# 1.0.0[−][src]Trait core::iter::Extend

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

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

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

Extends a collection with the contents of an iterator.

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

# Examples

Basic usage:

    // 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

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## Implementors

### `impl Extend<()> for ()`[src]

#### `fn extend<T: IntoIterator<Item = ()>>(&mut self, iter: T)`[src]

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