o', 'r', 'e', 'm'];
    let (remainder, chunks) = slice.as_rchunks();
    assert_eq!(remainder, &['l']);
    assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);

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#### pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> ⓘ

🔬This is a nightly-only experimental API. (`array_chunks` #74985)

Returns an iterator over `N` elements of the slice at a time, starting at the beginning of the slice.

The chunks are array references and do not overlap. If `N` does not divide the length of the slice, then the last up to `N-1` elements will be omitted and can be retrieved from the `remainder` function of the iterator.

This method is the const generic equivalent of `chunks_exact`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(array_chunks)]
    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.array_chunks();
    assert_eq!(iter.next().unwrap(), &['l', 'o']);
    assert_eq!(iter.next().unwrap(), &['r', 'e']);
    assert!(iter.next().is_none());
    assert_eq!(iter.remainder(), &['m']);

Run
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#### pub unsafe fn as_chunks_unchecked_mut<const N: usize>( &mut self ) -> &mut [[T; N]]

🔬This is a nightly-only experimental API. (`slice_as_chunks` #74985)

Splits the slice into a slice of `N`-element arrays, assuming that there’s no remainder.

##### Safety

This may only be called when

- The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
- `N != 0`.

##### Examples

    #![feature(slice_as_chunks)]
    let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
    let chunks: &mut [[char; 1]] =
        // SAFETY: 1-element chunks never have remainder
        unsafe { slice.as_chunks_unchecked_mut() };
    chunks[0] = ['L'];
    assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
    let chunks: &mut [[char; 3]] =
        // SAFETY: The slice length (6) is a multiple of 3
        unsafe { slice.as_chunks_unchecked_mut() };
    chunks[1] = ['a', 'x', '?'];
    assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);

    // These would be unsound:
    // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
    // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed

Run
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#### pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T])

🔬This is a nightly-only experimental API. (`slice_as_chunks` #74985)

Splits the slice into a slice of `N`-element arrays, starting at the beginning of the slice, and a remainder slice with length strictly less than `N`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(slice_as_chunks)]
    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    let (chunks, remainder) = v.as_chunks_mut();
    remainder[0] = 9;
    for chunk in chunks {
        *chunk = [count; 2];
        count += 1;
    }
    assert_eq!(v, &[1, 1, 2, 2, 9]);

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#### pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]])

🔬This is a nightly-only experimental API. (`slice_as_chunks` #74985)

Splits the slice into a slice of `N`-element arrays, starting at the end of the slice, and a remainder slice with length strictly less than `N`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(slice_as_chunks)]
    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    let (remainder, chunks) = v.as_rchunks_mut();
    remainder[0] = 9;
    for chunk in chunks {
        *chunk = [count; 2];
        count += 1;
    }
    assert_eq!(v, &[9, 1, 1, 2, 2]);

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#### pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> ⓘ

🔬This is a nightly-only experimental API. (`array_chunks` #74985)

Returns an iterator over `N` elements of the slice at a time, starting at the beginning of the slice.

The chunks are mutable array references and do not overlap. If `N` does not divide the length of the slice, then the last up to `N-1` elements will be omitted and can be retrieved from the `into_remainder` function of the iterator.

This method is the const generic equivalent of `chunks_exact_mut`.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(array_chunks)]
    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    for chunk in v.array_chunks_mut() {
        *chunk = [count; 2];
        count += 1;
    }
    assert_eq!(v, &[1, 1, 2, 2, 0]);

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#### pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> ⓘ

🔬This is a nightly-only experimental API. (`array_windows` #75027)

Returns an iterator over overlapping windows of `N` elements of a slice, starting at the beginning of the slice.

This is the const generic equivalent of `windows`.

If `N` is greater than the size of the slice, it will return no windows.

##### Panics

Panics if `N` is 0. This check will most probably get changed to a compile time error before this method gets stabilized.

##### Examples

    #![feature(array_windows)]
    let slice = [0, 1, 2, 3];
    let mut iter = slice.array_windows();
    assert_eq!(iter.next().unwrap(), &[0, 1]);
    assert_eq!(iter.next().unwrap(), &[1, 2]);
    assert_eq!(iter.next().unwrap(), &[2, 3]);
    assert!(iter.next().is_none());

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1.31.0 · source

#### pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last chunk will not have length `chunk_size`.

See `rchunks_exact` for a variant of this iterator that returns chunks of always exactly `chunk_size` elements, and `chunks` for the same iterator but starting at the beginning of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.rchunks(2);
    assert_eq!(iter.next().unwrap(), &['e', 'm']);
    assert_eq!(iter.next().unwrap(), &['o', 'r']);
    assert_eq!(iter.next().unwrap(), &['l']);
    assert!(iter.next().is_none());

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1.31.0 · source

#### pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end of the slice.

The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the length of the slice, then the last chunk will not have length `chunk_size`.

See `rchunks_exact_mut` for a variant of this iterator that returns chunks of always exactly `chunk_size` elements, and `chunks_mut` for the same iterator but starting at the beginning of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    for chunk in v.rchunks_mut(2) {
        for elem in chunk.iter_mut() {
            *elem += count;
        }
        count += 1;
    }
    assert_eq!(v, &[3, 2, 2, 1, 1]);

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1.31.0 · source

#### pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end of the slice.

The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved from the `remainder` function of the iterator.

Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the resulting code better than in the case of `rchunks`.

See `rchunks` for a variant of this iterator that also returns the remainder as a smaller chunk, and `chunks_exact` for the same iterator but starting at the beginning of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let slice = ['l', 'o', 'r', 'e', 'm'];
    let mut iter = slice.rchunks_exact(2);
    assert_eq!(iter.next().unwrap(), &['e', 'm']);
    assert_eq!(iter.next().unwrap(), &['o', 'r']);
    assert!(iter.next().is_none());
    assert_eq!(iter.remainder(), &['l']);

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1.31.0 · source

#### pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> ⓘ

Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end of the slice.

The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved from the `into_remainder` function of the iterator.

Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the resulting code better than in the case of `chunks_mut`.

See `rchunks_mut` for a variant of this iterator that also returns the remainder as a smaller chunk, and `chunks_exact_mut` for the same iterator but starting at the beginning of the slice.

##### Panics

Panics if `chunk_size` is 0.

##### Examples

    let v = &mut [0, 0, 0, 0, 0];
    let mut count = 1;

    for chunk in v.rchunks_exact_mut(2) {
        for elem in chunk.iter_mut() {
            *elem += count;
        }
        count += 1;
    }
    assert_eq!(v, &[0, 2, 2, 1, 1]);

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#### pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F> ⓘwhere F: FnMut(&T, &T) -> bool,

🔬This is a nightly-only experimental API. (`slice_group_by` #80552)

Returns an iterator over the slice producing non-overlapping runs of elements using the predicate to separate them.

The predicate is called on two elements following themselves, it means the predicate is called on `slice[0]` and `slice[1]` then on `slice[1]` and `slice[2]` and so on.

##### Examples

    #![feature(slice_group_by)]

    let slice = &[1, 1, 1, 3, 3, 2, 2, 2];

    let mut iter = slice.group_by(|a, b| a == b);

    assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
    assert_eq!(iter.next(), Some(&[3, 3][..]));
    assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
    assert_eq!(iter.next(), None);

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This method can be used to extract the sorted subslices:

    #![feature(slice_group_by)]

    let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];

    let mut iter = slice.group_by(|a, b| a <= b);

    assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
    assert_eq!(iter.next(), Some(&[2, 3][..]));
    assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
    assert_eq!(iter.next(), None);

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#### pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F> ⓘwhere F: FnMut(&T, &T) -> bool,

🔬This is a nightly-only experimental API. (`slice_group_by` #80552)

Returns an iterator over the slice producing non-overlapping mutable runs of elements using the predicate to separate them.

The predicate is called on two elements following themselves, it means the predicate is called on `slice[0]` and `slice[1]` then on `slice[1]` and `slice[2]` and so on.

##### Examples

    #![feature(slice_group_by)]

    let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];

    let mut iter = slice.group_by_mut(|a, b| a == b);

    assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
    assert_eq!(iter.next(), Some(&mut [3, 3][..]));
    assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
    assert_eq!(iter.next(), None);

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This method can be used to extract the sorted subslices:

    #![feature(slice_group_by)]

    let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];

    let mut iter = slice.group_by_mut(|a, b| a <= b);

    assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
    assert_eq!(iter.next(), Some(&mut [2, 3][..]));
    assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
    assert_eq!(iter.next(), None);

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#### pub fn split_at(&self, mid: usize) -> (&[T], &[T])

Divides one slice into two at an index.

The first will contain all indices from `[0, mid)` (excluding the index `mid` itself) and the second will contain all indices from `[mid, len)` (excluding the index `len` itself).

##### Panics

Panics if `mid > len`.

##### Examples

    let v = [1, 2, 3, 4, 5, 6];

    {
       let (left, right) = v.split_at(0);
       assert_eq!(left, []);
       assert_eq!(right, [1, 2, 3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_at(2);
        assert_eq!(left, [1, 2]);
        assert_eq!(right, [3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_at(6);
        assert_eq!(left, [1, 2, 3, 4, 5, 6]);
        assert_eq!(right, []);
    }

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#### pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T])

Divides one mutable slice into two at an index.

The first will contain all indices from `[0, mid)` (excluding the index `mid` itself) and the second will contain all indices from `[mid, len)` (excluding the index `len` itself).

##### Panics

Panics if `mid > len`.

##### Examples

    let mut v = [1, 0, 3, 0, 5, 6];
    let (left, right) = v.split_at_mut(2);
    assert_eq!(left, [1, 0]);
    assert_eq!(right, [3, 0, 5, 6]);
    left[1] = 2;
    right[1] = 4;
    assert_eq!(v, [1, 2, 3, 4, 5, 6]);

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#### pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T])

🔬This is a nightly-only experimental API. (`slice_split_at_unchecked` #76014)

Divides one slice into two at an index, without doing bounds checking.

The first will contain all indices from `[0, mid)` (excluding the index `mid` itself) and the second will contain all indices from `[mid, len)` (excluding the index `len` itself).

For a safe alternative see `split_at`.

##### Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that `0 <= mid <= self.len()`.

##### Examples

    #![feature(slice_split_at_unchecked)]

    let v = [1, 2, 3, 4, 5, 6];

    unsafe {
       let (left, right) = v.split_at_unchecked(0);
       assert_eq!(left, []);
       assert_eq!(right, [1, 2, 3, 4, 5, 6]);
    }

    unsafe {
        let (left, right) = v.split_at_unchecked(2);
        assert_eq!(left, [1, 2]);
        assert_eq!(right, [3, 4, 5, 6]);
    }

    unsafe {
        let (left, right) = v.split_at_unchecked(6);
        assert_eq!(left, [1, 2, 3, 4, 5, 6]);
        assert_eq!(right, []);
    }

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#### pub unsafe fn split_at_mut_unchecked( &mut self, mid: usize ) -> (&mut [T], &mut [T])

🔬This is a nightly-only experimental API. (`slice_split_at_unchecked` #76014)

Divides one mutable slice into two at an index, without doing bounds checking.

The first will contain all indices from `[0, mid)` (excluding the index `mid` itself) and the second will contain all indices from `[mid, len)` (excluding the index `len` itself).

For a safe alternative see `split_at_mut`.

##### Safety

Calling this method with an out-of-bounds index is undefined behavior even if the resulting reference is not used. The caller has to ensure that `0 <= mid <= self.len()`.

##### Examples

    #![feature(slice_split_at_unchecked)]

    let mut v = [1, 0, 3, 0, 5, 6];
    // scoped to restrict the lifetime of the borrows
    unsafe {
        let (left, right) = v.split_at_mut_unchecked(2);
        assert_eq!(left, [1, 0]);
        assert_eq!(right, [3, 0, 5, 6]);
        left[1] = 2;
        right[1] = 4;
    }
    assert_eq!(v, [1, 2, 3, 4, 5, 6]);

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#### pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T])

🔬This is a nightly-only experimental API. (`split_array` #90091)

Divides one slice into an array and a remainder slice at an index.

The array will contain all indices from `[0, N)` (excluding the index `N` itself) and the slice will contain all indices from `[N, len)` (excluding the index `len` itself).

##### Panics

Panics if `N > len`.

##### Examples

    #![feature(split_array)]

    let v = &[1, 2, 3, 4, 5, 6][..];

    {
       let (left, right) = v.split_array_ref::<0>();
       assert_eq!(left, &[]);
       assert_eq!(right, [1, 2, 3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_array_ref::<2>();
        assert_eq!(left, &[1, 2]);
        assert_eq!(right, [3, 4, 5, 6]);
    }

    {
        let (left, right) = v.split_array_ref::<6>();
        assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
        assert_eq!(right, []);
    }

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#### pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T])

🔬This is a nightly-only experimental API. (`split_array` #90091)

Divides one mutable slice into an array and a remainder slice at an index.

The array will contain all indices from `[0, N)` (excluding the index `N` itself) and the slice will contain all indices from `[N, len)` (excluding the index `len` itself).

##### Panics

Panics if `N > len`.

##### Examples

    #![feature(split_array)]

    let mut v = &mut [1, 0, 3, 0, 5, 6][..];
    let (left, right) = v.split_array_mut::<2>();
    assert_eq!(left, &mut [1, 0]);
    assert_eq!(right, [3, 0, 5, 6]);
    left[1] = 2;
    right[1] = 4;
    assert_eq!(v, [1, 2, 3, 4, 5, 6]);

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#### pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N])

🔬This is a nightly-only experimental API. (`split_array` #90091)

Divides one slice into an array and a remainder slice at an index from the end.

The slice will contain all indices from `[0, len - N)` (excluding the index `len - N` itself) and the array will contain all indices from `[len - N, len)` (excluding the index `len` itself).

##### Panics

Panics if `N > len`.

##### Examples

    #![feature(split_array)]

    let v = &[1, 2, 3, 4, 5, 6][..];

    {
       let (left, right) = v.rsplit_array_ref::<0>();
       assert_eq!(left, [1, 2, 3, 4, 5, 6]);
       assert_eq!(right, &[]);
    }

    {
        let (left, right) = v.rsplit_array_ref::<2>();
        assert_eq!(left, [1, 2, 3, 4]);
        assert_eq!(right, &[5, 6]);
    }

    {
        let (left, right) = v.rsplit_array_ref::<6>();
        assert_eq!(left, []);
        assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
    }

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#### pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N])

🔬This is a nightly-only experimental API. (`split_array` #90091)

Divides one mutable slice into an array and a remainder slice at an index from the end.

The slice will contain all indices from `[0, len - N)` (excluding the index `N` itself) and the array will contain all indices from `[len - N, len)` (excluding the index `len` itself).

##### Panics

Panics if `N > len`.

##### Examples

    #![feature(split_array)]

    let mut v = &mut [1, 0, 3, 0, 5, 6][..];
    let (left, right) = v.rsplit_array_mut::<4>();
    assert_eq!(left, [1, 0]);
    assert_eq!(right, &mut [3, 0, 5, 6]);
    left[1] = 2;
    right[1] = 4;
    assert_eq!(v, [1, 2, 3, 4, 5, 6]);

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#### pub fn split<F>(&self, pred: F) -> Split<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`. The matched element is not contained in the subslices.

##### Examples

    let slice = [10, 40, 33, 20];
    let mut iter = slice.split(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10, 40]);
    assert_eq!(iter.next().unwrap(), &[20]);
    assert!(iter.next().is_none());

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If the first element is matched, an empty slice will be the first item returned by the iterator. Similarly, if the last element in the slice is matched, an empty slice will be the last item returned by the iterator:

    let slice = [10, 40, 33];
    let mut iter = slice.split(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10, 40]);
    assert_eq!(iter.next().unwrap(), &[]);
    assert!(iter.next().is_none());

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If two matched elements are directly adjacent, an empty slice will be present between them:

    let slice = [10, 6, 33, 20];
    let mut iter = slice.split(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10]);
    assert_eq!(iter.next().unwrap(), &[]);
    assert_eq!(iter.next().unwrap(), &[20]);
    assert!(iter.next().is_none());

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#### pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match `pred`. The matched element is not contained in the subslices.

##### Examples

    let mut v = [10, 40, 30, 20, 60, 50];

    for group in v.split_mut(|num| *num % 3 == 0) {
        group[0] = 1;
    }
    assert_eq!(v, [1, 40, 30, 1, 60, 1]);

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1.51.0 · source

#### pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`. The matched element is contained in the end of the previous subslice as a terminator.

##### Examples

    let slice = [10, 40, 33, 20];
    let mut iter = slice.split_inclusive(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
    assert_eq!(iter.next().unwrap(), &[20]);
    assert!(iter.next().is_none());

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If the last element of the slice is matched, that element will be considered the terminator of the preceding slice. That slice will be the last item returned by the iterator.

    let slice = [3, 10, 40, 33];
    let mut iter = slice.split_inclusive(|num| num % 3 == 0);

    assert_eq!(iter.next().unwrap(), &[3]);
    assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
    assert!(iter.next().is_none());

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1.51.0 · source

#### pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match `pred`. The matched element is contained in the previous subslice as a terminator.

##### Examples

    let mut v = [10, 40, 30, 20, 60, 50];

    for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
        let terminator_idx = group.len()-1;
        group[terminator_idx] = 1;
    }
    assert_eq!(v, [10, 40, 1, 20, 1, 1]);

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1.27.0 · source

#### pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

##### Examples

    let slice = [11, 22, 33, 0, 44, 55];
    let mut iter = slice.rsplit(|num| *num == 0);

    assert_eq!(iter.next().unwrap(), &[44, 55]);
    assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
    assert_eq!(iter.next(), None);

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As with `split()`, if the first or last element is matched, an empty slice will be the first (or last) item returned by the iterator.

    let v = &[0, 1, 1, 2, 3, 5, 8];
    let mut it = v.rsplit(|n| *n % 2 == 0);
    assert_eq!(it.next().unwrap(), &[]);
    assert_eq!(it.next().unwrap(), &[3, 5]);
    assert_eq!(it.next().unwrap(), &[1, 1]);
    assert_eq!(it.next().unwrap(), &[]);
    assert_eq!(it.next(), None);

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1.27.0 · source

#### pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match `pred`, starting at the end of the slice and working backwards. The matched element is not contained in the subslices.

##### Examples

    let mut v = [100, 400, 300, 200, 600, 500];

    let mut count = 0;
    for group in v.rsplit_mut(|num| *num % 3 == 0) {
        count += 1;
        group[0] = count;
    }
    assert_eq!(v, [3, 400, 300, 2, 600, 1]);

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#### pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred`, limited to returning at most `n` items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

##### Examples

Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`, `[20, 60, 50]`):

    let v = [10, 40, 30, 20, 60, 50];

    for group in v.splitn(2, |num| *num % 3 == 0) {
        println!("{group:?}");
    }

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#### pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over mutable subslices separated by elements that match `pred`, limited to returning at most `n` items. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

##### Examples

    let mut v = [10, 40, 30, 20, 60, 50];

    for group in v.splitn_mut(2, |num| *num % 3 == 0) {
        group[0] = 1;
    }
    assert_eq!(v, [1, 40, 30, 1, 60, 50]);

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#### pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred` limited to returning at most `n` items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

##### Examples

Print the slice split once, starting from the end, by numbers divisible by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):

    let v = [10, 40, 30, 20, 60, 50];

    for group in v.rsplitn(2, |num| *num % 3 == 0) {
        println!("{group:?}");
    }

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#### pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F> ⓘwhere F: FnMut(&T) -> bool,

Returns an iterator over subslices separated by elements that match `pred` limited to returning at most `n` items. This starts at the end of the slice and works backwards. The matched element is not contained in the subslices.

The last element returned, if any, will contain the remainder of the slice.

##### Examples

    let mut s = [10, 40, 30, 20, 60, 50];

    for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
        group[0] = 1;
    }
    assert_eq!(s, [1, 40, 30, 20, 60, 1]);

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#### pub fn split_once<F>(&self, pred: F) -> Option<(&[T], &[T])>where F: FnMut(&T) -> bool,

🔬This is a nightly-only experimental API. (`slice_split_once` #112811)

Splits the slice on the first element that matches the specified predicate.

If any matching elements are resent in the slice, returns the prefix before the match and suffix after. The matching element itself is not included. If no elements match, returns `None`.

##### Examples

    #![feature(slice_split_once)]
    let s = [1, 2, 3, 2, 4];
    assert_eq!(s.split_once(|&x| x == 2), Some((
        &[1][..],
        &[3, 2, 4][..]
    )));
    assert_eq!(s.split_once(|&x| x == 0), None);

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#### pub fn rsplit_once<F>(&self, pred: F) -> Option<(&[T], &[T])>where F: FnMut(&T) -> bool,

🔬This is a nightly-only experimental API. (`slice_split_once` #112811)

Splits the slice on the last element that matches the specified predicate.

If any matching elements are resent in the slice, returns the prefix before the match and suffix after. The matching element itself is not included. If no elements match, returns `None`.

##### Examples

    #![feature(slice_split_once)]
    let s = [1, 2, 3, 2, 4];
    assert_eq!(s.rsplit_once(|&x| x == 2), Some((
        &[1, 2, 3][..],
        &[4][..]
    )));
    assert_eq!(s.rsplit_once(|&x| x == 0), None);

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#### pub fn contains(&self, x: &T) -> bool where T: PartialEq,

Returns `true` if the slice contains an element with the given value.

This operation is O(n).

Note that if you have a sorted slice, `binary_search` may be faster.

##### Examples

    let v = [10, 40, 30];
    assert!(v.contains(&30));
    assert!(!v.contains(&50));

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If you do not have a `&T`, but some other value that you can compare with one (for example, `String` implements `PartialEq<str>`), you can use `iter().any`:

    let v = [String::from("hello"), String::from("world")]; // slice of `String`
    assert!(v.iter().any(|e| e == "hello")); // search with `&str`
    assert!(!v.iter().any(|e| e == "hi"));

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#### pub fn starts_with(&self, needle: &[T]) -> bool where T: PartialEq,

Returns `true` if `needle` is a prefix of the slice.

##### Examples

    let v = [10, 40, 30];
    assert!(v.starts_with(&[10]));
    assert!(v.starts_with(&[10, 40]));
    assert!(!v.starts_with(&[50]));
    assert!(!v.starts_with(&[10, 50]));

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Always returns `true` if `needle` is an empty slice:

    let v = &[10, 40, 30];
    assert!(v.starts_with(&[]));
    let v: &[u8] = &[];
    assert!(v.starts_with(&[]));

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#### pub fn ends_with(&self, needle: &[T]) -> bool where T: PartialEq,

Returns `true` if `needle` is a suffix of the slice.

##### Examples

    let v = [10, 40, 30];
    assert!(v.ends_with(&[30]));
    assert!(v.ends_with(&[40, 30]));
    assert!(!v.ends_with(&[50]));
    assert!(!v.ends_with(&[50, 30]));

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Always returns `true` if `needle` is an empty slice:

    let v = &[10, 40, 30];
    assert!(v.ends_with(&[]));
    let v: &[u8] = &[];
    assert!(v.ends_with(&[]));

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1.51.0 · source

#### pub fn strip_prefix<P>(&self, prefix: &P) -> Option<&[T]>where P: SlicePattern<Item = T> + ?Sized, T: PartialEq,

Returns a subslice with the prefix removed.

If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`. If `prefix` is empty, simply returns the original slice.

If the slice does not start with `prefix`, returns `None`.

##### Examples

    let v = &[10, 40, 30];
    assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
    assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
    assert_eq!(v.strip_prefix(&[50]), None);
    assert_eq!(v.strip_prefix(&[10, 50]), None);

    let prefix : &str = "he";
    assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
               Some(b"llo".as_ref()));

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1.51.0 · source

#### pub fn strip_suffix<P>(&self, suffix: &P) -> Option<&[T]>where P: SlicePattern<Item = T> + ?Sized, T: PartialEq,

Returns a subslice with the suffix removed.

If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`. If `suffix` is empty, simply returns the original slice.

If the slice does not end with `suffix`, returns `None`.

##### Examples

    let v = &[10, 40, 30];
    assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
    assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
    assert_eq!(v.strip_suffix(&[50]), None);
    assert_eq!(v.strip_suffix(&[50, 30]), None);

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#### pub fn binary_search(&self, x: &T) -> Result<usize, usize>where T: Ord,

Binary searches this slice for a given element. If the slice is not sorted, the returned result is unspecified and meaningless.

If the value is found then `Result::Ok` is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then `Result::Err` is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also `binary_search_by`, `binary_search_by_key`, and `partition_point`.

##### Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in `[1, 4]`.

    let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

    assert_eq!(s.binary_search(&13),  Ok(9));
    assert_eq!(s.binary_search(&4),   Err(7));
    assert_eq!(s.binary_search(&100), Err(13));
    let r = s.binary_search(&1);
    assert!(match r { Ok(1..=4) => true, _ => false, });

Run

If you want to find that whole range of matching items, rather than an arbitrary matching one, that can be done using `partition_point`:

    let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

    let low = s.partition_point(|x| x < &1);
    assert_eq!(low, 1);
    let high = s.partition_point(|x| x <= &1);
    assert_eq!(high, 5);
    let r = s.binary_search(&1);
    assert!((low..high).contains(&r.unwrap()));

    assert!(s[..low].iter().all(|&x| x < 1));
    assert!(s[low..high].iter().all(|&x| x == 1));
    assert!(s[high..].iter().all(|&x| x > 1));

    // For something not found, the "range" of equal items is empty
    assert_eq!(s.partition_point(|x| x < &11), 9);
    assert_eq!(s.partition_point(|x| x <= &11), 9);
    assert_eq!(s.binary_search(&11), Err(9));

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If you want to insert an item to a sorted vector, while maintaining sort order, consider using `partition_point`:

    let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
    let num = 42;
    let idx = s.partition_point(|&x| x < num);
    // The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);`
    s.insert(idx, num);
    assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

Run
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#### pub fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>where F: FnMut(&'a T) -> Ordering,

Binary searches this slice with a comparator function.

The comparator function should return an order code that indicates whether its argument is `Less`, `Equal` or `Greater` the desired target. If the slice is not sorted or if the comparator function does not implement an order consistent with the sort order of the underlying slice, the returned result is unspecified and meaningless.

If the value is found then `Result::Ok` is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then `Result::Err` is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also `binary_search`, `binary_search_by_key`, and `partition_point`.

##### Examples

Looks up a series of four elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in `[1, 4]`.

    let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];

    let seek = 13;
    assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
    let seek = 4;
    assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
    let seek = 100;
    assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
    let seek = 1;
    let r = s.binary_search_by(|probe| probe.cmp(&seek));
    assert!(match r { Ok(1..=4) => true, _ => false, });

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1.10.0 · source

#### pub fn binary_search_by_key<'a, B, F>( &'a self, b: &B, f: F ) -> Result<usize, usize>where F: FnMut(&'a T) -> B, B: Ord,

Binary searches this slice with a key extraction function.

Assumes that the slice is sorted by the key, for instance with `sort_by_key` using the same key extraction function. If the slice is not sorted by the key, the returned result is unspecified and meaningless.

If the value is found then `Result::Ok` is returned, containing the index of the matching element. If there are multiple matches, then any one of the matches could be returned. The index is chosen deterministically, but is subject to change in future versions of Rust. If the value is not found then `Result::Err` is returned, containing the index where a matching element could be inserted while maintaining sorted order.

See also `binary_search`, `binary_search_by`, and `partition_point`.

##### Examples

Looks up a series of four elements in a slice of pairs sorted by their second elements. The first is found, with a uniquely determined position; the second and third are not found; the fourth could match any position in `[1, 4]`.

    let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
             (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
             (1, 21), (2, 34), (4, 55)];

    assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b),  Ok(9));
    assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b),   Err(7));
    assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
    let r = s.binary_search_by_key(&1, |&(a, b)| b);
    assert!(match r { Ok(1..=4) => true, _ => false, });

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1.20.0 · source

#### pub fn sort_unstable(&mut self)where T: Ord,

Sorts the slice, but might not preserve the order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

##### Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice consists of several concatenated sorted sequences.

##### Examples

    let mut v = [-5, 4, 1, -3, 2];

    v.sort_unstable();
    assert!(v == [-5, -3, 1, 2, 4]);

Run
1.20.0 · source

#### pub fn sort_unstable_by<F>(&mut self, compare: F)where F: FnMut(&T, &T) -> Ordering,

Sorts the slice with a comparator function, but might not preserve the order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(n * log(n)) worst-case.

The comparator function must define a total ordering for the elements in the slice. If the ordering is not total, the order of the elements is unspecified. An order is a total order if it is (for all `a`, `b` and `c`):

- total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
- transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.

For example, while `f64` doesn’t implement `Ord` because `NaN != NaN`, we can use `partial_cmp` as our sort function when we know the slice doesn’t contain a `NaN`.

    let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
    floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
    assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);

Run

##### Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

It is typically faster than stable sorting, except in a few special cases, e.g., when the slice consists of several concatenated sorted sequences.

##### Examples

    let mut v = [5, 4, 1, 3, 2];
    v.sort_unstable_by(|a, b| a.cmp(b));
    assert!(v == [1, 2, 3, 4, 5]);

    // reverse sorting
    v.sort_unstable_by(|a, b| b.cmp(a));
    assert!(v == [5, 4, 3, 2, 1]);

Run
1.20.0 · source

#### pub fn sort_unstable_by_key<K, F>(&mut self, f: F)where F: FnMut(&T) -> K, K: Ord,

Sorts the slice with a key extraction function, but might not preserve the order of equal elements.

This sort is unstable (i.e., may reorder equal elements), in-place (i.e., does not allocate), and O(m * n * log(n)) worst-case, where the key function is O(m).

##### Current implementation

The current algorithm is based on pattern-defeating quicksort by Orson Peters, which combines the fast average case of randomized quicksort with the fast worst case of heapsort, while achieving linear time on slices with certain patterns. It uses some randomization to avoid degenerate cases, but with a fixed seed to always provide deterministic behavior.

Due to its key calling strategy, `sort_unstable_by_key` is likely to be slower than `sort_by_cached_key` in cases where the key function is expensive.

##### Examples

    let mut v = [-5i32, 4, 1, -3, 2];

    v.sort_unstable_by_key(|k| k.abs());
    assert!(v == [1, 2, -3, 4, -5]);

Run
1.49.0 · source

#### pub fn select_nth_unstable( &mut self, index: usize ) -> (&mut [T], &mut T, &mut [T])where T: Ord,

Reorder the slice such that the element at `index` is at its final sorted position.

This reordering has the additional property that any value at position `i < index` will be less than or equal to any value at a position `j > index`. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position `index`), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the reordered slice: the subslice prior to `index`, the element at `index`, and the subslice after `index`; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at `index`.

##### Current implementation

The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also the basis for `sort_unstable`. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

##### Panics

Panics when `index >= len()`, meaning it always panics on empty slices.

##### Examples

    let mut v = [-5i32, 4, 1, -3, 2];

    // Find the median
    v.select_nth_unstable(2);

    // We are only guaranteed the slice will be one of the following, based on the way we sort
    // about the specified index.
    assert!(v == [-3, -5, 1, 2, 4] ||
            v == [-5, -3, 1, 2, 4] ||
            v == [-3, -5, 1, 4, 2] ||
            v == [-5, -3, 1, 4, 2]);

Run
1.49.0 · source

#### pub fn select_nth_unstable_by<F>( &mut self, index: usize, compare: F ) -> (&mut [T], &mut T, &mut [T])where F: FnMut(&T, &T) -> Ordering,

Reorder the slice with a comparator function such that the element at `index` is at its final sorted position.

This reordering has the additional property that any value at position `i < index` will be less than or equal to any value at a position `j > index` using the comparator function. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position `index`), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the slice reordered according to the provided comparator function: the subslice prior to `index`, the element at `index`, and the subslice after `index`; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at `index`.

##### Current implementation

The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also the basis for `sort_unstable`. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

##### Panics

Panics when `index >= len()`, meaning it always panics on empty slices.

##### Examples

    let mut v = [-5i32, 4, 1, -3, 2];

    // Find the median as if the slice were sorted in descending order.
    v.select_nth_unstable_by(2, |a, b| b.cmp(a));

    // We are only guaranteed the slice will be one of the following, based on the way we sort
    // about the specified index.
    assert!(v == [2, 4, 1, -5, -3] ||
            v == [2, 4, 1, -3, -5] ||
            v == [4, 2, 1, -5, -3] ||
            v == [4, 2, 1, -3, -5]);

Run
1.49.0 · source

#### pub fn select_nth_unstable_by_key<K, F>( &mut self, index: usize, f: F ) -> (&mut [T], &mut T, &mut [T])where F: FnMut(&T) -> K, K: Ord,

Reorder the slice with a key extraction function such that the element at `index` is at its final sorted position.

This reordering has the additional property that any value at position `i < index` will be less than or equal to any value at a position `j > index` using the key extraction function. Additionally, this reordering is unstable (i.e. any number of equal elements may end up at position `index`), in-place (i.e. does not allocate), and runs in O(n) time. This function is also known as “kth element” in other libraries.

It returns a triplet of the following from the slice reordered according to the provided key extraction function: the subslice prior to `index`, the element at `index`, and the subslice after `index`; accordingly, the values in those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to the value of the element at `index`.

##### Current implementation

The current algorithm is an introselect implementation based on Pattern Defeating Quicksort, which is also the basis for `sort_unstable`. The fallback algorithm is Median of Medians using Tukey’s Ninther for pivot selection, which guarantees linear runtime for all inputs.

##### Panics

Panics when `index >= len()`, meaning it always panics on empty slices.

##### Examples

    let mut v = [-5i32, 4, 1, -3, 2];

    // Return the median as if the array were sorted according to absolute value.
    v.select_nth_unstable_by_key(2, |a| a.abs());

    // We are only guaranteed the slice will be one of the following, based on the way we sort
    // about the specified index.
    assert!(v == [1, 2, -3, 4, -5] ||
            v == [1, 2, -3, -5, 4] ||
            v == [2, 1, -3, 4, -5] ||
            v == [2, 1, -3, -5, 4]);

Run
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#### pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])where T: PartialEq,

🔬This is a nightly-only experimental API. (`slice_partition_dedup` #54279)

Moves all consecutive repeated elements to the end of the slice according to the `PartialEq` trait implementation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

##### Examples

    #![feature(slice_partition_dedup)]

    let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];

    let (dedup, duplicates) = slice.partition_dedup();

    assert_eq!(dedup, [1, 2, 3, 2, 1]);
    assert_eq!(duplicates, [2, 3, 1]);

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#### pub fn partition_dedup_by<F>(&mut self, same_bucket: F) -> (&mut [T], &mut [T])where F: FnMut(&mut T, &mut T) -> bool,

🔬This is a nightly-only experimental API. (`slice_partition_dedup` #54279)

Moves all but the first of consecutive elements to the end of the slice satisfying a given equality relation.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

The `same_bucket` function is passed references to two elements from the slice and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved at the end of the slice.

If the slice is sorted, the first returned slice contains no duplicates.

##### Examples

    #![feature(slice_partition_dedup)]

    let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];

    let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));

    assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
    assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);

Run
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#### pub fn partition_dedup_by_key<K, F>(&mut self, key: F) -> (&mut [T], &mut [T])where F: FnMut(&mut T) -> K, K: PartialEq,

🔬This is a nightly-only experimental API. (`slice_partition_dedup` #54279)

Moves all but the first of consecutive elements to the end of the slice that resolve to the same key.

Returns two slices. The first contains no consecutive repeated elements. The second contains all the duplicates in no specified order.

If the slice is sorted, the first returned slice contains no duplicates.

##### Examples

    #![feature(slice_partition_dedup)]

    let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];

    let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);

    assert_eq!(dedup, [10, 20, 30, 20, 11]);
    assert_eq!(duplicates, [21, 30, 13]);

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1.26.0 · source

#### pub fn rotate_left(&mut self, mid: usize)

Rotates the slice in-place such that the first `mid` elements of the slice move to the end while the last `self.len() - mid` elements move to the front. After calling `rotate_left`, the element previously at index `mid` will become the first element in the slice.

##### Panics

This function will panic if `mid` is greater than the length of the slice. Note that `mid == self.len()` does not panic and is a no-op rotation.

##### Complexity

Takes linear (in `self.len()`) time.

##### Examples

    let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
    a.rotate_left(2);
    assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);

Run

Rotating a subslice:

    let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
    a[1..5].rotate_left(1);
    assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);

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1.26.0 · source

#### pub fn rotate_right(&mut self, k: usize)

Rotates the slice in-place such that the first `self.len() - k` elements of the slice move to the end while the last `k` elements move to the front. After calling `rotate_right`, the element previously at index `self.len() - k` will become the first element in the slice.

##### Panics

This function will panic if `k` is greater than the length of the slice. Note that `k == self.len()` does not panic and is a no-op rotation.

##### Complexity

Takes linear (in `self.len()`) time.

##### Examples

    let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
    a.rotate_right(2);
    assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);

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Rotating a subslice:

    let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
    a[1..5].rotate_right(1);
    assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);

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1.50.0 · source

#### pub fn fill(&mut self, value: T)where T: Clone,

Fills `self` with elements by cloning `value`.

##### Examples

    let mut buf = vec![0; 10];
    buf.fill(1);
    assert_eq!(buf, vec![1; 10]);

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1.51.0 · source

#### pub fn fill_with<F>(&mut self, f: F)where F: FnMut() -> T,

Fills `self` with elements returned by calling a closure repeatedly.

This method uses a closure to create new values. If you’d rather `Clone` a given value, use `fill`. If you want to use the `Default` trait to generate values, you can pass `Default::default` as the argument.

##### Examples

    let mut buf = vec![1; 10];
    buf.fill_with(Default::default);
    assert_eq!(buf, vec![0; 10]);

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1.7.0 · source

#### pub fn clone_from_slice(&mut self, src: &[T])where T: Clone,

Copies the elements from `src` into `self`.

The length of `src` must be the same as `self`.

##### Panics

This function will panic if the two slices have different lengths.

##### Examples

Cloning two elements from a slice into another:

    let src = [1, 2, 3, 4];
    let mut dst = [0, 0];

    // Because the slices have to be the same length,
    // we slice the source slice from four elements
    // to two. It will panic if we don't do this.
    dst.clone_from_slice(&src[2..]);

    assert_eq!(src, [1, 2, 3, 4]);
    assert_eq!(dst, [3, 4]);

Run

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use `clone_from_slice` on a single slice will result in a compile failure:

ⓘ

    let mut slice = [1, 2, 3, 4, 5];

    slice[..2].clone_from_slice(&slice[3..]); // compile fail!

Run

To work around this, we can use `split_at_mut` to create two distinct sub-slices from a slice:

    let mut slice = [1, 2, 3, 4, 5];

    {
        let (left, right) = slice.split_at_mut(2);
        left.clone_from_slice(&right[1..]);
    }

    assert_eq!(slice, [4, 5, 3, 4, 5]);

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1.9.0 · source

#### pub fn copy_from_slice(&mut self, src: &[T])where T: Copy,

Copies all elements from `src` into `self`, using a memcpy.

The length of `src` must be the same as `self`.

If `T` does not implement `Copy`, use `clone_from_slice`.

##### Panics

This function will panic if the two slices have different lengths.

##### Examples

Copying two elements from a slice into another:

    let src = [1, 2, 3, 4];
    let mut dst = [0, 0];

    // Because the slices have to be the same length,
    // we slice the source slice from four elements
    // to two. It will panic if we don't do this.
    dst.copy_from_slice(&src[2..]);

    assert_eq!(src, [1, 2, 3, 4]);
    assert_eq!(dst, [3, 4]);

Run

Rust enforces that there can only be one mutable reference with no immutable references to a particular piece of data in a particular scope. Because of this, attempting to use `copy_from_slice` on a single slice will result in a compile failure:

ⓘ

    let mut slice = [1, 2, 3, 4, 5];

    slice[..2].copy_from_slice(&slice[3..]); // compile fail!

Run

To work around this, we can use `split_at_mut` to create two distinct sub-slices from a slice:

    let mut slice = [1, 2, 3, 4, 5];

    {
        let (left, right) = slice.split_at_mut(2);
        left.copy_from_slice(&right[1..]);
    }

    assert_eq!(slice, [4, 5, 3, 4, 5]);

Run
1.37.0 · source

#### pub fn copy_within<R>(&mut self, src: R, dest: usize)where R: RangeBounds<usize>, T: Copy,

Copies elements from one part of the slice to another part of itself, using a memmove.

`src` is the range within `self` to copy from. `dest` is the starting index of the range within `self` to copy to, which will have the same length as `src`. The two ranges may overlap. The ends of the two ranges must be less than or equal to `self.len()`.

##### Panics

This function will panic if either range exceeds the end of the slice, or if the end of `src` is before the start.

##### Examples

Copying four bytes within a slice:

    let mut bytes = *b"Hello, World!";

    bytes.copy_within(1..5, 8);

    assert_eq!(&bytes, b"Hello, Wello!");

Run
1.27.0 · source

#### pub fn swap_with_slice(&mut self, other: &mut [T])

Swaps all elements in `self` with those in `other`.

The length of `other` must be the same as `self`.

##### Panics

This function will panic if the two slices have different lengths.

##### Example

Swapping two elements across slices:

    let mut slice1 = [0, 0];
    let mut slice2 = [1, 2, 3, 4];

    slice1.swap_with_slice(&mut slice2[2..]);

    assert_eq!(slice1, [3, 4]);
    assert_eq!(slice2, [1, 2, 0, 0]);

Run

Rust enforces that there can only be one mutable reference to a particular piece of data in a particular scope. Because of this, attempting to use `swap_with_slice` on a single slice will result in a compile failure:

ⓘ

    let mut slice = [1, 2, 3, 4, 5];
    slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!

Run

To work around this, we can use `split_at_mut` to create two distinct mutable sub-slices from a slice:

    let mut slice = [1, 2, 3, 4, 5];

    {
        let (left, right) = slice.split_at_mut(2);
        left.swap_with_slice(&mut right[1..]);
    }

    assert_eq!(slice, [4, 5, 3, 1, 2]);

Run
1.30.0 · source

#### pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T])

Transmute the slice to a slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. How exactly the slice is split up is not specified; the middle part may be smaller than necessary. However, if this fails to return a maximal middle part, that is because code is running in a context where performance does not matter, such as a sanitizer attempting to find alignment bugs. Regular code running in a default (debug or release) execution will return a maximal middle part.

This method has no purpose when either input element `T` or output element `U` are zero-sized and will return the original slice without splitting anything.

##### Safety

This method is essentially a `transmute` with respect to the elements in the returned middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.

##### Examples

Basic usage:

    unsafe {
        let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
        let (prefix, shorts, suffix) = bytes.align_to::<u16>();
        // less_efficient_algorithm_for_bytes(prefix);
        // more_efficient_algorithm_for_aligned_shorts(shorts);
        // less_efficient_algorithm_for_bytes(suffix);
    }

Run
1.30.0 · source

#### pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T])

Transmute the mutable slice to a mutable slice of another type, ensuring alignment of the types is maintained.

This method splits the slice into three distinct slices: prefix, correctly aligned middle slice of a new type, and the suffix slice. How exactly the slice is split up is not specified; the middle part may be smaller than necessary. However, if this fails to return a maximal middle part, that is because code is running in a context where performance does not matter, such as a sanitizer attempting to find alignment bugs. Regular code running in a default (debug or release) execution will return a maximal middle part.

This method has no purpose when either input element `T` or output element `U` are zero-sized and will return the original slice without splitting anything.

##### Safety

This method is essentially a `transmute` with respect to the elements in the returned middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.

##### Examples

Basic usage:

    unsafe {
        let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
        let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
        // less_efficient_algorithm_for_bytes(prefix);
        // more_efficient_algorithm_for_aligned_shorts(shorts);
        // less_efficient_algorithm_for_bytes(suffix);
    }

Run
source

#### pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])where Simd<T, LANES>: AsRef<[T; LANES]>, T: SimdElement, LaneCount<LANES>: SupportedLaneCount,

🔬This is a nightly-only experimental API. (`portable_simd` #86656)

Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.

This is a safe wrapper around `slice::align_to`, so has the same weak postconditions as that method. You’re only assured that `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.

Notably, all of the following are possible:

- `prefix.len() >= LANES`.
- `middle.is_empty()` despite `self.len() >= 3 * LANES`.
- `suffix.len() >= LANES`.

That said, this is a safe method, so if you’re only writing safe code, then this can at most cause incorrect logic, not unsoundness.

##### Panics

This will panic if the size of the SIMD type is different from `LANES` times that of the scalar.

At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like `LANES == 3`.

##### Examples

    #![feature(portable_simd)]
    use core::simd::SimdFloat;

    let short = &[1, 2, 3];
    let (prefix, middle, suffix) = short.as_simd::<4>();
    assert_eq!(middle, []); // Not enough elements for anything in the middle

    // They might be split in any possible way between prefix and suffix
    let it = prefix.iter().chain(suffix).copied();
    assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);

    fn basic_simd_sum(x: &[f32]) -> f32 {
        use std::ops::Add;
        use std::simd::f32x4;
        let (prefix, middle, suffix) = x.as_simd();
        let sums = f32x4::from_array([
            prefix.iter().copied().sum(),
            0.0,
            0.0,
            suffix.iter().copied().sum(),
        ]);
        let sums = middle.iter().copied().fold(sums, f32x4::add);
        sums.reduce_sum()
    }

    let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
    assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);

Run
source

#### pub fn as_simd_mut<const LANES: usize>( &mut self ) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])where Simd<T, LANES>: AsMut<[T; LANES]>, T: SimdElement, LaneCount<LANES>: SupportedLaneCount,

🔬This is a nightly-only experimental API. (`portable_simd` #86656)

Split a mutable slice into a mutable prefix, a middle of aligned SIMD types, and a mutable suffix.

This is a safe wrapper around `slice::align_to_mut`, so has the same weak postconditions as that method. You’re only assured that `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.

Notably, all of the following are possible:

- `prefix.len() >= LANES`.
- `middle.is_empty()` despite `self.len() >= 3 * LANES`.
- `suffix.len() >= LANES`.

That said, this is a safe method, so if you’re only writing safe code, then this can at most cause incorrect logic, not unsoundness.

This is the mutable version of `slice::as_simd`; see that for examples.

##### Panics

This will panic if the size of the SIMD type is different from `LANES` times that of the scalar.

At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps that from ever happening, as only power-of-two numbers of lanes are supported. It’s possible that, in the future, those restrictions might be lifted in a way that would make it possible to see panics from this method for something like `LANES == 3`.

source

#### pub fn is_sorted(&self) -> bool where T: PartialOrd,

🔬This is a nightly-only experimental API. (`is_sorted` #53485)

Checks if the elements of this slice are sorted.

That is, for each element `a` and its following element `b`, `a <= b` must hold. If the slice yields exactly zero or one element, `true` is returned.

Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition implies that this function returns `false` if any two consecutive items are not comparable.

##### Examples

    #![feature(is_sorted)]
    let empty: [i32; 0] = [];

    assert!([1, 2, 2, 9].is_sorted());
    assert!(![1, 3, 2, 4].is_sorted());
    assert!([0].is_sorted());
    assert!(empty.is_sorted());
    assert!(![0.0, 1.0, f32::NAN].is_sorted());

Run
source

#### pub fn is_sorted_by<'a, F>(&'a self, compare: F) -> bool where F: FnMut(&'a T, &'a T) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (`is_sorted` #53485)

Checks if the elements of this slice are sorted using the given comparator function.

Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` function to determine the ordering of two elements. Apart from that, it’s equivalent to `is_sorted`; see its documentation for more information.

source

#### pub fn is_sorted_by_key<'a, F, K>(&'a self, f: F) -> bool where F: FnMut(&'a T) -> K, K: PartialOrd,

🔬This is a nightly-only experimental API. (`is_sorted` #53485)

Checks if the elements of this slice are sorted using the given key extraction function.

Instead of comparing the slice’s elements directly, this function compares the keys of the elements, as determined by `f`. Apart from that, it’s equivalent to `is_sorted`; see its documentation for more information.

##### Examples

    #![feature(is_sorted)]

    assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
    assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));

Run
1.52.0 · source

#### pub fn partition_point<P>(&self, pred: P) -> usize where P: FnMut(&T) -> bool,

Returns the index of the partition point according to the given predicate (the index of the first element of the second partition).

The slice is assumed to be partitioned according to the given predicate. This means that all elements for which the predicate returns true are at the start of the slice and all elements for which the predicate returns false are at the end. For example, `[7, 15, 3, 5, 4, 12, 6]` is partitioned under the predicate `x % 2 != 0` (all odd numbers are at the start, all even at the end).

If this slice is not partitioned, the returned result is unspecified and meaningless, as this method performs a kind of binary search.

See also `binary_search`, `binary_search_by`, and `binary_search_by_key`.

##### Examples

    let v = [1, 2, 3, 3, 5, 6, 7];
    let i = v.partition_point(|&x| x < 5);

    assert_eq!(i, 4);
    assert!(v[..i].iter().all(|&x| x < 5));
    assert!(v[i..].iter().all(|&x| !(x < 5)));

Run

If all elements of the slice match the predicate, including if the slice is empty, then the length of the slice will be returned:

    let a = [2, 4, 8];
    assert_eq!(a.partition_point(|x| x < &100), a.len());
    let a: [i32; 0] = [];
    assert_eq!(a.partition_point(|x| x < &100), 0);

Run

If you want to insert an item to a sorted vector, while maintaining sort order:

    let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
    let num = 42;
    let idx = s.partition_point(|&x| x < num);
    s.insert(idx, num);
    assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);

Run
source

#### pub fn take<R, 'a>(self: &mut &'a [T], range: R) -> Option<&'a [T]>where R: OneSidedRange<usize>,

🔬This is a nightly-only experimental API. (`slice_take` #62280)

Removes the subslice corresponding to the given range and returns a reference to it.

Returns `None` and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as `2..` or `..6`, but not `2..6`.

##### Examples

Taking the first three elements of a slice:

    #![feature(slice_take)]

    let mut slice: &[_] = &['a', 'b', 'c', 'd'];
    let mut first_three = slice.take(..3).unwrap();

    assert_eq!(slice, &['d']);
    assert_eq!(first_three, &['a', 'b', 'c']);

Run

Taking the last two elements of a slice:

    #![feature(slice_take)]

    let mut slice: &[_] = &['a', 'b', 'c', 'd'];
    let mut tail = slice.take(2..).unwrap();

    assert_eq!(slice, &['a', 'b']);
    assert_eq!(tail, &['c', 'd']);

Run

Getting `None` when `range` is out of bounds:

    #![feature(slice_take)]

    let mut slice: &[_] = &['a', 'b', 'c', 'd'];

    assert_eq!(None, slice.take(5..));
    assert_eq!(None, slice.take(..5));
    assert_eq!(None, slice.take(..=4));
    let expected: &[char] = &['a', 'b', 'c', 'd'];
    assert_eq!(Some(expected), slice.take(..4));

Run
source

#### pub fn take_mut<R, 'a>(self: &mut &'a mut [T], range: R) -> Option<&'a mut [T]>where R: OneSidedRange<usize>,

🔬This is a nightly-only experimental API. (`slice_take` #62280)

Removes the subslice corresponding to the given range and returns a mutable reference to it.

Returns `None` and does not modify the slice if the given range is out of bounds.

Note that this method only accepts one-sided ranges such as `2..` or `..6`, but not `2..6`.

##### Examples

Taking the first three elements of a slice:

    #![feature(slice_take)]

    let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
    let mut first_three = slice.take_mut(..3).unwrap();

    assert_eq!(slice, &mut ['d']);
    assert_eq!(first_three, &mut ['a', 'b', 'c']);

Run

Taking the last two elements of a slice:

    #![feature(slice_take)]

    let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
    let mut tail = slice.take_mut(2..).unwrap();

    assert_eq!(slice, &mut ['a', 'b']);
    assert_eq!(tail, &mut ['c', 'd']);

Run

Getting `None` when `range` is out of bounds:

    #![feature(slice_take)]

    let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];

    assert_eq!(None, slice.take_mut(5..));
    assert_eq!(None, slice.take_mut(..5));
    assert_eq!(None, slice.take_mut(..=4));
    let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
    assert_eq!(Some(expected), slice.take_mut(..4));

Run
source

#### pub fn take_first<'a>(self: &mut &'a [T]) -> Option<&'a T>

🔬This is a nightly-only experimental API. (`slice_take` #62280)

Removes the first element of the slice and returns a reference to it.

Returns `None` if the slice is empty.

##### Examples

    #![feature(slice_take)]

    let mut slice: &[_] = &['a', 'b', 'c'];
    let first = slice.take_first().unwrap();

    assert_eq!(slice, &['b', 'c']);
    assert_eq!(first, &'a');

Run
source

#### pub fn take_first_mut<'a>(self: &mut &'a mut [T]) -> Option<&'a mut T>

🔬This is a nightly-only experimental API. (`slice_take` #62280)

Removes the first element of the slice and returns a mutable reference to it.

Returns `None` if the slice is empty.

##### Examples

    #![feature(slice_take)]

    let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
    let first = slice.take_first_mut().unwrap();
    *first = 'd';

    assert_eq!(slice, &['b', 'c']);
    assert_eq!(first, &'d');

Run
source

#### pub fn take_last<'a>(self: &mut &'a [T]) -> Option<&'a T>

🔬This is a nightly-only experimental API. (`slice_take` #62280)

Removes the last element of the slice and returns a reference to it.

Returns `None` if the slice is empty.

##### Examples

    #![feature(slice_take)]

    let mut slice: &[_] = &['a', 'b', 'c'];
    let last = slice.take_last().unwrap();

    assert_eq!(slice, &['a', 'b']);
    assert_eq!(last, &'c');

Run
source

#### pub fn take_last_mut<'a>(self: &mut &'a mut [T]) -> Option<&'a mut T>

🔬This is a nightly-only experimental API. (`slice_take` #62280)

Removes the last element of the slice and returns a mutable reference to it.

Returns `None` if the slice is empty.

##### Examples

    #![feature(slice_take)]

    let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
    let last = slice.take_last_mut().unwrap();
    *last = 'd';

    assert_eq!(slice, &['a', 'b']);
    assert_eq!(last, &'d');

Run
source

#### pub unsafe fn get_many_unchecked_mut<const N: usize>( &mut self, indices: [usize; N] ) -> [&mut T; N]

🔬This is a nightly-only experimental API. (`get_many_mut` #104642)

Returns mutable references to many indices at once, without doing any checks.

For a safe alternative see `get_many_mut`.

##### Safety

Calling this method with overlapping or out-of-bounds indices is undefined behavior even if the resulting references are not used.

##### Examples

    #![feature(get_many_mut)]

    let x = &mut [1, 2, 4];

    unsafe {
        let [a, b] = x.get_many_unchecked_mut([0, 2]);
        *a *= 10;
        *b *= 100;
    }
    assert_eq!(x, &[10, 2, 400]);

Run
source

#### pub fn get_many_mut<const N: usize>( &mut self, indices: [usize; N] ) -> Result<[&mut T; N], GetManyMutError<N>>

🔬This is a nightly-only experimental API. (`get_many_mut` #104642)

Returns mutable references to many indices at once.

Returns an error if any index is out-of-bounds, or if the same index was passed more than once.

##### Examples

    #![feature(get_many_mut)]

    let v = &mut [1, 2, 3];
    if let Ok([a, b]) = v.get_many_mut([0, 2]) {
        *a = 413;
        *b = 612;
    }
    assert_eq!(v, &[413, 2, 612]);

Run
source

#### pub fn as_str(&self) -> &str

🔬This is a nightly-only experimental API. (`ascii_char` #110998)

Views this slice of ASCII characters as a UTF-8 `str`.

source

#### pub fn as_bytes(&self) -> &[u8]

🔬This is a nightly-only experimental API. (`ascii_char` #110998)

Views this slice of ASCII characters as a slice of `u8` bytes.

source

#### pub fn sort_floats(&mut self)

🔬This is a nightly-only experimental API. (`sort_floats` #93396)

Sorts the slice of floats.

This sort is in-place (i.e. does not allocate), O(n * log(n)) worst-case, and uses the ordering defined by `f32::total_cmp`.

##### Current implementation

This uses the same sorting algorithm as `sort_unstable_by`.

##### Examples

    #![feature(sort_floats)]
    let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];

    v.sort_floats();
    let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
    assert_eq!(&v[..8], &sorted[..8]);
    assert!(v[8].is_nan());

Run

## Trait Implementations§

1.5.0 · source§

### impl<T, A: Allocator, FH: FailureHandling> AsMut<[T]> for Vec<T, A, FH>

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#### fn as_mut(&mut self) -> &mut [T]

Converts this type into a mutable reference of the (usually inferred) input type.
1.5.0 · source§

### impl<T, A: Allocator, FH: FailureHandling> AsMut<Vec<T, A, FH>> for Vec<T, A, FH>

source§

#### fn as_mut(&mut self) -> &mut Vec<T, A, FH>

Converts this type into a mutable reference of the (usually inferred) input type.
source§

### impl<T, A: Allocator, FH: FailureHandling> AsRef<[T]> for Vec<T, A, FH>

source§

#### fn as_ref(&self) -> &[T]

Converts this type into a shared reference of the (usually inferred) input type.
source§

### impl<T, A: Allocator, FH: FailureHandling> AsRef<Vec<T, A, FH>> for Vec<T, A, FH>

source§

#### fn as_ref(&self) -> &Vec<T, A, FH>

Converts this type into a shared reference of the (usually inferred) input type.
source§

### impl<T, A: Allocator> Borrow<[T]> for Vec<T, A>

source§

#### fn borrow(&self) -> &[T]

Immutably borrows from an owned value. Read more
source§

### impl<T, A: Allocator> BorrowMut<[T]> for Vec<T, A>

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#### fn borrow_mut(&mut self) -> &mut [T]

Mutably borrows from an owned value. Read more
source§

### impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A, Fatal>

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#### fn clone(&self) -> Self

Returns a copy of the value. Read more
source§

#### fn clone_from(&mut self, other: &Self)

Performs copy-assignment from `source`. Read more
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### impl<T: Debug, A: Allocator, FH: FailureHandling> Debug for Vec<T, A, FH>

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

### impl<T> Default for Vec<T>

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#### fn default() -> Vec<T>

Creates an empty `Vec<T>`.

The vector will not allocate until elements are pushed onto it.

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### impl<T, A: Allocator, FH: FailureHandling> Deref for Vec<T, A, FH>

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#### type Target = [T]

The resulting type after dereferencing.
source§

#### fn deref(&self) -> &[T]

Dereferences the value.
source§

### impl<T, A: Allocator, FH: FailureHandling> DerefMut for Vec<T, A, FH>

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#### fn deref_mut(&mut self) -> &mut [T]

Mutably dereferences the value.
source§

### impl<T, A: Allocator, FH: FailureHandling> Drop for Vec<T, A, FH>

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#### fn drop(&mut self)

Executes the destructor for this type. Read more
1.2.0 · source§

### impl<'a, T: Copy + 'a, A: Allocator> Extend<&'a T> for Vec<T, A, Fatal>

Extend implementation that copies elements out of references before pushing them onto the Vec.

This implementation is specialized for slice iterators, where it uses `copy_from_slice` to append the entire slice at once.

source§

#### fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator. Read more
source§

#### fn extend_one(&mut self, item: &'a T)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
source§

### impl<T, A: Allocator> Extend<T> for Vec<T, A, Fatal>

source§

#### fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator. Read more
source§

#### fn extend_one(&mut self, item: T)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
source§

### impl<T: Clone> From<&[T]> for Vec<T>

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#### fn from(s: &[T]) -> Vec<T>

Allocate a `Vec<T>` and fill it by cloning `s`’s items.

##### Examples

    assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);

Run
1.74.0 · source§

### impl<T: Clone, const N: usize> From<&[T; N]> for Vec<T>

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#### fn from(s: &[T; N]) -> Vec<T>

Allocate a `Vec<T>` and fill it by cloning `s`’s items.

##### Examples

    assert_eq!(Vec::from(&[1, 2, 3]), vec![1, 2, 3]);

Run
1.28.0 · source§

### impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]>

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#### fn from(v: &'a Vec<T>) -> Cow<'a, [T]>

Creates a `Borrowed` variant of `Cow` from a reference to `Vec`.

This conversion does not allocate or clone the data.

1.19.0 · source§

### impl<T: Clone> From<&mut [T]> for Vec<T>

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#### fn from(s: &mut [T]) -> Vec<T>

Allocate a `Vec<T>` and fill it by cloning `s`’s items.

##### Examples

    assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);

Run
1.74.0 · source§

### impl<T: Clone, const N: usize> From<&mut [T; N]> for Vec<T>

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#### fn from(s: &mut [T; N]) -> Vec<T>

Allocate a `Vec<T>` and fill it by cloning `s`’s items.

##### Examples

    assert_eq!(Vec::from(&mut [1, 2, 3]), vec![1, 2, 3]);

Run
source§

### impl From<&str> for Vec<u8>

source§

#### fn from(s: &str) -> Vec<u8>

Allocate a `Vec<u8>` and fill it with a UTF-8 string.

##### Examples

    assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);

Run
1.44.0 · source§

### impl<T, const N: usize> From<[T; N]> for Vec<T>

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#### fn from(s: [T; N]) -> Vec<T>

Allocate a `Vec<T>` and move `s`’s items into it.

##### Examples

    assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);

Run
1.5.0 · source§

### impl<T, A: Allocator> From<BinaryHeap<T, A>> for Vec<T, A>

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#### fn from(heap: BinaryHeap<T, A>) -> Vec<T, A>

Converts a `BinaryHeap<T>` into a `Vec<T>`.

This conversion requires no data movement or allocation, and has constant time complexity.

1.18.0 · source§

### impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A>

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#### fn from(s: Box<[T], A>) -> Self

Convert a boxed slice into a vector by transferring ownership of the existing heap allocation.

##### Examples

    let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
    assert_eq!(Vec::from(b), vec![1, 2, 3]);

Run
1.7.0 · source§

### impl From<CString> for Vec<u8>

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#### fn from(s: CString) -> Vec<u8>

Converts a `CString` into a `Vec<u8>`.

The conversion consumes the `CString`, and removes the terminating NUL byte.

1.14.0 · source§

### impl<'a, T> From<Cow<'a, [T]>> for Vec<T>where [T]: ToOwned<Owned = Vec<T>>,

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#### fn from(s: Cow<'a, [T]>) -> Vec<T>

Convert a clone-on-write slice into a vector.

If `s` already owns a `Vec<T>`, it will be returned directly. If `s` is borrowing a slice, a new `Vec<T>` will be allocated and filled by cloning `s`’s items into it.

##### Examples

    let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
    let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
    assert_eq!(Vec::from(o), Vec::from(b));

Run
1.14.0 · source§

### impl From<String> for Vec<u8>

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#### fn from(string: String) -> Vec<u8>

Converts the given `String` to a vector `Vec` that holds values of type `u8`.

##### Examples

    let s1 = String::from("hello world");
    let v1 = Vec::from(s1);

    for b in v1 {
        println!("{b}");
    }

Run
1.43.0 · source§

### impl From<Vec<NonZeroU8>> for CString

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#### fn from(v: Vec<NonZeroU8>) -> CString

Converts a `Vec<NonZeroU8>` into a `CString` without copying nor checking for inner null bytes.

1.8.0 · source§

### impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>

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#### fn from(v: Vec<T>) -> Cow<'a, [T]>

Creates an `Owned` variant of `Cow` from an owned instance of `Vec`.

This conversion does not allocate or clone the data.

1.21.0 · source§

### impl<T, A: Allocator + Clone> From<Vec<T, A>> for Arc<[T], A>

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#### fn from(v: Vec<T, A>) -> Arc<[T], A>

Allocate a reference-counted slice and move `v`’s items into it.

##### Example

    let unique: Vec<i32> = vec![1, 2, 3];
    let shared: Arc<[i32]> = Arc::from(unique);
    assert_eq!(&[1, 2, 3], &shared[..]);

Run
1.5.0 · source§

### impl<T: Ord, A: Allocator> From<Vec<T, A>> for BinaryHeap<T, A>

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#### fn from(vec: Vec<T, A>) -> BinaryHeap<T, A>

Converts a `Vec<T>` into a `BinaryHeap<T>`.

This conversion happens in-place, and has O(n) time complexity.

1.20.0 · source§

### impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A>

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#### fn from(v: Vec<T, A>) -> Self

Convert a vector into a boxed slice.

If `v` has excess capacity, its items will be moved into a newly-allocated buffer with exactly the right capacity.

##### Examples

    assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());

Run

Any excess capacity is removed:

    let mut vec = Vec::with_capacity(10);
    vec.extend([1, 2, 3]);

    assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());

Run
1.21.0 · source§

### impl<T, A: Allocator> From<Vec<T, A>> for Rc<[T], A>

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#### fn from(v: Vec<T, A>) -> Rc<[T], A>

Allocate a reference-counted slice and move `v`’s items into it.

##### Example

    let unique: Vec<i32> = vec![1, 2, 3];
    let shared: Rc<[i32]> = Rc::from(unique);
    assert_eq!(&[1, 2, 3], &shared[..]);

Run
1.10.0 · source§

### impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A>

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#### fn from(other: Vec<T, A>) -> Self

Turn a `Vec<T>` into a `VecDeque<T>`.

This conversion is guaranteed to run in O(1) time and to not re-allocate the `Vec`’s buffer or allocate any additional memory.

1.10.0 · source§

### impl<T, A: Allocator> From<VecDeque<T, A>> for Vec<T, A>

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#### fn from(other: VecDeque<T, A>) -> Self

Turn a `VecDeque<T>` into a `Vec<T>`.

This never needs to re-allocate, but does need to do O(n) data movement if the circular buffer doesn’t happen to be at the beginning of the allocation.

##### Examples

    use std::collections::VecDeque;

    // This one is *O*(1).
    let deque: VecDeque<_> = (1..5).collect();
    let ptr = deque.as_slices().0.as_ptr();
    let vec = Vec::from(deque);
    assert_eq!(vec, [1, 2, 3, 4]);
    assert_eq!(vec.as_ptr(), ptr);

    // This one needs data rearranging.
    let mut deque: VecDeque<_> = (1..5).collect();
    deque.push_front(9);
    deque.push_front(8);
    let ptr = deque.as_slices().1.as_ptr();
    let vec = Vec::from(deque);
    assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
    assert_eq!(vec.as_ptr(), ptr);

Run
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### impl<T> FromIterator<T> for Vec<T>

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#### fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T>

Creates a value from an iterator. Read more
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### impl<T: Hash, A: Allocator, FH: FailureHandling> Hash for Vec<T, A, FH>

The hash of a vector is the same as that of the corresponding slice, as required by the `core::borrow::Borrow` implementation.

    use std::hash::BuildHasher;

    let b = std::collections::hash_map::RandomState::new();
    let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
    let s: &[u8] = &[0xa8, 0x3c, 0x09];
    assert_eq!(b.hash_one(v), b.hash_one(s));

Run
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#### fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given `Hasher`. Read more
1.3.0 · source§

#### fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl<T, I: SliceIndex<[T]>, A: Allocator, FH: FailureHandling> Index<I> for Vec<T, A, FH>

§

#### type Output = <I as SliceIndex<[T]>>::Output

The returned type after indexing.
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#### fn index(&self, index: I) -> &Self::Output

Performs the indexing (`container[index]`) operation. Read more
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### impl<T, I: SliceIndex<[T]>, A: Allocator, FH: FailureHandling> IndexMut<I> for Vec<T, A, FH>

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#### fn index_mut(&mut self, index: I) -> &mut Self::Output

Performs the mutable indexing (`container[index]`) operation. Read more
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### impl<'a, T, A: Allocator, FH: FailureHandling> IntoIterator for &'a Vec<T, A, FH>

§

#### type Item = &'a T

The type of the elements being iterated over.
§

#### type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?
source§

#### fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value. Read more
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### impl<'a, T, A: Allocator, FH: FailureHandling> IntoIterator for &'a mut Vec<T, A, FH>

§

#### type Item = &'a mut T

The type of the elements being iterated over.
§

#### type IntoIter = IterMut<'a, T>

Which kind of iterator are we turning this into?
source§

#### fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value. Read more
source§

### impl<T, A: Allocator, FH: FailureHandling> IntoIterator for Vec<T, A, FH>

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#### fn into_iter(self) -> Self::IntoIter

Creates a consuming iterator, that is, one that moves each value out of the vector (from start to end). The vector cannot be used after calling this.

##### Examples

    let v = vec!["a".to_string(), "b".to_string()];
    let mut v_iter = v.into_iter();

    let first_element: Option<String> = v_iter.next();

    assert_eq!(first_element, Some("a".to_string()));
    assert_eq!(v_iter.next(), Some("b".to_string()));
    assert_eq!(v_iter.next(), None);

Run
§

#### type Item = T

The type of the elements being iterated over.
§

#### type IntoIter = IntoIter<T, A>

Which kind of iterator are we turning this into?
source§

### impl<T: Ord, A: Allocator, FH: FailureHandling> Ord for Vec<T, A, FH>

Implements ordering of vectors, lexicographically.

source§

#### fn cmp(&self, other: &Self) -> Ordering

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · source§

#### fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · source§

#### fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · source§

#### fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<&[U]> for Vec<T, A, FH>where T: PartialEq<U>,

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#### fn eq(&self, other: &&[U]) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &&[U]) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl<T, U, A: Allocator, FH: FailureHandling, const N: usize> PartialEq<&[U; N]> for Vec<T, A, FH>where T: PartialEq<U>,

source§

#### fn eq(&self, other: &&[U; N]) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &&[U; N]) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<&mut [U]> for Vec<T, A, FH>where T: PartialEq<U>,

source§

#### fn eq(&self, other: &&mut [U]) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &&mut [U]) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.48.0 · source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<[U]> for Vec<T, A, FH>where T: PartialEq<U>,

source§

#### fn eq(&self, other: &[U]) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &[U]) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl<T, U, A: Allocator, FH: FailureHandling, const N: usize> PartialEq<[U; N]> for Vec<T, A, FH>where T: PartialEq<U>,

source§

#### fn eq(&self, other: &[U; N]) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &[U; N]) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.17.0 · source§

### impl<T, U, A: Allocator> PartialEq<Vec<U, A>> for VecDeque<T, A>where T: PartialEq<U>,

source§

#### fn eq(&self, other: &Vec<U, A>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &Rhs) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.46.0 · source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<Vec<U, A, FH>> for &[T]where T: PartialEq<U>,

source§

#### fn eq(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.46.0 · source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<Vec<U, A, FH>> for &mut [T]where T: PartialEq<U>,

source§

#### fn eq(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.48.0 · source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<Vec<U, A, FH>> for [T]where T: PartialEq<U>,

source§

#### fn eq(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl<T, U, A: Allocator, FH: FailureHandling> PartialEq<Vec<U, A, FH>> for Cow<'_, [T]>where T: PartialEq<U> + Clone,

source§

#### fn eq(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &Vec<U, A, FH>) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl<T, U, A1: Allocator, A2: Allocator, FH1: FailureHandling, FH2: FailureHandling> PartialEq<Vec<U, A2, FH2>> for Vec<T, A1, FH1>where T: PartialEq<U>,

source§

#### fn eq(&self, other: &Vec<U, A2, FH2>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
source§

#### fn ne(&self, other: &Vec<U, A2, FH2>) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl<T, A1, A2, FH1, FH2> PartialOrd<Vec<T, A2, FH2>> for Vec<T, A1, FH1>where T: PartialOrd, A1: Allocator, A2: Allocator, FH1: FailureHandling, FH2: FailureHandling,

Implements comparison of vectors, lexicographically.

source§

#### fn partial_cmp(&self, other: &Vec<T, A2, FH2>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
source§

#### fn lt(&self, other: &Rhs) -> bool

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more
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#### fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
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#### fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
source§

#### fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
1.66.0 · source§

### impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]>

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#### fn try_from(vec: Vec<T>) -> Result<Self, Self::Error>

Attempts to convert a `Vec<T>` into a `Box<[T; N]>`.

Like `Vec::into_boxed_slice`, this is in-place if `vec.capacity() == N`, but will require a reallocation otherwise.

##### Errors

Returns the original `Vec<T>` in the `Err` variant if `boxed_slice.len()` does not equal `N`.

##### Examples

This can be used with `vec!` to create an array on the heap:

    let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap();
    assert_eq!(state.len(), 100);

Run
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#### type Error = Vec<T>

The type returned in the event of a conversion error.
1.48.0 · source§

### impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N]

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#### fn try_from(vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>>

Gets the entire contents of the `Vec<T>` as an array, if its size exactly matches that of the requested array.

##### Examples

    assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
    assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));

Run

If the length doesn’t match, the input comes back in `Err`:

    let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
    assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));

Run

If you’re fine with just getting a prefix of the `Vec<T>`, you can call `.truncate(N)` first.

    let mut v = String::from("hello world").into_bytes();
    v.sort();
    v.truncate(2);
    let [a, b]: [_; 2] = v.try_into().unwrap();
    assert_eq!(a, b' ');
    assert_eq!(b, b'd');

Run
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#### type Error = Vec<T, A>

The type returned in the event of a conversion error.
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### impl<T: Eq, A: Allocator, FH: FailureHandling> Eq for Vec<T, A, FH>

## Auto Trait Implementations§

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### impl<T, A, FH> RefUnwindSafe for Vec<T, A, FH>where A: RefUnwindSafe, FH: RefUnwindSafe, T: RefUnwindSafe,

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### impl<T, A, FH> Send for Vec<T, A, FH>where A: Send, T: Send,

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### impl<T, A, FH> Sync for Vec<T, A, FH>where A: Sync, T: Sync,

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### impl<T, A, FH> Unpin for Vec<T, A, FH>where A: Unpin, T: Unpin,

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### impl<T, A, FH> UnwindSafe for Vec<T, A, FH>where A: UnwindSafe, FH: UnwindSafe, T: UnwindSafe,

## Blanket Implementations§

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### impl<T> Any for Twhere T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for Twhere U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.