std::iter::Iterator - Rust
Description: API documentation for the Rust `Iterator` trait in crate `std`.
Keywords: rust, rustlang, rust-lang, Iterator

# Trait std::iter::Iterator 1.0.0 [−] [src]

    pub trait Iterator {
        type Item;
        fn next(&mut self) -> Option<Self::Item>;

        fn size_hint(&self) -> (usize, Option<usize>) { ... }
        fn count(self) -> usize { ... }
        fn last(self) -> Option<Self::Item> { ... }
        fn nth(&mut self, n: usize) -> Option<Self::Item> { ... }
        fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where U: IntoIterator<Item=Self::Item> { ... }
        fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where U: IntoIterator { ... }
        fn map<B, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> B { ... }
        fn filter<P>(self, predicate: P) -> Filter<Self, P> where P: FnMut(&Self::Item) -> bool { ... }
        fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where F: FnMut(Self::Item) -> Option<B> { ... }
        fn enumerate(self) -> Enumerate<Self> { ... }
        fn peekable(self) -> Peekable<Self> { ... }
        fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where P: FnMut(&Self::Item) -> bool { ... }
        fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where P: FnMut(&Self::Item) -> bool { ... }
        fn skip(self, n: usize) -> Skip<Self> { ... }
        fn take(self, n: usize) -> Take<Self> { ... }
        fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where F: FnMut(&mut St, Self::Item) -> Option<B> { ... }
        fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where F: FnMut(Self::Item) -> U, U: IntoIterator { ... }
        fn fuse(self) -> Fuse<Self> { ... }
        fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item) -> () { ... }
        fn by_ref(&mut self) -> &mut Self { ... }
        fn collect<B>(self) -> B where B: FromIterator<Self::Item> { ... }
        fn partition<B, F>(self, f: F) -> (B, B) where B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool { ... }
        fn fold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B { ... }
        fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool { ... }
        fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool { ... }
        fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool { ... }
        fn position<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool { ... }
        fn rposition<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool, Self: ExactSizeIterator + DoubleEndedIterator { ... }
        fn max(self) -> Option<Self::Item> where Self::Item: Ord { ... }
        fn min(self) -> Option<Self::Item> where Self::Item: Ord { ... }
        fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B { ... }
        fn max_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
        fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B { ... }
        fn min_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
        fn rev(self) -> Rev<Self> where Self: DoubleEndedIterator { ... }
        fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Iterator<Item=(A, B)> { ... }
        fn cloned<'a, T>(self) -> Cloned<Self> where Self: Iterator<Item=&'a T>, T: 'a + Clone { ... }
        fn cycle(self) -> Cycle<Self> where Self: Clone { ... }
        fn sum<S>(self) -> S where S: Sum<Self::Item> { ... }
        fn product<P>(self) -> P where P: Product<Self::Item> { ... }
        fn cmp<I>(self, other: I) -> Ordering where I: IntoIterator<Item=Self::Item>, Self::Item: Ord { ... }
        fn partial_cmp<I>(self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
        fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item> { ... }
        fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item> { ... }
        fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
        fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
        fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
        fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
    }

An interface for dealing with iterators.

This is the main iterator trait. For more about the concept of iterators generally, please see the module-level documentation. In particular, you may want to know how to implement `Iterator`.

## Associated Types

### `type Item`

The type of the elements being iterated over.

## Required Methods

### `fn next(&mut self) -> Option<Self::Item>`

Advances the iterator and returns the next value.

Returns `None` when iteration is finished. Individual iterator implementations may choose to resume iteration, and so calling `next()` again may or may not eventually start returning `Some(Item)` again at some point.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    // A call to next() returns the next value...
    assert_eq!(Some(&1), iter.next());
    assert_eq!(Some(&2), iter.next());
    assert_eq!(Some(&3), iter.next());

    // ... and then None once it's over.
    assert_eq!(None, iter.next());

    // More calls may or may not return None. Here, they always will.
    assert_eq!(None, iter.next());
    assert_eq!(None, iter.next());Run

## Provided Methods

### `fn size_hint(&self) -> (usize, Option<usize>)`

Returns the bounds on the remaining length of the iterator.

Specifically, `size_hint()` returns a tuple where the first element is the lower bound, and the second element is the upper bound.

The second half of the tuple that is returned is an `Option<usize>`. A `None` here means that either there is no known upper bound, or the upper bound is larger than `usize`.

# Implementation notes

It is not enforced that an iterator implementation yields the declared number of elements. A buggy iterator may yield less than the lower bound or more than the upper bound of elements.

`size_hint()` is primarily intended to be used for optimizations such as reserving space for the elements of the iterator, but must not be trusted to e.g. omit bounds checks in unsafe code. An incorrect implementation of `size_hint()` should not lead to memory safety violations.

That said, the implementation should provide a correct estimation, because otherwise it would be a violation of the trait's protocol.

The default implementation returns `(0, None)` which is correct for any iterator.

# Examples

Basic usage:

    let a = [1, 2, 3];
    let iter = a.iter();

    assert_eq!((3, Some(3)), iter.size_hint());Run

A more complex example:

    // The even numbers from zero to ten.
    let iter = (0..10).filter(|x| x % 2 == 0);

    // We might iterate from zero to ten times. Knowing that it's five
    // exactly wouldn't be possible without executing filter().
    assert_eq!((0, Some(10)), iter.size_hint());

    // Let's add one five more numbers with chain()
    let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20);

    // now both bounds are increased by five
    assert_eq!((5, Some(15)), iter.size_hint());Run

Returning `None` for an upper bound:

    // an infinite iterator has no upper bound
    let iter = 0..;

    assert_eq!((0, None), iter.size_hint());Run

### `fn count(self) -> usize`

Consumes the iterator, counting the number of iterations and returning it.

This method will evaluate the iterator until its `next()` returns `None`. Once `None` is encountered, `count()` returns the number of times it called `next()`.

# Overflow Behavior

The method does no guarding against overflows, so counting elements of an iterator with more than `usize::MAX` elements either produces the wrong result or panics. If debug assertions are enabled, a panic is guaranteed.

# Panics

This function might panic if the iterator has more than `usize::MAX` elements.

# Examples

Basic usage:

    let a = [1, 2, 3];
    assert_eq!(a.iter().count(), 3);

    let a = [1, 2, 3, 4, 5];
    assert_eq!(a.iter().count(), 5);Run

### `fn last(self) -> Option<Self::Item>`

Consumes the iterator, returning the last element.

This method will evaluate the iterator until it returns `None`. While doing so, it keeps track of the current element. After `None` is returned, `last()` will then return the last element it saw.

# Examples

Basic usage:

    let a = [1, 2, 3];
    assert_eq!(a.iter().last(), Some(&3));

    let a = [1, 2, 3, 4, 5];
    assert_eq!(a.iter().last(), Some(&5));Run

### `fn nth(&mut self, n: usize) -> Option<Self::Item>`

Returns the `n`th element of the iterator.

Note that all preceding elements will be consumed (i.e. discarded).

Like most indexing operations, the count starts from zero, so `nth(0)` returns the first value, `nth(1)` the second, and so on.

`nth()` will return `None` if `n` is greater than or equal to the length of the iterator.

# Examples

Basic usage:

    let a = [1, 2, 3];
    assert_eq!(a.iter().nth(1), Some(&2));Run

Calling `nth()` multiple times doesn't rewind the iterator:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    assert_eq!(iter.nth(1), Some(&2));
    assert_eq!(iter.nth(1), None);Run

Returning `None` if there are less than `n + 1` elements:

    let a = [1, 2, 3];
    assert_eq!(a.iter().nth(10), None);Run

### `fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where U: IntoIterator<Item=Self::Item>`

Takes two iterators and creates a new iterator over both in sequence.

`chain()` will return a new iterator which will first iterate over values from the first iterator and then over values from the second iterator.

In other words, it links two iterators together, in a chain. 🔗

# Examples

Basic usage:

    let a1 = [1, 2, 3];
    let a2 = [4, 5, 6];

    let mut iter = a1.iter().chain(a2.iter());

    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), Some(&3));
    assert_eq!(iter.next(), Some(&4));
    assert_eq!(iter.next(), Some(&5));
    assert_eq!(iter.next(), Some(&6));
    assert_eq!(iter.next(), None);Run

Since the argument to `chain()` uses `IntoIterator`, we can pass anything that can be converted into an `Iterator`, not just an `Iterator` itself. For example, slices (`&[T]`) implement `IntoIterator`, and so can be passed to `chain()` directly:

    let s1 = &[1, 2, 3];
    let s2 = &[4, 5, 6];

    let mut iter = s1.iter().chain(s2);

    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), Some(&3));
    assert_eq!(iter.next(), Some(&4));
    assert_eq!(iter.next(), Some(&5));
    assert_eq!(iter.next(), Some(&6));
    assert_eq!(iter.next(), None);Run

### `fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where U: IntoIterator`

'Zips up' two iterators into a single iterator of pairs.

`zip()` returns a new iterator that will iterate over two other iterators, returning a tuple where the first element comes from the first iterator, and the second element comes from the second iterator.

In other words, it zips two iterators together, into a single one.

When either iterator returns `None`, all further calls to `next()` will return `None`.

# Examples

Basic usage:

    let a1 = [1, 2, 3];
    let a2 = [4, 5, 6];

    let mut iter = a1.iter().zip(a2.iter());

    assert_eq!(iter.next(), Some((&1, &4)));
    assert_eq!(iter.next(), Some((&2, &5)));
    assert_eq!(iter.next(), Some((&3, &6)));
    assert_eq!(iter.next(), None);Run

Since the argument to `zip()` uses `IntoIterator`, we can pass anything that can be converted into an `Iterator`, not just an `Iterator` itself. For example, slices (`&[T]`) implement `IntoIterator`, and so can be passed to `zip()` directly:

    let s1 = &[1, 2, 3];
    let s2 = &[4, 5, 6];

    let mut iter = s1.iter().zip(s2);

    assert_eq!(iter.next(), Some((&1, &4)));
    assert_eq!(iter.next(), Some((&2, &5)));
    assert_eq!(iter.next(), Some((&3, &6)));
    assert_eq!(iter.next(), None);Run

`zip()` is often used to zip an infinite iterator to a finite one. This works because the finite iterator will eventually return `None`, ending the zipper. Zipping with `(0..)` can look a lot like `enumerate()`:

    let enumerate: Vec<_> = "foo".chars().enumerate().collect();

    let zipper: Vec<_> = (0..).zip("foo".chars()).collect();

    assert_eq!((0, 'f'), enumerate[0]);
    assert_eq!((0, 'f'), zipper[0]);

    assert_eq!((1, 'o'), enumerate[1]);
    assert_eq!((1, 'o'), zipper[1]);

    assert_eq!((2, 'o'), enumerate[2]);
    assert_eq!((2, 'o'), zipper[2]);Run

### `fn map<B, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> B`

Takes a closure and creates an iterator which calls that closure on each element.

`map()` transforms one iterator into another, by means of its argument: something that implements `FnMut`. It produces a new iterator which calls this closure on each element of the original iterator.

If you are good at thinking in types, you can think of `map()` like this: If you have an iterator that gives you elements of some type `A`, and you want an iterator of some other type `B`, you can use `map()`, passing a closure that takes an `A` and returns a `B`.

`map()` is conceptually similar to a `for` loop. However, as `map()` is lazy, it is best used when you're already working with other iterators. If you're doing some sort of looping for a side effect, it's considered more idiomatic to use `for` than `map()`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.into_iter().map(|x| 2 * x);

    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), Some(6));
    assert_eq!(iter.next(), None);Run

If you're doing some sort of side effect, prefer `for` to `map()`:

    // don't do this:
    (0..5).map(|x| println!("{}", x));

    // it won't even execute, as it is lazy. Rust will warn you about this.

    // Instead, use for:
    for x in 0..5 {
        println!("{}", x);
    }Run

### `fn filter<P>(self, predicate: P) -> Filter<Self, P> where P: FnMut(&Self::Item) -> bool`

Creates an iterator which uses a closure to determine if an element should be yielded.

The closure must return `true` or `false`. `filter()` creates an iterator which calls this closure on each element. If the closure returns `true`, then the element is returned. If the closure returns `false`, it will try again, and call the closure on the next element, seeing if it passes the test.

# Examples

Basic usage:

    let a = [0i32, 1, 2];

    let mut iter = a.into_iter().filter(|x| x.is_positive());

    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);Run

Because the closure passed to `filter()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation, where the type of the closure is a double reference:

    let a = [0, 1, 2];

    let mut iter = a.into_iter().filter(|x| **x > 1); // need two *s!

    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);Run

It's common to instead use destructuring on the argument to strip away one:

    let a = [0, 1, 2];

    let mut iter = a.into_iter().filter(|&x| *x > 1); // both & and *

    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);Run

or both:

    let a = [0, 1, 2];

    let mut iter = a.into_iter().filter(|&&x| x > 1); // two &s

    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);Run

of these layers.

### `fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where F: FnMut(Self::Item) -> Option<B>`

Creates an iterator that both filters and maps.

The closure must return an `Option<T>`. `filter_map()` creates an iterator which calls this closure on each element. If the closure returns `Some(element)`, then that element is returned. If the closure returns `None`, it will try again, and call the closure on the next element, seeing if it will return `Some`.

Why `filter_map()` and not just `filter()`.`map()`? The key is in this part:

> If the closure returns `Some(element)`, then that element is returned.

In other words, it removes the `Option<T>` layer automatically. If your mapping is already returning an `Option<T>` and you want to skip over `None`s, then `filter_map()` is much, much nicer to use.

# Examples

Basic usage:

    let a = ["1", "2", "lol"];

    let mut iter = a.iter().filter_map(|s| s.parse().ok());

    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);Run

Here's the same example, but with `filter()` and `map()`:

    let a = ["1", "2", "lol"];

    let mut iter = a.iter()
                    .map(|s| s.parse().ok())
                    .filter(|s| s.is_some());

    assert_eq!(iter.next(), Some(Some(1)));
    assert_eq!(iter.next(), Some(Some(2)));
    assert_eq!(iter.next(), None);Run

There's an extra layer of `Some` in there.

### `fn enumerate(self) -> Enumerate<Self>`

Creates an iterator which gives the current iteration count as well as the next value.

The iterator returned yields pairs `(i, val)`, where `i` is the current index of iteration and `val` is the value returned by the iterator.

`enumerate()` keeps its count as a `usize`. If you want to count by a different sized integer, the `zip()` function provides similar functionality.

# Overflow Behavior

The method does no guarding against overflows, so enumerating more than `usize::MAX` elements either produces the wrong result or panics. If debug assertions are enabled, a panic is guaranteed.

# Panics

The returned iterator might panic if the to-be-returned index would overflow a `usize`.

# Examples

    let a = ['a', 'b', 'c'];

    let mut iter = a.iter().enumerate();

    assert_eq!(iter.next(), Some((0, &'a')));
    assert_eq!(iter.next(), Some((1, &'b')));
    assert_eq!(iter.next(), Some((2, &'c')));
    assert_eq!(iter.next(), None);Run

### `fn peekable(self) -> Peekable<Self>`

Creates an iterator which can use `peek` to look at the next element of the iterator without consuming it.

Adds a `peek()` method to an iterator. See its documentation for more information.

Note that the underlying iterator is still advanced when `peek` is called for the first time: In order to retrieve the next element, `next` is called on the underlying iterator, hence any side effects of the `next` method will occur.

# Examples

Basic usage:

    let xs = [1, 2, 3];

    let mut iter = xs.iter().peekable();

    // peek() lets us see into the future
    assert_eq!(iter.peek(), Some(&&1));
    assert_eq!(iter.next(), Some(&1));

    assert_eq!(iter.next(), Some(&2));

    // we can peek() multiple times, the iterator won't advance
    assert_eq!(iter.peek(), Some(&&3));
    assert_eq!(iter.peek(), Some(&&3));

    assert_eq!(iter.next(), Some(&3));

    // after the iterator is finished, so is peek()
    assert_eq!(iter.peek(), None);
    assert_eq!(iter.next(), None);Run

### `fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where P: FnMut(&Self::Item) -> bool`

Creates an iterator that `skip()`s elements based on a predicate.

`skip_while()` takes a closure as an argument. It will call this closure on each element of the iterator, and ignore elements until it returns `false`.

After `false` is returned, `skip_while()`'s job is over, and the rest of the elements are yielded.

# Examples

Basic usage:

    let a = [-1i32, 0, 1];

    let mut iter = a.into_iter().skip_while(|x| x.is_negative());

    assert_eq!(iter.next(), Some(&0));
    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), None);Run

Because the closure passed to `skip_while()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation, where the type of the closure is a double reference:

    let a = [-1, 0, 1];

    let mut iter = a.into_iter().skip_while(|x| **x < 0); // need two *s!

    assert_eq!(iter.next(), Some(&0));
    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), None);Run

Stopping after an initial `false`:

    let a = [-1, 0, 1, -2];

    let mut iter = a.into_iter().skip_while(|x| **x < 0);

    assert_eq!(iter.next(), Some(&0));
    assert_eq!(iter.next(), Some(&1));

    // while this would have been false, since we already got a false,
    // skip_while() isn't used any more
    assert_eq!(iter.next(), Some(&-2));

    assert_eq!(iter.next(), None);Run

### `fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where P: FnMut(&Self::Item) -> bool`

Creates an iterator that yields elements based on a predicate.

`take_while()` takes a closure as an argument. It will call this closure on each element of the iterator, and yield elements while it returns `true`.

After `false` is returned, `take_while()`'s job is over, and the rest of the elements are ignored.

# Examples

Basic usage:

    let a = [-1i32, 0, 1];

    let mut iter = a.into_iter().take_while(|x| x.is_negative());

    assert_eq!(iter.next(), Some(&-1));
    assert_eq!(iter.next(), None);Run

Because the closure passed to `take_while()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation, where the type of the closure is a double reference:

    let a = [-1, 0, 1];

    let mut iter = a.into_iter().take_while(|x| **x < 0); // need two *s!

    assert_eq!(iter.next(), Some(&-1));
    assert_eq!(iter.next(), None);Run

Stopping after an initial `false`:

    let a = [-1, 0, 1, -2];

    let mut iter = a.into_iter().take_while(|x| **x < 0);

    assert_eq!(iter.next(), Some(&-1));

    // We have more elements that are less than zero, but since we already
    // got a false, take_while() isn't used any more
    assert_eq!(iter.next(), None);Run

Because `take_while()` needs to look at the value in order to see if it should be included or not, consuming iterators will see that it is removed:

    let a = [1, 2, 3, 4];
    let mut iter = a.into_iter();

    let result: Vec<i32> = iter.by_ref()
                               .take_while(|n| **n != 3)
                               .cloned()
                               .collect();

    assert_eq!(result, &[1, 2]);

    let result: Vec<i32> = iter.cloned().collect();

    assert_eq!(result, &[4]);Run

The `3` is no longer there, because it was consumed in order to see if the iteration should stop, but wasn't placed back into the iterator or some similar thing.

### `fn skip(self, n: usize) -> Skip<Self>`

Creates an iterator that skips the first `n` elements.

After they have been consumed, the rest of the elements are yielded.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.iter().skip(2);

    assert_eq!(iter.next(), Some(&3));
    assert_eq!(iter.next(), None);Run

### `fn take(self, n: usize) -> Take<Self>`

Creates an iterator that yields its first `n` elements.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.iter().take(2);

    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);Run

`take()` is often used with an infinite iterator, to make it finite:

    let mut iter = (0..).take(3);

    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);Run

### `fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where F: FnMut(&mut St, Self::Item) -> Option<B>`

An iterator adaptor similar to `fold()` that holds internal state and produces a new iterator.

`scan()` takes two arguments: an initial value which seeds the internal state, and a closure with two arguments, the first being a mutable reference to the internal state and the second an iterator element. The closure can assign to the internal state to share state between iterations.

On iteration, the closure will be applied to each element of the iterator and the return value from the closure, an `Option`, is yielded by the iterator.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.iter().scan(1, |state, &x| {
        // each iteration, we'll multiply the state by the element
        *state = *state * x;

        // the value passed on to the next iteration
        Some(*state)
    });

    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(6));
    assert_eq!(iter.next(), None);Run

### `fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where F: FnMut(Self::Item) -> U, U: IntoIterator`

Creates an iterator that works like map, but flattens nested structure.

The `map()` adapter is very useful, but only when the closure argument produces values. If it produces an iterator instead, there's an extra layer of indirection. `flat_map()` will remove this extra layer on its own.

Another way of thinking about `flat_map()`: `map()`'s closure returns one item for each element, and `flat_map()`'s closure returns an iterator for each element.

# Examples

Basic usage:

    let words = ["alpha", "beta", "gamma"];

    // chars() returns an iterator
    let merged: String = words.iter()
                              .flat_map(|s| s.chars())
                              .collect();
    assert_eq!(merged, "alphabetagamma");Run

### `fn fuse(self) -> Fuse<Self>`

Creates an iterator which ends after the first `None`.

After an iterator returns `None`, future calls may or may not yield `Some(T)` again. `fuse()` adapts an iterator, ensuring that after a `None` is given, it will always return `None` forever.

# Examples

Basic usage:

    // an iterator which alternates between Some and None
    struct Alternate {
        state: i32,
    }

    impl Iterator for Alternate {
        type Item = i32;

        fn next(&mut self) -> Option<i32> {
            let val = self.state;
            self.state = self.state + 1;

            // if it's even, Some(i32), else None
            if val % 2 == 0 {
                Some(val)
            } else {
                None
            }
        }
    }

    let mut iter = Alternate { state: 0 };

    // we can see our iterator going back and forth
    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);

    // however, once we fuse it...
    let mut iter = iter.fuse();

    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), None);

    // it will always return None after the first time.
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), None);Run

### `fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item) -> ()`

Do something with each element of an iterator, passing the value on.

When using iterators, you'll often chain several of them together. While working on such code, you might want to check out what's happening at various parts in the pipeline. To do that, insert a call to `inspect()`.

It's much more common for `inspect()` to be used as a debugging tool than to exist in your final code, but never say never.

# Examples

Basic usage:

    let a = [1, 4, 2, 3];

    // this iterator sequence is complex.
    let sum = a.iter()
                .cloned()
                .filter(|&x| x % 2 == 0)
                .fold(0, |sum, i| sum + i);

    println!("{}", sum);

    // let's add some inspect() calls to investigate what's happening
    let sum = a.iter()
                .cloned()
                .inspect(|x| println!("about to filter: {}", x))
                .filter(|&x| x % 2 == 0)
                .inspect(|x| println!("made it through filter: {}", x))
                .fold(0, |sum, i| sum + i);

    println!("{}", sum);Run

This will print:

    about to filter: 1
    about to filter: 4
    made it through filter: 4
    about to filter: 2
    made it through filter: 2
    about to filter: 3
    6

### `fn by_ref(&mut self) -> &mut Self`

Borrows an iterator, rather than consuming it.

This is useful to allow applying iterator adaptors while still retaining ownership of the original iterator.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let iter = a.into_iter();

    let sum: i32 = iter.take(5)
                       .fold(0, |acc, &i| acc + i );

    assert_eq!(sum, 6);

    // if we try to use iter again, it won't work. The following line
    // gives "error: use of moved value: `iter`
    // assert_eq!(iter.next(), None);

    // let's try that again
    let a = [1, 2, 3];

    let mut iter = a.into_iter();

    // instead, we add in a .by_ref()
    let sum: i32 = iter.by_ref()
                       .take(2)
                       .fold(0, |acc, &i| acc + i );

    assert_eq!(sum, 3);

    // now this is just fine:
    assert_eq!(iter.next(), Some(&3));
    assert_eq!(iter.next(), None);Run

### `fn collect<B>(self) -> B where B: FromIterator<Self::Item>`

Transforms an iterator into a collection.

`collect()` can take anything iterable, and turn it into a relevant collection. This is one of the more powerful methods in the standard library, used in a variety of contexts.

The most basic pattern in which `collect()` is used is to turn one collection into another. You take a collection, call `iter()` on it, do a bunch of transformations, and then `collect()` at the end.

One of the keys to `collect()`'s power is that many things you might not think of as 'collections' actually are. For example, a `String` is a collection of `char`s. And a collection of `Result<T, E>` can be thought of as single `Result<Collection<T>, E>`. See the examples below for more.

Because `collect()` is so general, it can cause problems with type inference. As such, `collect()` is one of the few times you'll see the syntax affectionately known as the 'turbofish': `::<>`. This helps the inference algorithm understand specifically which collection you're trying to collect into.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let doubled: Vec<i32> = a.iter()
                             .map(|&x| x * 2)
                             .collect();

    assert_eq!(vec![2, 4, 6], doubled);Run

Note that we needed the `: Vec<i32>` on the left-hand side. This is because we could collect into, for example, a `VecDeque<T>` instead:

    use std::collections::VecDeque;

    let a = [1, 2, 3];

    let doubled: VecDeque<i32> = a.iter()
                                  .map(|&x| x * 2)
                                  .collect();

    assert_eq!(2, doubled[0]);
    assert_eq!(4, doubled[1]);
    assert_eq!(6, doubled[2]);Run

Using the 'turbofish' instead of annotating `doubled`:

    let a = [1, 2, 3];

    let doubled = a.iter()
                   .map(|&x| x * 2)
                   .collect::<Vec<i32>>();

    assert_eq!(vec![2, 4, 6], doubled);Run

Because `collect()` cares about what you're collecting into, you can still use a partial type hint, `_`, with the turbofish:

    let a = [1, 2, 3];

    let doubled = a.iter()
                   .map(|&x| x * 2)
                   .collect::<Vec<_>>();

    assert_eq!(vec![2, 4, 6], doubled);Run

Using `collect()` to make a `String`:

    let chars = ['g', 'd', 'k', 'k', 'n'];

    let hello: String = chars.iter()
                             .map(|&x| x as u8)
                             .map(|x| (x + 1) as char)
                             .collect();

    assert_eq!("hello", hello);Run

If you have a list of `Result<T, E>`s, you can use `collect()` to see if any of them failed:

    let results = [Ok(1), Err("nope"), Ok(3), Err("bad")];

    let result: Result<Vec<_>, &str> = results.iter().cloned().collect();

    // gives us the first error
    assert_eq!(Err("nope"), result);

    let results = [Ok(1), Ok(3)];

    let result: Result<Vec<_>, &str> = results.iter().cloned().collect();

    // gives us the list of answers
    assert_eq!(Ok(vec![1, 3]), result);Run

### `fn partition<B, F>(self, f: F) -> (B, B) where B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool`

Consumes an iterator, creating two collections from it.

The predicate passed to `partition()` can return `true`, or `false`. `partition()` returns a pair, all of the elements for which it returned `true`, and all of the elements for which it returned `false`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let (even, odd): (Vec<i32>, Vec<i32>) = a.into_iter()
                                             .partition(|&n| n % 2 == 0);

    assert_eq!(even, vec![2]);
    assert_eq!(odd, vec![1, 3]);Run

### `fn fold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B`

An iterator adaptor that applies a function, producing a single, final value.

`fold()` takes two arguments: an initial value, and a closure with two arguments: an 'accumulator', and an element. The closure returns the value that the accumulator should have for the next iteration.

The initial value is the value the accumulator will have on the first call.

After applying this closure to every element of the iterator, `fold()` returns the accumulator.

This operation is sometimes called 'reduce' or 'inject'.

Folding is useful whenever you have a collection of something, and want to produce a single value from it.

# Examples

Basic usage:

    let a = [1, 2, 3];

    // the sum of all of the elements of a
    let sum = a.iter()
               .fold(0, |acc, &x| acc + x);

    assert_eq!(sum, 6);Run

Let's walk through each step of the iteration here:

element | acc | x | result
--- | --- | --- | ---
| 0 |  |
1 | 0 | 1 | 1
2 | 1 | 2 | 3
3 | 3 | 3 | 6

And so, our final result, `6`.

It's common for people who haven't used iterators a lot to use a `for` loop with a list of things to build up a result. Those can be turned into `fold()`s:

    let numbers = [1, 2, 3, 4, 5];

    let mut result = 0;

    // for loop:
    for i in &numbers {
        result = result + i;
    }

    // fold:
    let result2 = numbers.iter().fold(0, |acc, &x| acc + x);

    // they're the same
    assert_eq!(result, result2);Run

### `fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool`

Tests if every element of the iterator matches a predicate.

`all()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if they all return `true`, then so does `all()`. If any of them return `false`, it returns `false`.

`all()` is short-circuiting; in other words, it will stop processing as soon as it finds a `false`, given that no matter what else happens, the result will also be `false`.

An empty iterator returns `true`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert!(a.iter().all(|&x| x > 0));

    assert!(!a.iter().all(|&x| x > 2));Run

Stopping at the first `false`:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    assert!(!iter.all(|&x| x != 2));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(&3));Run

### `fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool`

Tests if any element of the iterator matches a predicate.

`any()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if any of them return `true`, then so does `any()`. If they all return `false`, it returns `false`.

`any()` is short-circuiting; in other words, it will stop processing as soon as it finds a `true`, given that no matter what else happens, the result will also be `true`.

An empty iterator returns `false`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert!(a.iter().any(|&x| x > 0));

    assert!(!a.iter().any(|&x| x > 5));Run

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    assert!(iter.any(|&x| x != 2));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(&2));Run

### `fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool`

Searches for an element of an iterator that satisfies a predicate.

`find()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if any of them return `true`, then `find()` returns `Some(element)`. If they all return `false`, it returns `None`.

`find()` is short-circuiting; in other words, it will stop processing as soon as the closure returns `true`.

Because `find()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation where the argument is a double reference. You can see this effect in the examples below, with `&&x`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.iter().find(|&&x| x == 2), Some(&2));

    assert_eq!(a.iter().find(|&&x| x == 5), None);Run

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    assert_eq!(iter.find(|&&x| x == 2), Some(&2));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(&3));Run

### `fn position<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool`

Searches for an element in an iterator, returning its index.

`position()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if one of them returns `true`, then `position()` returns `Some(index)`. If all of them return `false`, it returns `None`.

`position()` is short-circuiting; in other words, it will stop processing as soon as it finds a `true`.

# Overflow Behavior

The method does no guarding against overflows, so if there are more than `usize::MAX` non-matching elements, it either produces the wrong result or panics. If debug assertions are enabled, a panic is guaranteed.

# Panics

This function might panic if the iterator has more than `usize::MAX` non-matching elements.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.iter().position(|&x| x == 2), Some(1));

    assert_eq!(a.iter().position(|&x| x == 5), None);Run

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    assert_eq!(iter.position(|&x| x == 2), Some(1));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(&3));Run

### `fn rposition<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool, Self: ExactSizeIterator + DoubleEndedIterator`

Searches for an element in an iterator from the right, returning its index.

`rposition()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, starting from the end, and if one of them returns `true`, then `rposition()` returns `Some(index)`. If all of them return `false`, it returns `None`.

`rposition()` is short-circuiting; in other words, it will stop processing as soon as it finds a `true`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.iter().rposition(|&x| x == 3), Some(2));

    assert_eq!(a.iter().rposition(|&x| x == 5), None);Run

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.iter();

    assert_eq!(iter.rposition(|&x| x == 2), Some(1));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(&1));Run

### `fn max(self) -> Option<Self::Item> where Self::Item: Ord`

Returns the maximum element of an iterator.

If the two elements are equally maximum, the latest element is returned.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.iter().max(), Some(&3));Run

### `fn min(self) -> Option<Self::Item> where Self::Item: Ord`

Returns the minimum element of an iterator.

If the two elements are equally minimum, the first element is returned.

# Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.iter().min(), Some(&1));Run

### `fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B`
1.6.0

Returns the element that gives the maximum value from the specified function.

Returns the rightmost element if the comparison determines two elements to be equally maximum.

# Examples

    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10);Run

### `fn max_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering`

Unstable (`iter_max_by` #36105)

Returns the element that gives the maximum value with respect to the specified comparison function.

Returns the rightmost element if the comparison determines two elements to be equally maximum.

# Examples

    #![feature(iter_max_by)]
    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);Run

### `fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B`
1.6.0

Returns the element that gives the minimum value from the specified function.

Returns the latest element if the comparison determines two elements to be equally minimum.

# Examples

    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0);Run

### `fn min_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering`

Unstable (`iter_min_by` #36105)

Returns the element that gives the minimum value with respect to the specified comparison function.

Returns the latest element if the comparison determines two elements to be equally minimum.

# Examples

    #![feature(iter_min_by)]
    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);Run

### `fn rev(self) -> Rev<Self> where Self: DoubleEndedIterator`

Reverses an iterator's direction.

Usually, iterators iterate from left to right. After using `rev()`, an iterator will instead iterate from right to left.

This is only possible if the iterator has an end, so `rev()` only works on `DoubleEndedIterator`s.

# Examples

    let a = [1, 2, 3];

    let mut iter = a.iter().rev();

    assert_eq!(iter.next(), Some(&3));
    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), Some(&1));

    assert_eq!(iter.next(), None);Run

### `fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Iterator<Item=(A, B)>`

Converts an iterator of pairs into a pair of containers.

`unzip()` consumes an entire iterator of pairs, producing two collections: one from the left elements of the pairs, and one from the right elements.

This function is, in some sense, the opposite of `zip()`.

# Examples

Basic usage:

    let a = [(1, 2), (3, 4)];

    let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip();

    assert_eq!(left, [1, 3]);
    assert_eq!(right, [2, 4]);Run

### `fn cloned<'a, T>(self) -> Cloned<Self> where Self: Iterator<Item=&'a T>, T: 'a + Clone`

Creates an iterator which `clone()`s all of its elements.

This is useful when you have an iterator over `&T`, but you need an iterator over `T`.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let v_cloned: Vec<_> = a.iter().cloned().collect();

    // cloned is the same as .map(|&x| x), for integers
    let v_map: Vec<_> = a.iter().map(|&x| x).collect();

    assert_eq!(v_cloned, vec![1, 2, 3]);
    assert_eq!(v_map, vec![1, 2, 3]);Run

### `fn cycle(self) -> Cycle<Self> where Self: Clone`

Repeats an iterator endlessly.

Instead of stopping at `None`, the iterator will instead start again, from the beginning. After iterating again, it will start at the beginning again. And again. And again. Forever.

# Examples

Basic usage:

    let a = [1, 2, 3];

    let mut it = a.iter().cycle();

    assert_eq!(it.next(), Some(&1));
    assert_eq!(it.next(), Some(&2));
    assert_eq!(it.next(), Some(&3));
    assert_eq!(it.next(), Some(&1));
    assert_eq!(it.next(), Some(&2));
    assert_eq!(it.next(), Some(&3));
    assert_eq!(it.next(), Some(&1));Run

### `fn sum<S>(self) -> S where S: Sum<Self::Item>`
1.11.0

Sums the elements of an iterator.

Takes each element, adds them together, and returns the result.

An empty iterator returns the zero value of the type.

# Panics

When calling `sum` and a primitive integer type is being returned, this method will panic if the computation overflows and debug assertions are enabled.

# Examples

Basic usage:

    let a = [1, 2, 3];
    let sum: i32 = a.iter().sum();

    assert_eq!(sum, 6);Run

### `fn product<P>(self) -> P where P: Product<Self::Item>`
1.11.0

Iterates over the entire iterator, multiplying all the elements

An empty iterator returns the one value of the type.

# Panics

When calling `product` and a primitive integer type is being returned, method will panic if the computation overflows and debug assertions are enabled.

# Examples

    fn factorial(n: u32) -> u32 {
        (1..).take_while(|&i| i <= n).product()
    }
    assert_eq!(factorial(0), 1);
    assert_eq!(factorial(1), 1);
    assert_eq!(factorial(5), 120);Run

### `fn cmp<I>(self, other: I) -> Ordering where I: IntoIterator<Item=Self::Item>, Self::Item: Ord`
1.5.0

Lexicographically compares the elements of this `Iterator` with those of another.

### `fn partial_cmp<I>(self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item>`
1.5.0

Lexicographically compares the elements of this `Iterator` with those of another.

### `fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>`
1.5.0

Determines if the elements of this `Iterator` are equal to those of another.

### `fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>`
1.5.0

Determines if the elements of this `Iterator` are unequal to those of another.

### `fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>`
1.5.0

Determines if the elements of this `Iterator` are lexicographically less than those of another.

### `fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>`
1.5.0

Determines if the elements of this `Iterator` are lexicographically less or equal to those of another.

### `fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>`
1.5.0

Determines if the elements of this `Iterator` are lexicographically greater than those of another.

### `fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>`
1.5.0

Determines if the elements of this `Iterator` are lexicographically greater than or equal to those of another.

## Implementors

- `impl<'a, T, R> Iterator for Generator<'a, T, R> where R: Rng, T: Rand`
- `impl<'a, R> Iterator for AsciiGenerator<'a, R> where R: Rng`
- `impl Iterator for EscapeUnicode`
- `impl Iterator for EscapeDefault`
- `impl Iterator for EscapeDebug`
- `impl<I> Iterator for DecodeUtf8<I> where I: Iterator<Item=u8>`
- `impl<'a, I> Iterator for &'a mut I where I: Iterator + ?Sized`
- `impl<A> Iterator for StepBy<A, RangeFrom<A>> where A: Clone, &'a A: Add<&'a A>, &'a A::Output == A`
- `impl<A> Iterator for StepBy<A, Range<A>> where A: Clone + Step`
- `impl<A> Iterator for StepBy<A, RangeInclusive<A>> where A: Clone + Step`
- `impl<A> Iterator for Range<A> where A: Step, &'a A: Add<&'a A>, &'a A::Output == A`
- `impl<A> Iterator for RangeFrom<A> where A: Step, &'a A: Add<&'a A>, &'a A::Output == A`
- `impl<A> Iterator for RangeInclusive<A> where A: Step, &'a A: Add<&'a A>, &'a A::Output == A`
- `impl<A> Iterator for Repeat<A> where A: Clone`
- `impl<T> Iterator for Empty<T>`
- `impl<T> Iterator for Once<T>`
- `impl<I> Iterator for Rev<I> where I: DoubleEndedIterator`
- `impl<'a, I, T> Iterator for Cloned<I> where I: Iterator<Item=&'a T>, T: 'a + Clone`
- `impl<I> Iterator for Cycle<I> where I: Clone + Iterator`
- `impl<A, B> Iterator for Chain<A, B> where A: Iterator, B: Iterator<Item=A::Item>`
- `impl<A, B> Iterator for Zip<A, B> where A: Iterator, B: Iterator`
- `impl<B, I, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B, I: Iterator`
- `impl<I, P> Iterator for Filter<I, P> where I: Iterator, P: FnMut(&I::Item) -> bool`
- `impl<B, I, F> Iterator for FilterMap<I, F> where F: FnMut(I::Item) -> Option<B>, I: Iterator`
- `impl<I> Iterator for Enumerate<I> where I: Iterator`
- `impl<I> Iterator for Peekable<I> where I: Iterator`
- `impl<I, P> Iterator for SkipWhile<I, P> where I: Iterator, P: FnMut(&I::Item) -> bool`
- `impl<I, P> Iterator for TakeWhile<I, P> where I: Iterator, P: FnMut(&I::Item) -> bool`
- `impl<I> Iterator for Skip<I> where I: Iterator`
- `impl<I> Iterator for Take<I> where I: Iterator`
- `impl<B, I, St, F> Iterator for Scan<I, St, F> where F: FnMut(&mut St, I::Item) -> Option<B>, I: Iterator`
- `impl<I, U, F> Iterator for FlatMap<I, U, F> where F: FnMut(I::Item) -> U, I: Iterator, U: IntoIterator`
- `impl<I> Iterator for Fuse<I> where I: Iterator`
- `impl<I> Iterator for Fuse<I> where I: FusedIterator`
- `impl<I, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) -> (), I: Iterator`
- `impl<'a, A> Iterator for Iter<'a, A>`
- `impl<'a, A> Iterator for IterMut<'a, A>`
- `impl<A> Iterator for IntoIter<A>`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<'a, T> Iterator for IterMut<'a, T>`
- `impl<T> Iterator for IntoIter<T>`
- `impl<'a, T, P> Iterator for Split<'a, T, P> where P: FnMut(&T) -> bool`
- `impl<'a, T, P> Iterator for SplitMut<'a, T, P> where P: FnMut(&T) -> bool`
- `impl<'a, T> Iterator for Windows<'a, T>`
- `impl<'a, T> Iterator for Chunks<'a, T>`
- `impl<'a, T> Iterator for ChunksMut<'a, T>`
- `impl<'a> Iterator for Chars<'a>`
- `impl<'a> Iterator for CharIndices<'a>`
- `impl<'a> Iterator for Bytes<'a>`
- `impl<'a> Iterator for Lines<'a>`
- `impl<'a> Iterator for LinesAny<'a>`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<'a, T> Iterator for IterMut<'a, T>`
- `impl<'a, T, P> Iterator for SplitN<'a, T, P> where P: FnMut(&T) -> bool`
- `impl<'a, T, P> Iterator for RSplitN<'a, T, P> where P: FnMut(&T) -> bool`
- `impl<'a, T, P> Iterator for SplitNMut<'a, T, P> where P: FnMut(&T) -> bool`
- `impl<'a, T, P> Iterator for RSplitNMut<'a, T, P> where P: FnMut(&T) -> bool`
- `impl<'a, P> Iterator for Split<'a, P> where P: Pattern<'a>`
- `impl<'a, P> Iterator for RSplit<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`
- `impl<'a, P> Iterator for SplitTerminator<'a, P> where P: Pattern<'a>`
- `impl<'a, P> Iterator for RSplitTerminator<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`
- `impl<'a, P> Iterator for SplitN<'a, P> where P: Pattern<'a>`
- `impl<'a, P> Iterator for RSplitN<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`
- `impl<'a, P> Iterator for MatchIndices<'a, P> where P: Pattern<'a>`
- `impl<'a, P> Iterator for RMatchIndices<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`
- `impl<'a, P> Iterator for Matches<'a, P> where P: Pattern<'a>`
- `impl<'a, P> Iterator for RMatches<'a, P> where P: Pattern<'a>, P::Searcher: ReverseSearcher<'a>`
- `impl<I> Iterator for Utf16Encoder<I> where I: Iterator<Item=char>`
- `impl<'a> Iterator for SplitWhitespace<'a>`
- `impl Iterator for ToLowercase`
- `impl Iterator for ToUppercase`
- `impl<I> Iterator for DecodeUtf16<I> where I: Iterator<Item=u16>`
- `impl<I> Iterator for Box<I> where I: Iterator + ?Sized`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<T> Iterator for IntoIter<T>`
- `impl<'a, T> Iterator for Drain<'a, T> where T: 'a`
- `impl<'a, K, V> Iterator for Iter<'a, K, V> where K: 'a, V: 'a`
- `impl<'a, K, V> Iterator for IterMut<'a, K, V> where K: 'a, V: 'a`
- `impl<K, V> Iterator for IntoIter<K, V>`
- `impl<'a, K, V> Iterator for Keys<'a, K, V>`
- `impl<'a, K, V> Iterator for Values<'a, K, V>`
- `impl<'a, K, V> Iterator for Range<'a, K, V>`
- `impl<'a, K, V> Iterator for ValuesMut<'a, K, V>`
- `impl<'a, K, V> Iterator for RangeMut<'a, K, V>`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<T> Iterator for IntoIter<T>`
- `impl<'a, T> Iterator for Range<'a, T>`
- `impl<'a, T> Iterator for Difference<'a, T> where T: Ord`
- `impl<'a, T> Iterator for SymmetricDifference<'a, T> where T: Ord`
- `impl<'a, T> Iterator for Intersection<'a, T> where T: Ord`
- `impl<'a, T> Iterator for Union<'a, T> where T: Ord`
- `impl<E> Iterator for Iter<E> where E: CLike`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<'a, T> Iterator for IterMut<'a, T>`
- `impl<T> Iterator for IntoIter<T>`
- `impl<'a> Iterator for EncodeUtf16<'a>`
- `impl<'a> Iterator for Drain<'a>`
- `impl<T> Iterator for IntoIter<T>`
- `impl<'a, T> Iterator for Drain<'a, T>`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<'a, T> Iterator for IterMut<'a, T>`
- `impl<T> Iterator for IntoIter<T>`
- `impl<'a, T> Iterator for Drain<'a, T> where T: 'a`
- `impl Iterator for EscapeDefault`
- `impl<'a, K, V> Iterator for Iter<'a, K, V>`
- `impl<'a, K, V> Iterator for IterMut<'a, K, V>`
- `impl<K, V> Iterator for IntoIter<K, V>`
- `impl<'a, K, V> Iterator for Keys<'a, K, V>`
- `impl<'a, K, V> Iterator for Values<'a, K, V>`
- `impl<'a, K, V> Iterator for ValuesMut<'a, K, V>`
- `impl<'a, K, V> Iterator for Drain<'a, K, V>`
- `impl<'a, K> Iterator for Iter<'a, K>`
- `impl<K> Iterator for IntoIter<K>`
- `impl<'a, K> Iterator for Drain<'a, K>`
- `impl<'a, T, S> Iterator for Intersection<'a, T, S> where T: Eq + Hash, S: BuildHasher`
- `impl<'a, T, S> Iterator for Difference<'a, T, S> where T: Eq + Hash, S: BuildHasher`
- `impl<'a, T, S> Iterator for SymmetricDifference<'a, T, S> where T: Eq + Hash, S: BuildHasher`
- `impl<'a, T, S> Iterator for Union<'a, T, S> where T: Eq + Hash, S: BuildHasher`
- `impl Iterator for Vars`
- `impl Iterator for VarsOs`
- `impl<'a> Iterator for SplitPaths<'a>`
- `impl Iterator for Args`
- `impl Iterator for ArgsOs`
- `impl Iterator for ReadDir`
- `impl<R: Read> Iterator for Bytes<R>`
- `impl<R: Read> Iterator for Chars<R>`
- `impl<B: BufRead> Iterator for Split<B>`
- `impl<B: BufRead> Iterator for Lines<B>`
- `impl<'a> Iterator for Incoming<'a>`
- `impl Iterator for LookupHost`
- `impl<'a> Iterator for Incoming<'a>`
- `impl<'a> Iterator for Iter<'a>`
- `impl<'a> Iterator for Components<'a>`
- `impl<'a, T> Iterator for Iter<'a, T>`
- `impl<'a, T> Iterator for TryIter<'a, T>`
- `impl<T> Iterator for IntoIter<T>`

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