Trait Extend 

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

    // Provided methods
    fn extend_one(&mut self, item: A) { ... }
    fn extend_reserve(&mut self, additional: usize) { ... }
    #[doc(hidden)]
    unsafe fn extend_one_unchecked(&mut self, item: A)
       where Self: Sized { ... }
}

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]);

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:?}"));

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 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);

Provided Methods

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

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.

#[doc(hidden)]

unsafe fn extend_one_unchecked(&mut self, item: A)

where Self: Sized,

🔬This is a nightly-only experimental API. (extend_one_unchecked)

Extends a collection with one element, without checking there is enough capacity for it.

Safety

For callers: This must only be called when we know the collection has enough capacity to contain the new item, for example because we previously called extend_reserve.

For implementors: For a collection to unsafely rely on this method’s safety precondition (that is, invoke UB if they are violated), it must implement extend_reserve correctly. In other words, callers may assume that if they extend_reserveed enough space they can call this method.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl Extend<()> for ()

impl<A, B, C, D, E, ExA, ExB, ExC, ExD, ExE> Extend<(A, B, C, D, E)> for (ExA, ExB, ExC, ExD, ExE)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>,

impl<A, B, C, D, E, F, ExA, ExB, ExC, ExD, ExE, ExF> Extend<(A, B, C, D, E, F)> for (ExA, ExB, ExC, ExD, ExE, ExF)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>,

impl<A, B, C, D, E, F, G, ExA, ExB, ExC, ExD, ExE, ExF, ExG> Extend<(A, B, C, D, E, F, G)> for (ExA, ExB, ExC, ExD, ExE, ExF, ExG)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>, ExG: Extend<G>,

impl<A, B, C, D, E, F, G, H, ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH> Extend<(A, B, C, D, E, F, G, H)> for (ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>, ExG: Extend<G>, ExH: Extend<H>,

impl<A, B, C, D, E, F, G, H, I, ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI> Extend<(A, B, C, D, E, F, G, H, I)> for (ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>, ExG: Extend<G>, ExH: Extend<H>, ExI: Extend<I>,

impl<A, B, C, D, E, F, G, H, I, J, ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI, ExJ> Extend<(A, B, C, D, E, F, G, H, I, J)> for (ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI, ExJ)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>, ExG: Extend<G>, ExH: Extend<H>, ExI: Extend<I>, ExJ: Extend<J>,

impl<A, B, C, D, E, F, G, H, I, J, K, ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI, ExJ, ExK> Extend<(A, B, C, D, E, F, G, H, I, J, K)> for (ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI, ExJ, ExK)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>, ExG: Extend<G>, ExH: Extend<H>, ExI: Extend<I>, ExJ: Extend<J>, ExK: Extend<K>,

impl<A, B, C, D, E, F, G, H, I, J, K, L, ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI, ExJ, ExK, ExL> Extend<(A, B, C, D, E, F, G, H, I, J, K, L)> for (ExA, ExB, ExC, ExD, ExE, ExF, ExG, ExH, ExI, ExJ, ExK, ExL)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>, ExE: Extend<E>, ExF: Extend<F>, ExG: Extend<G>, ExH: Extend<H>, ExI: Extend<I>, ExJ: Extend<J>, ExK: Extend<K>, ExL: Extend<L>,

impl<A, B, C, D, ExA, ExB, ExC, ExD> Extend<(A, B, C, D)> for (ExA, ExB, ExC, ExD)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>, ExD: Extend<D>,

impl<A, B, C, ExA, ExB, ExC> Extend<(A, B, C)> for (ExA, ExB, ExC)

where ExA: Extend<A>, ExB: Extend<B>, ExC: Extend<C>,

impl<A, B, ExA, ExB> Extend<(A, B)> for (ExA, ExB)

where ExA: Extend<A>, ExB: Extend<B>,

impl<T, ExtendT> Extend<(T₁, T₂, …, Tₙ)> for (ExtendT₁, ExtendT₂, …, ExtendTₙ)

where ExtendT: Extend<T>,

This trait is implemented for tuples up to twelve items long. The impls for 1- and 3- through 12-ary tuples were stabilized after 2-tuples, in 1.85.0.