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) { ... }
}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]);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§
sourcefn extend<T: IntoIterator<Item = A>>(&mut self, iter: T)
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
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);Provided Methods§
sourcefn extend_one(&mut self, item: A)
fn extend_one(&mut self, item: A)
extend_one #72631)Extends a collection with exactly one element.
sourcefn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one #72631)Reserves capacity in a collection for the given number of additional elements.
The default implementation does nothing.