# Trait std::iter::Extend

1.0.0 · source ·

    pub trait Extend<A> {
        // Required method
        fn extend<T>(&mut self, iter: T)
           where T: IntoIterator<Item = A>;

        // Provided methods
        fn extend_one(&mut self, item: A) { ... }
        fn extend_reserve(&mut self, additional: usize) { ... }
    }

Expand description

Extend a collection with the contents of an iterator.

Iterators produce a series of values, and collections can also be thought of as a series of values. The `Extend` trait bridges this gap, allowing you to extend a collection by including the contents of that iterator. When extending a collection with an already existing key, that entry is updated or, in the case of collections that permit multiple entries with equal keys, that entry is inserted.

## Examples

Basic usage:

    // You can extend a String with some chars:
    let mut message = String::from("The first three letters are: ");

    message.extend(&['a', 'b', 'c']);

    assert_eq!("abc", &message[29..32]);

Run

Implementing `Extend`:

    // A sample collection, that's just a wrapper over Vec<T>
    #[derive(Debug)]
    struct MyCollection(Vec<i32>);

    // Let's give it some methods so we can create one and add things
    // to it.
    impl MyCollection {
        fn new() -> MyCollection {
            MyCollection(Vec::new())
        }

        fn add(&mut self, elem: i32) {
            self.0.push(elem);
        }
    }

    // since MyCollection has a list of i32s, we implement Extend for i32
    impl Extend<i32> for MyCollection {

        // This is a bit simpler with the concrete type signature: we can call
        // extend on anything which can be turned into an Iterator which gives
        // us i32s. Because we need i32s to put into MyCollection.
        fn extend<T: IntoIterator<Item=i32>>(&mut self, iter: T) {

            // The implementation is very straightforward: loop through the
            // iterator, and add() each element to ourselves.
            for elem in iter {
                self.add(elem);
            }
        }
    }

    let mut c = MyCollection::new();

    c.add(5);
    c.add(6);
    c.add(7);

    // let's extend our collection with three more numbers
    c.extend(vec![1, 2, 3]);

    // we've added these elements onto the end
    assert_eq!("MyCollection([5, 6, 7, 1, 2, 3])", format!("{c:?}"));

Run

## Required Methods§

source

#### fn extend<T>(&mut self, iter: T)where T: IntoIterator<Item = A>,

Extends a collection with the contents of an iterator.

As this is the only required method for this trait, the trait-level docs contain more details.

##### Examples

    // You can extend a String with some chars:
    let mut message = String::from("abc");

    message.extend(['d', 'e', 'f'].iter());

    assert_eq!("abcdef", &message);

Run

## Provided Methods§

source

#### fn extend_one(&mut self, item: A)

🔬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.

The default implementation does nothing.

## Object Safety§

This trait is not object safe.

## Implementors§

source§

### impl Extend<char> for String

1.28.0 · source§

### impl Extend<()> for ()

1.45.0 · source§

### impl Extend<Box<str>> for String

1.52.0 · source§

### impl Extend<OsString> for OsString

1.4.0 · source§

### impl Extend<String> for String

1.2.0 · source§

### impl<'a> Extend<&'a char> for String

source§

### impl<'a> Extend<&'a str> for String

1.52.0 · source§

### impl<'a> Extend<&'a OsStr> for OsString

1.19.0 · source§

### impl<'a> Extend<Cow<'a, str>> for String

1.52.0 · source§

### impl<'a> Extend<Cow<'a, OsStr>> for OsString

1.2.0 · source§

### impl<'a, K, V, A> Extend<(&'a K, &'a V)> for BTreeMap<K, V, A>where K: Ord + Copy, V: Copy, A: Allocator + Clone,

1.4.0 · source§

### impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>where K: Eq + Hash + Copy, V: Copy, S: BuildHasher,

1.2.0 · source§

### impl<'a, T, A> Extend<&'a T> for Vec<T, A>where T: Copy + 'a, A: Allocator,

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.

1.2.0 · source§

### impl<'a, T, A> Extend<&'a T> for BTreeSet<T, A>where T: 'a + Ord + Copy, A: Allocator + Clone,

1.2.0 · source§

### impl<'a, T, A> Extend<&'a T> for BinaryHeap<T, A>where T: 'a + Ord + Copy, A: Allocator,

1.2.0 · source§

### impl<'a, T, A> Extend<&'a T> for LinkedList<T, A>where T: 'a + Copy, A: Allocator,

1.2.0 · source§

### impl<'a, T, A> Extend<&'a T> for VecDeque<T, A>where T: 'a + Copy, A: Allocator,

1.4.0 · source§

### impl<'a, T, S> Extend<&'a T> for HashSet<T, S>where T: 'a + Eq + Hash + Copy, S: BuildHasher,

1.56.0 · source§

### impl<A, B, ExtendA, ExtendB> Extend<(A, B)> for (ExtendA, ExtendB)where ExtendA: Extend<A>, ExtendB: Extend<B>,

source§

### impl<K, V, A> Extend<(K, V)> for BTreeMap<K, V, A>where K: Ord, A: Allocator + Clone,

source§

### impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>where K: Eq + Hash, S: BuildHasher,

Inserts all new key-values from the iterator and replaces values with existing keys with new values returned from the iterator.

source§

### impl<P: AsRef<Path>> Extend<P> for PathBuf

source§

### impl<T, A> Extend<T> for Vec<T, A>where A: Allocator,

source§

### impl<T, A> Extend<T> for BTreeSet<T, A>where T: Ord, A: Allocator + Clone,

source§

### impl<T, A> Extend<T> for BinaryHeap<T, A>where T: Ord, A: Allocator,

source§

### impl<T, A> Extend<T> for LinkedList<T, A>where A: Allocator,

source§

### impl<T, A> Extend<T> for VecDeque<T, A>where A: Allocator,

source§

### impl<T, S> Extend<T> for HashSet<T, S>where T: Eq + Hash, S: BuildHasher,