# Struct alloc::rc::Rc

1.0.0 · source ·

    pub struct Rc<T: ?Sized, A: Allocator = Global> { /* private fields */ }

Expand description

A single-threaded reference-counting pointer. ‘Rc’ stands for ‘Reference Counted’.

See the module-level documentation for more details.

The inherent methods of `Rc` are all associated functions, which means that you have to call them as e.g., `Rc::get_mut(&mut value)` instead of `value.get_mut()`. This avoids conflicts with methods of the inner type `T`.

## Implementations§

source§

### impl<T> Rc<T>

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#### pub fn new(value: T) -> Rc<T>

Constructs a new `Rc<T>`.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

Run
1.60.0 · source

#### pub fn new_cyclic<F>(data_fn: F) -> Rc<T>where F: FnOnce(&Weak<T>) -> T,

Constructs a new `Rc<T>` while giving you a `Weak<T>` to the allocation, to allow you to construct a `T` which holds a weak pointer to itself.

Generally, a structure circularly referencing itself, either directly or indirectly, should not hold a strong reference to itself to prevent a memory leak. Using this function, you get access to the weak pointer during the initialization of `T`, before the `Rc<T>` is created, such that you can clone and store it inside the `T`.

`new_cyclic` first allocates the managed allocation for the `Rc<T>`, then calls your closure, giving it a `Weak<T>` to this allocation, and only afterwards completes the construction of the `Rc<T>` by placing the `T` returned from your closure into the allocation.

Since the new `Rc<T>` is not fully-constructed until `Rc<T>::new_cyclic` returns, calling `upgrade` on the weak reference inside your closure will fail and result in a `None` value.

##### Panics

If `data_fn` panics, the panic is propagated to the caller, and the temporary `Weak<T>` is dropped normally.

##### Examples

    use std::rc::{Rc, Weak};

    struct Gadget {
        me: Weak<Gadget>,
    }

    impl Gadget {
        /// Construct a reference counted Gadget.
        fn new() -> Rc<Self> {
            // `me` is a `Weak<Gadget>` pointing at the new allocation of the
            // `Rc` we're constructing.
            Rc::new_cyclic(|me| {
                // Create the actual struct here.
                Gadget { me: me.clone() }
            })
        }

        /// Return a reference counted pointer to Self.
        fn me(&self) -> Rc<Self> {
            self.me.upgrade().unwrap()
        }
    }

Run
source

#### pub fn new_uninit() -> Rc<MaybeUninit<T>>

🔬This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new `Rc` with uninitialized contents.

##### Examples

    #![feature(new_uninit)]
    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let mut five = Rc::<u32>::new_uninit();

    // Deferred initialization:
    Rc::get_mut(&mut five).unwrap().write(5);

    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5)

Run
source

#### pub fn new_zeroed() -> Rc<MaybeUninit<T>>

🔬This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new `Rc` with uninitialized contents, with the memory being filled with `0` bytes.

See `MaybeUninit::zeroed` for examples of correct and incorrect usage of this method.

##### Examples

    #![feature(new_uninit)]

    use std::rc::Rc;

    let zero = Rc::<u32>::new_zeroed();
    let zero = unsafe { zero.assume_init() };

    assert_eq!(*zero, 0)

Run
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#### pub fn try_new(value: T) -> Result<Rc<T>, AllocError>

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

Constructs a new `Rc<T>`, returning an error if the allocation fails

##### Examples

    #![feature(allocator_api)]
    use std::rc::Rc;

    let five = Rc::try_new(5);

Run
source

#### pub fn try_new_uninit() -> Result<Rc<MaybeUninit<T>>, AllocError>

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

Constructs a new `Rc` with uninitialized contents, returning an error if the allocation fails

##### Examples

    #![feature(allocator_api, new_uninit)]
    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let mut five = Rc::<u32>::try_new_uninit()?;

    // Deferred initialization:
    Rc::get_mut(&mut five).unwrap().write(5);

    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5);

Run
source

#### pub fn try_new_zeroed() -> Result<Rc<MaybeUninit<T>>, AllocError>

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

Constructs a new `Rc` with uninitialized contents, with the memory being filled with `0` bytes, returning an error if the allocation fails

See `MaybeUninit::zeroed` for examples of correct and incorrect usage of this method.

##### Examples

    #![feature(allocator_api, new_uninit)]

    use std::rc::Rc;

    let zero = Rc::<u32>::try_new_zeroed()?;
    let zero = unsafe { zero.assume_init() };

    assert_eq!(*zero, 0);

Run
1.33.0 · source

#### pub fn pin(value: T) -> Pin<Rc<T>>

Constructs a new `Pin<Rc<T>>`. If `T` does not implement `Unpin`, then `value` will be pinned in memory and unable to be moved.

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### impl<T, A: Allocator> Rc<T, A>

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#### pub fn allocator(this: &Self) -> &A

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

Returns a reference to the underlying allocator.

Note: this is an associated function, which means that you have to call it as `Rc::allocator(&r)` instead of `r.allocator()`. This is so that there is no conflict with a method on the inner type.

source

#### pub fn new_in(value: T, alloc: A) -> Rc<T, A>

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

Constructs a new `Rc` in the provided allocator.

##### Examples

    #![feature(allocator_api)]
    use std::rc::Rc;
    use std::alloc::System;

    let five = Rc::new_in(5, System);

Run
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#### pub fn new_uninit_in(alloc: A) -> Rc<MaybeUninit<T>, A>

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

Constructs a new `Rc` with uninitialized contents in the provided allocator.

##### Examples

    #![feature(new_uninit)]
    #![feature(get_mut_unchecked)]
    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let mut five = Rc::<u32, _>::new_uninit_in(System);

    let five = unsafe {
        // Deferred initialization:
        Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);

        five.assume_init()
    };

    assert_eq!(*five, 5)

Run
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#### pub fn new_zeroed_in(alloc: A) -> Rc<MaybeUninit<T>, A>

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

Constructs a new `Rc` with uninitialized contents, with the memory being filled with `0` bytes, in the provided allocator.

See `MaybeUninit::zeroed` for examples of correct and incorrect usage of this method.

##### Examples

    #![feature(new_uninit)]
    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let zero = Rc::<u32, _>::new_zeroed_in(System);
    let zero = unsafe { zero.assume_init() };

    assert_eq!(*zero, 0)

Run
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#### pub fn try_new_in(value: T, alloc: A) -> Result<Self, AllocError>

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

Constructs a new `Rc<T>` in the provided allocator, returning an error if the allocation fails

##### Examples

    #![feature(allocator_api)]
    use std::rc::Rc;
    use std::alloc::System;

    let five = Rc::try_new_in(5, System);

Run
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#### pub fn try_new_uninit_in(alloc: A) -> Result<Rc<MaybeUninit<T>, A>, AllocError>

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

Constructs a new `Rc` with uninitialized contents, in the provided allocator, returning an error if the allocation fails

##### Examples

    #![feature(allocator_api, new_uninit)]
    #![feature(get_mut_unchecked)]

    use std::rc::Rc;
    use std::alloc::System;

    let mut five = Rc::<u32, _>::try_new_uninit_in(System)?;

    let five = unsafe {
        // Deferred initialization:
        Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);

        five.assume_init()
    };

    assert_eq!(*five, 5);

Run
source

#### pub fn try_new_zeroed_in(alloc: A) -> Result<Rc<MaybeUninit<T>, A>, AllocError>

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

Constructs a new `Rc` with uninitialized contents, with the memory being filled with `0` bytes, in the provided allocator, returning an error if the allocation fails

See `MaybeUninit::zeroed` for examples of correct and incorrect usage of this method.

##### Examples

    #![feature(allocator_api, new_uninit)]

    use std::rc::Rc;
    use std::alloc::System;

    let zero = Rc::<u32, _>::try_new_zeroed_in(System)?;
    let zero = unsafe { zero.assume_init() };

    assert_eq!(*zero, 0);

Run
source

#### pub fn pin_in(value: T, alloc: A) -> Pin<Self>

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

Constructs a new `Pin<Rc<T>>` in the provided allocator. If `T` does not implement `Unpin`, then `value` will be pinned in memory and unable to be moved.

1.4.0 · source

#### pub fn try_unwrap(this: Self) -> Result<T, Self>

Returns the inner value, if the `Rc` has exactly one strong reference.

Otherwise, an `Err` is returned with the same `Rc` that was passed in.

This will succeed even if there are outstanding weak references.

##### Examples

    use std::rc::Rc;

    let x = Rc::new(3);
    assert_eq!(Rc::try_unwrap(x), Ok(3));

    let x = Rc::new(4);
    let _y = Rc::clone(&x);
    assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);

Run
1.70.0 · source

#### pub fn into_inner(this: Self) -> Option<T>

Returns the inner value, if the `Rc` has exactly one strong reference.

Otherwise, `None` is returned and the `Rc` is dropped.

This will succeed even if there are outstanding weak references.

If `Rc::into_inner` is called on every clone of this `Rc`, it is guaranteed that exactly one of the calls returns the inner value. This means in particular that the inner value is not dropped.

This is equivalent to `Rc::try_unwrap(this).ok()`. (Note that these are not equivalent for `Arc`, due to race conditions that do not apply to `Rc`.)

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### impl<T> Rc<[T]>

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#### pub fn new_uninit_slice(len: usize) -> Rc<[MaybeUninit<T>]>

🔬This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new reference-counted slice with uninitialized contents.

##### Examples

    #![feature(new_uninit)]
    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let mut values = Rc::<[u32]>::new_uninit_slice(3);

    // Deferred initialization:
    let data = Rc::get_mut(&mut values).unwrap();
    data[0].write(1);
    data[1].write(2);
    data[2].write(3);

    let values = unsafe { values.assume_init() };

    assert_eq!(*values, [1, 2, 3])

Run
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#### pub fn new_zeroed_slice(len: usize) -> Rc<[MaybeUninit<T>]>

🔬This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new reference-counted slice with uninitialized contents, with the memory being filled with `0` bytes.

See `MaybeUninit::zeroed` for examples of correct and incorrect usage of this method.

##### Examples

    #![feature(new_uninit)]

    use std::rc::Rc;

    let values = Rc::<[u32]>::new_zeroed_slice(3);
    let values = unsafe { values.assume_init() };

    assert_eq!(*values, [0, 0, 0])

Run
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### impl<T, A: Allocator> Rc<[T], A>

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#### pub fn new_uninit_slice_in(len: usize, alloc: A) -> Rc<[MaybeUninit<T>], A>

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

Constructs a new reference-counted slice with uninitialized contents.

##### Examples

    #![feature(new_uninit)]
    #![feature(get_mut_unchecked)]
    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let mut values = Rc::<[u32], _>::new_uninit_slice_in(3, System);

    let values = unsafe {
        // Deferred initialization:
        Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1);
        Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2);
        Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3);

        values.assume_init()
    };

    assert_eq!(*values, [1, 2, 3])

Run
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#### pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Rc<[MaybeUninit<T>], A>

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

Constructs a new reference-counted slice with uninitialized contents, with the memory being filled with `0` bytes.

See `MaybeUninit::zeroed` for examples of correct and incorrect usage of this method.

##### Examples

    #![feature(new_uninit)]
    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let values = Rc::<[u32], _>::new_zeroed_slice_in(3, System);
    let values = unsafe { values.assume_init() };

    assert_eq!(*values, [0, 0, 0])

Run
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### impl<T, A: Allocator> Rc<MaybeUninit<T>, A>

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#### pub unsafe fn assume_init(self) -> Rc<T, A>where A: Clone,

🔬This is a nightly-only experimental API. (`new_uninit` #63291)

Converts to `Rc<T>`.

##### Safety

As with `MaybeUninit::assume_init`, it is up to the caller to guarantee that the inner value really is in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.

##### Examples

    #![feature(new_uninit)]
    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let mut five = Rc::<u32>::new_uninit();

    // Deferred initialization:
    Rc::get_mut(&mut five).unwrap().write(5);

    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5)

Run
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### impl<T, A: Allocator> Rc<[MaybeUninit<T>], A>

source

#### pub unsafe fn assume_init(self) -> Rc<[T], A>where A: Clone,

🔬This is a nightly-only experimental API. (`new_uninit` #63291)

Converts to `Rc<[T]>`.

##### Safety

As with `MaybeUninit::assume_init`, it is up to the caller to guarantee that the inner value really is in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.

##### Examples

    #![feature(new_uninit)]
    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let mut values = Rc::<[u32]>::new_uninit_slice(3);

    // Deferred initialization:
    let data = Rc::get_mut(&mut values).unwrap();
    data[0].write(1);
    data[1].write(2);
    data[2].write(3);

    let values = unsafe { values.assume_init() };

    assert_eq!(*values, [1, 2, 3])

Run
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### impl<T: ?Sized> Rc<T>

1.17.0 · source

#### pub unsafe fn from_raw(ptr: *const T) -> Self

Constructs an `Rc<T>` from a raw pointer.

The raw pointer must have been previously returned by a call to `Rc<U>::into_raw` where `U` must have the same size and alignment as `T`. This is trivially true if `U` is `T`. Note that if `U` is not `T` but has the same size and alignment, this is basically like transmuting references of different types. See `mem::transmute` for more information on what restrictions apply in this case.

The raw pointer must point to a block of memory allocated by the global allocator

The user of `from_raw` has to make sure a specific value of `T` is only dropped once.

This function is unsafe because improper use may lead to memory unsafety, even if the returned `Rc<T>` is never accessed.

##### Examples

    use std::rc::Rc;

    let x = Rc::new("hello".to_owned());
    let x_ptr = Rc::into_raw(x);

    unsafe {
        // Convert back to an `Rc` to prevent leak.
        let x = Rc::from_raw(x_ptr);
        assert_eq!(&*x, "hello");

        // Further calls to `Rc::from_raw(x_ptr)` would be memory-unsafe.
    }

    // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!

Run
1.53.0 · source

#### pub unsafe fn increment_strong_count(ptr: *const T)

Increments the strong reference count on the `Rc<T>` associated with the provided pointer by one.

##### Safety

The pointer must have been obtained through `Rc::into_raw`, the associated `Rc` instance must be valid (i.e. the strong count must be at least 1) for the duration of this method, and `ptr` must point to a block of memory allocated by the global allocator.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    unsafe {
        let ptr = Rc::into_raw(five);
        Rc::increment_strong_count(ptr);

        let five = Rc::from_raw(ptr);
        assert_eq!(2, Rc::strong_count(&five));
    }

Run
1.53.0 · source

#### pub unsafe fn decrement_strong_count(ptr: *const T)

Decrements the strong reference count on the `Rc<T>` associated with the provided pointer by one.

##### Safety

The pointer must have been obtained through `Rc::into_raw`, the associated `Rc` instance must be valid (i.e. the strong count must be at least 1) when invoking this method, and `ptr` must point to a block of memory allocated by the global allocator. This method can be used to release the final `Rc` and backing storage, but should not be called after the final `Rc` has been released.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    unsafe {
        let ptr = Rc::into_raw(five);
        Rc::increment_strong_count(ptr);

        let five = Rc::from_raw(ptr);
        assert_eq!(2, Rc::strong_count(&five));
        Rc::decrement_strong_count(ptr);
        assert_eq!(1, Rc::strong_count(&five));
    }

Run
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### impl<T: ?Sized, A: Allocator> Rc<T, A>

1.17.0 · source

#### pub fn into_raw(this: Self) -> *const T

Consumes the `Rc`, returning the wrapped pointer.

To avoid a memory leak the pointer must be converted back to an `Rc` using `Rc::from_raw`.

##### Examples

    use std::rc::Rc;

    let x = Rc::new("hello".to_owned());
    let x_ptr = Rc::into_raw(x);
    assert_eq!(unsafe { &*x_ptr }, "hello");

Run
1.45.0 · source

#### pub fn as_ptr(this: &Self) -> *const T

Provides a raw pointer to the data.

The counts are not affected in any way and the `Rc` is not consumed. The pointer is valid for as long there are strong counts in the `Rc`.

##### Examples

    use std::rc::Rc;

    let x = Rc::new("hello".to_owned());
    let y = Rc::clone(&x);
    let x_ptr = Rc::as_ptr(&x);
    assert_eq!(x_ptr, Rc::as_ptr(&y));
    assert_eq!(unsafe { &*x_ptr }, "hello");

Run
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#### pub unsafe fn from_raw_in(ptr: *const T, alloc: A) -> Self

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

Constructs an `Rc<T, A>` from a raw pointer in the provided allocator.

The raw pointer must have been previously returned by a call to `Rc<U, A>::into_raw` where `U` must have the same size and alignment as `T`. This is trivially true if `U` is `T`. Note that if `U` is not `T` but has the same size and alignment, this is basically like transmuting references of different types. See `mem::transmute` for more information on what restrictions apply in this case.

The raw pointer must point to a block of memory allocated by `alloc`

The user of `from_raw` has to make sure a specific value of `T` is only dropped once.

This function is unsafe because improper use may lead to memory unsafety, even if the returned `Rc<T>` is never accessed.

##### Examples

    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let x = Rc::new_in("hello".to_owned(), System);
    let x_ptr = Rc::into_raw(x);

    unsafe {
        // Convert back to an `Rc` to prevent leak.
        let x = Rc::from_raw_in(x_ptr, System);
        assert_eq!(&*x, "hello");

        // Further calls to `Rc::from_raw(x_ptr)` would be memory-unsafe.
    }

    // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!

Run
1.4.0 · source

#### pub fn downgrade(this: &Self) -> Weak<T, A>where A: Clone,

Creates a new `Weak` pointer to this allocation.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    let weak_five = Rc::downgrade(&five);

Run
1.15.0 · source

#### pub fn weak_count(this: &Self) -> usize

Gets the number of `Weak` pointers to this allocation.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);
    let _weak_five = Rc::downgrade(&five);

    assert_eq!(1, Rc::weak_count(&five));

Run
1.15.0 · source

#### pub fn strong_count(this: &Self) -> usize

Gets the number of strong (`Rc`) pointers to this allocation.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);
    let _also_five = Rc::clone(&five);

    assert_eq!(2, Rc::strong_count(&five));

Run
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#### pub unsafe fn increment_strong_count_in(ptr: *const T, alloc: A)where A: Clone,

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

Increments the strong reference count on the `Rc<T>` associated with the provided pointer by one.

##### Safety

The pointer must have been obtained through `Rc::into_raw`, the associated `Rc` instance must be valid (i.e. the strong count must be at least 1) for the duration of this method, and `ptr` must point to a block of memory allocated by `alloc`

##### Examples

    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let five = Rc::new_in(5, System);

    unsafe {
        let ptr = Rc::into_raw(five);
        Rc::increment_strong_count_in(ptr, System);

        let five = Rc::from_raw_in(ptr, System);
        assert_eq!(2, Rc::strong_count(&five));
    }

Run
source

#### pub unsafe fn decrement_strong_count_in(ptr: *const T, alloc: A)

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

Decrements the strong reference count on the `Rc<T>` associated with the provided pointer by one.

##### Safety

The pointer must have been obtained through `Rc::into_raw`, the associated `Rc` instance must be valid (i.e. the strong count must be at least 1) when invoking this method, and `ptr` must point to a block of memory allocated by `alloc`. This method can be used to release the final `Rc` and backing storage, but should not be called after the final `Rc` has been released.

##### Examples

    #![feature(allocator_api)]

    use std::rc::Rc;
    use std::alloc::System;

    let five = Rc::new_in(5, System);

    unsafe {
        let ptr = Rc::into_raw(five);
        Rc::increment_strong_count_in(ptr, System);

        let five = Rc::from_raw_in(ptr, System);
        assert_eq!(2, Rc::strong_count(&five));
        Rc::decrement_strong_count_in(ptr, System);
        assert_eq!(1, Rc::strong_count(&five));
    }

Run
1.4.0 · source

#### pub fn get_mut(this: &mut Self) -> Option<&mut T>

Returns a mutable reference into the given `Rc`, if there are no other `Rc` or `Weak` pointers to the same allocation.

Returns `None` otherwise, because it is not safe to mutate a shared value.

See also `make_mut`, which will `clone` the inner value when there are other `Rc` pointers.

##### Examples

    use std::rc::Rc;

    let mut x = Rc::new(3);
    *Rc::get_mut(&mut x).unwrap() = 4;
    assert_eq!(*x, 4);

    let _y = Rc::clone(&x);
    assert!(Rc::get_mut(&mut x).is_none());

Run
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#### pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T

🔬This is a nightly-only experimental API. (`get_mut_unchecked` #63292)

Returns a mutable reference into the given `Rc`, without any check.

See also `get_mut`, which is safe and does appropriate checks.

##### Safety

If any other `Rc` or `Weak` pointers to the same allocation exist, then they must not be dereferenced or have active borrows for the duration of the returned borrow, and their inner type must be exactly the same as the inner type of this Rc (including lifetimes). This is trivially the case if no such pointers exist, for example immediately after `Rc::new`.

##### Examples

    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let mut x = Rc::new(String::new());
    unsafe {
        Rc::get_mut_unchecked(&mut x).push_str("foo")
    }
    assert_eq!(*x, "foo");

Run

Other `Rc` pointers to the same allocation must be to the same type.

    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let x: Rc<str> = Rc::from("Hello, world!");
    let mut y: Rc<[u8]> = x.clone().into();
    unsafe {
        // this is Undefined Behavior, because x's inner type is str, not [u8]
        Rc::get_mut_unchecked(&mut y).fill(0xff); // 0xff is invalid in UTF-8
    }
    println!("{}", &*x); // Invalid UTF-8 in a str

Run

Other `Rc` pointers to the same allocation must be to the exact same type, including lifetimes.

    #![feature(get_mut_unchecked)]

    use std::rc::Rc;

    let x: Rc<&str> = Rc::new("Hello, world!");
    {
        let s = String::from("Oh, no!");
        let mut y: Rc<&str> = x.clone().into();
        unsafe {
            // this is Undefined Behavior, because x's inner type
            // is &'long str, not &'short str
            *Rc::get_mut_unchecked(&mut y) = &s;
        }
    }
    println!("{}", &*x); // Use-after-free

Run
1.17.0 · source

#### pub fn ptr_eq(this: &Self, other: &Self) -> bool

Returns `true` if the two `Rc`s point to the same allocation in a vein similar to `ptr::eq`. This function ignores the metadata of `dyn Trait` pointers.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);
    let same_five = Rc::clone(&five);
    let other_five = Rc::new(5);

    assert!(Rc::ptr_eq(&five, &same_five));
    assert!(!Rc::ptr_eq(&five, &other_five));

Run
source§

### impl<T: Clone, A: Allocator + Clone> Rc<T, A>

1.4.0 · source

#### pub fn make_mut(this: &mut Self) -> &mut T

Makes a mutable reference into the given `Rc`.

If there are other `Rc` pointers to the same allocation, then `make_mut` will `clone` the inner value to a new allocation to ensure unique ownership. This is also referred to as clone-on-write.

However, if there are no other `Rc` pointers to this allocation, but some `Weak` pointers, then the `Weak` pointers will be disassociated and the inner value will not be cloned.

See also `get_mut`, which will fail rather than cloning the inner value or disassociating `Weak` pointers.

##### Examples

    use std::rc::Rc;

    let mut data = Rc::new(5);

    *Rc::make_mut(&mut data) += 1;         // Won't clone anything
    let mut other_data = Rc::clone(&data); // Won't clone inner data
    *Rc::make_mut(&mut data) += 1;         // Clones inner data
    *Rc::make_mut(&mut data) += 1;         // Won't clone anything
    *Rc::make_mut(&mut other_data) *= 2;   // Won't clone anything

    // Now `data` and `other_data` point to different allocations.
    assert_eq!(*data, 8);
    assert_eq!(*other_data, 12);

Run

`Weak` pointers will be disassociated:

    use std::rc::Rc;

    let mut data = Rc::new(75);
    let weak = Rc::downgrade(&data);

    assert!(75 == *data);
    assert!(75 == *weak.upgrade().unwrap());

    *Rc::make_mut(&mut data) += 1;

    assert!(76 == *data);
    assert!(weak.upgrade().is_none());

Run
source

#### pub fn unwrap_or_clone(this: Self) -> T

🔬This is a nightly-only experimental API. (`arc_unwrap_or_clone` #93610)

If we have the only reference to `T` then unwrap it. Otherwise, clone `T` and return the clone.

Assuming `rc_t` is of type `Rc<T>`, this function is functionally equivalent to `(*rc_t).clone()`, but will avoid cloning the inner value where possible.

##### Examples

    #![feature(arc_unwrap_or_clone)]
    let inner = String::from("test");
    let ptr = inner.as_ptr();

    let rc = Rc::new(inner);
    let inner = Rc::unwrap_or_clone(rc);
    // The inner value was not cloned
    assert!(ptr::eq(ptr, inner.as_ptr()));

    let rc = Rc::new(inner);
    let rc2 = rc.clone();
    let inner = Rc::unwrap_or_clone(rc);
    // Because there were 2 references, we had to clone the inner value.
    assert!(!ptr::eq(ptr, inner.as_ptr()));
    // `rc2` is the last reference, so when we unwrap it we get back
    // the original `String`.
    let inner = Rc::unwrap_or_clone(rc2);
    assert!(ptr::eq(ptr, inner.as_ptr()));

Run
source§

### impl<A: Allocator + Clone> Rc<dyn Any, A>

1.29.0 · source

#### pub fn downcast<T: Any>(self) -> Result<Rc<T, A>, Self>

Attempt to downcast the `Rc<dyn Any>` to a concrete type.

##### Examples

    use std::any::Any;
    use std::rc::Rc;

    fn print_if_string(value: Rc<dyn Any>) {
        if let Ok(string) = value.downcast::<String>() {
            println!("String ({}): {}", string.len(), string);
        }
    }

    let my_string = "Hello World".to_string();
    print_if_string(Rc::new(my_string));
    print_if_string(Rc::new(0i8));

Run
source

#### pub unsafe fn downcast_unchecked<T: Any>(self) -> Rc<T, A>

🔬This is a nightly-only experimental API. (`downcast_unchecked` #90850)

Downcasts the `Rc<dyn Any>` to a concrete type.

For a safe alternative see `downcast`.

##### Examples

    #![feature(downcast_unchecked)]

    use std::any::Any;
    use std::rc::Rc;

    let x: Rc<dyn Any> = Rc::new(1_usize);

    unsafe {
        assert_eq!(*x.downcast_unchecked::<usize>(), 1);
    }

Run

##### Safety

The contained value must be of type `T`. Calling this method with the incorrect type is undefined behavior.

## Trait Implementations§

1.5.0 · source§

### impl<T: ?Sized, A: Allocator> AsRef<T> for Rc<T, A>

source§

#### fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.
source§

### impl<T: ?Sized, A: Allocator> Borrow<T> for Rc<T, A>

source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

### impl<T: ?Sized, A: Allocator + Clone> Clone for Rc<T, A>

source§

#### fn clone(&self) -> Self

Makes a clone of the `Rc` pointer.

This creates another pointer to the same allocation, increasing the strong reference count.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    let _ = Rc::clone(&five);

Run
source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
source§

### impl<T: ?Sized + Debug, A: Allocator> Debug for Rc<T, A>

source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

### impl<T: Default> Default for Rc<T>

source§

#### fn default() -> Rc<T>

Creates a new `Rc<T>`, with the `Default` value for `T`.

##### Examples

    use std::rc::Rc;

    let x: Rc<i32> = Default::default();
    assert_eq!(*x, 0);

Run
source§

### impl<T: ?Sized, A: Allocator> Deref for Rc<T, A>

§

#### type Target = T

The resulting type after dereferencing.
source§

#### fn deref(&self) -> &T

Dereferences the value.
source§

### impl<T: ?Sized + Display, A: Allocator> Display for Rc<T, A>

source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

### impl<T: ?Sized, A: Allocator> Drop for Rc<T, A>

source§

#### fn drop(&mut self)

Drops the `Rc`.

This will decrement the strong reference count. If the strong reference count reaches zero then the only other references (if any) are `Weak`, so we `drop` the inner value.

##### Examples

    use std::rc::Rc;

    struct Foo;

    impl Drop for Foo {
        fn drop(&mut self) {
            println!("dropped!");
        }
    }

    let foo  = Rc::new(Foo);
    let foo2 = Rc::clone(&foo);

    drop(foo);    // Doesn't print anything
    drop(foo2);   // Prints "dropped!"

Run
1.21.0 · source§

### impl<T: Clone> From<&[T]> for Rc<[T]>

source§

#### fn from(v: &[T]) -> Rc<[T]>

Allocate a reference-counted slice and fill it by cloning `v`’s items.

##### Example

    let original: &[i32] = &[1, 2, 3];
    let shared: Rc<[i32]> = Rc::from(original);
    assert_eq!(&[1, 2, 3], &shared[..]);

Run
1.24.0 · source§

### impl From<&CStr> for Rc<CStr>

source§

#### fn from(s: &CStr) -> Rc<CStr>

Converts a `&CStr` into a `Rc<CStr>`, by copying the contents into a newly allocated `Rc`.

1.21.0 · source§

### impl From<&str> for Rc<str>

source§

#### fn from(v: &str) -> Rc<str>

Allocate a reference-counted string slice and copy `v` into it.

##### Example

    let shared: Rc<str> = Rc::from("statue");
    assert_eq!("statue", &shared[..]);

Run
1.74.0 · source§

### impl<T, const N: usize> From<[T; N]> for Rc<[T]>

source§

#### fn from(v: [T; N]) -> Rc<[T]>

Converts a `[T; N]` into an `Rc<[T]>`.

The conversion moves the array into a newly allocated `Rc`.

##### Example

    let original: [i32; 3] = [1, 2, 3];
    let shared: Rc<[i32]> = Rc::from(original);
    assert_eq!(&[1, 2, 3], &shared[..]);

Run
1.21.0 · source§

### impl<T: ?Sized, A: Allocator> From<Box<T, A>> for Rc<T, A>

source§

#### fn from(v: Box<T, A>) -> Rc<T, A>

Move a boxed object to a new, reference counted, allocation.

##### Example

    let original: Box<i32> = Box::new(1);
    let shared: Rc<i32> = Rc::from(original);
    assert_eq!(1, *shared);

Run
1.24.0 · source§

### impl From<CString> for Rc<CStr>

source§

#### fn from(s: CString) -> Rc<CStr>

Converts a `CString` into an `Rc<CStr>` by moving the `CString` data into a new `Rc` buffer.

1.45.0 · source§

### impl<'a, B> From<Cow<'a, B>> for Rc<B>where B: ToOwned + ?Sized, Rc<B>: From<&'a B> + From<B::Owned>,

source§

#### fn from(cow: Cow<'a, B>) -> Rc<B>

Create a reference-counted pointer from a clone-on-write pointer by copying its content.

##### Example

    let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
    let shared: Rc<str> = Rc::from(cow);
    assert_eq!("eggplant", &shared[..]);

Run
1.62.0 · source§

### impl From<Rc<str>> for Rc<[u8]>

source§

#### fn from(rc: Rc<str>) -> Self

Converts a reference-counted string slice into a byte slice.

##### Example

    let string: Rc<str> = Rc::from("eggplant");
    let bytes: Rc<[u8]> = Rc::from(string);
    assert_eq!("eggplant".as_bytes(), bytes.as_ref());

Run
1.21.0 · source§

### impl From<String> for Rc<str>

source§

#### fn from(v: String) -> Rc<str>

Allocate a reference-counted string slice and copy `v` into it.

##### Example

    let original: String = "statue".to_owned();
    let shared: Rc<str> = Rc::from(original);
    assert_eq!("statue", &shared[..]);

Run
1.6.0 · source§

### impl<T> From<T> for Rc<T>

source§

#### fn from(t: T) -> Self

Converts a generic type `T` into an `Rc<T>`

The conversion allocates on the heap and moves `t` from the stack into it.

##### Example

    let x = 5;
    let rc = Rc::new(5);

    assert_eq!(Rc::from(x), rc);

Run
1.21.0 · source§

### impl<T, A: Allocator> From<Vec<T, A>> for Rc<[T], A>

source§

#### 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
1.37.0 · source§

### impl<T> FromIterator<T> for Rc<[T]>

source§

#### fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self

Takes each element in the `Iterator` and collects it into an `Rc<[T]>`.

##### Performance characteristics

###### The general case

In the general case, collecting into `Rc<[T]>` is done by first collecting into a `Vec<T>`. That is, when writing the following:

    let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();

Run

this behaves as if we wrote:

    let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0)
        .collect::<Vec<_>>() // The first set of allocations happens here.
        .into(); // A second allocation for `Rc<[T]>` happens here.

Run

This will allocate as many times as needed for constructing the `Vec<T>` and then it will allocate once for turning the `Vec<T>` into the `Rc<[T]>`.

###### Iterators of known length

When your `Iterator` implements `TrustedLen` and is of an exact size, a single allocation will be made for the `Rc<[T]>`. For example:

    let evens: Rc<[u8]> = (0..10).collect(); // Just a single allocation happens here.

Run
source§

### impl<T: ?Sized + Hash, A: Allocator> Hash for Rc<T, A>

source§

#### 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
source§

### impl<T: ?Sized + Ord, A: Allocator> Ord for Rc<T, A>

source§

#### fn cmp(&self, other: &Rc<T, A>) -> Ordering

Comparison for two `Rc`s.

The two are compared by calling `cmp()` on their inner values.

##### Examples

    use std::rc::Rc;
    use std::cmp::Ordering;

    let five = Rc::new(5);

    assert_eq!(Ordering::Less, five.cmp(&Rc::new(6)));

Run
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: ?Sized + PartialEq, A: Allocator> PartialEq for Rc<T, A>

source§

#### fn eq(&self, other: &Rc<T, A>) -> bool

Equality for two `Rc`s.

Two `Rc`s are equal if their inner values are equal, even if they are stored in different allocation.

If `T` also implements `Eq` (implying reflexivity of equality), two `Rc`s that point to the same allocation are always equal.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(five == Rc::new(5));

Run
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#### fn ne(&self, other: &Rc<T, A>) -> bool

Inequality for two `Rc`s.

Two `Rc`s are not equal if their inner values are not equal.

If `T` also implements `Eq` (implying reflexivity of equality), two `Rc`s that point to the same allocation are always equal.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(five != Rc::new(6));

Run
source§

### impl<T: ?Sized + PartialOrd, A: Allocator> PartialOrd for Rc<T, A>

source§

#### fn partial_cmp(&self, other: &Rc<T, A>) -> Option<Ordering>

Partial comparison for two `Rc`s.

The two are compared by calling `partial_cmp()` on their inner values.

##### Examples

    use std::rc::Rc;
    use std::cmp::Ordering;

    let five = Rc::new(5);

    assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6)));

Run
source§

#### fn lt(&self, other: &Rc<T, A>) -> bool

Less-than comparison for two `Rc`s.

The two are compared by calling `<` on their inner values.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(five < Rc::new(6));

Run
source§

#### fn le(&self, other: &Rc<T, A>) -> bool

‘Less than or equal to’ comparison for two `Rc`s.

The two are compared by calling `<=` on their inner values.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(five <= Rc::new(5));

Run
source§

#### fn gt(&self, other: &Rc<T, A>) -> bool

Greater-than comparison for two `Rc`s.

The two are compared by calling `>` on their inner values.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(five > Rc::new(4));

Run
source§

#### fn ge(&self, other: &Rc<T, A>) -> bool

‘Greater than or equal to’ comparison for two `Rc`s.

The two are compared by calling `>=` on their inner values.

##### Examples

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(five >= Rc::new(5));

Run
source§

### impl<T: ?Sized, A: Allocator> Pointer for Rc<T, A>

source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.
1.43.0 · source§

### impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]>

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#### type Error = Rc<[T]>

The type returned in the event of a conversion error.
source§

#### fn try_from(boxed_slice: Rc<[T]>) -> Result<Self, Self::Error>

Performs the conversion.
source§

### impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<Rc<U, A>> for Rc<T, A>

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### impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T>

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### impl<T: ?Sized + Eq, A: Allocator> Eq for Rc<T, A>

1.58.0 · source§

### impl<T: RefUnwindSafe + ?Sized, A: Allocator + UnwindSafe> RefUnwindSafe for Rc<T, A>

source§

### impl<T: ?Sized, A: Allocator> !Send for Rc<T, A>

source§

### impl<T: ?Sized, A: Allocator> !Sync for Rc<T, A>

1.33.0 · source§

### impl<T: ?Sized, A: Allocator> Unpin for Rc<T, A>

1.9.0 · source§

### impl<T: RefUnwindSafe + ?Sized, A: Allocator + UnwindSafe> UnwindSafe for Rc<T, A>

## Blanket Implementations§

source§

### impl<T> Any for Twhere T: 'static + ?Sized,

source§

#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
source§

### 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,

source§

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<!> for T

source§

#### fn from(t: !) -> T

Converts to this type from the input type.
source§

### impl<T> From<T> for T

source§

#### fn from(t: T) -> T

Returns the argument unchanged.

source§

### impl<T, U> Into<U> for Twhere U: From<T>,

source§

#### 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.
source§

#### 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> ToString for Twhere T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more
source§

### 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.
source§

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

### 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.
source§

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.