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# core::iter::traits::collect::Extend

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.

## Signature

```rust theme={null}
pub trait Extend
```

## Examples

Basic usage:

```rust theme={null}
let mut arr = array![1, 2];

arr.extend(array![3, 4, 5]);

assert_eq!(arr, array![1, 2, 3, 4, 5]);
```

## Trait functions

### extend

Extends a collection with the contents of an iterator.

#### Signature

```rust theme={null}
fn extend,
    +TypeEqual,
    +Destruct,
    +Destruct,
>(
    ref self: T, iter: I,
)
```