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

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:

fn main() { 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()); }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());

## 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:

fn main() { let a = [1, 2, 3]; let iter = a.iter(); assert_eq!((3, Some(3)), iter.size_hint()); }let a = [1, 2, 3]; let iter = a.iter(); assert_eq!((3, Some(3)), iter.size_hint());

A more complex example:

fn main() { // 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()); }// 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());

Returning `None`

for an upper bound:

// an infinite iterator has no upper bound let iter = 0..; assert_eq!((0, None), iter.size_hint());

`fn count(self) -> usize where Self: Sized`

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:

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().count(), 3); let a = [1, 2, 3, 4, 5]; assert_eq!(a.iter().count(), 5); }let a = [1, 2, 3]; assert_eq!(a.iter().count(), 3); let a = [1, 2, 3, 4, 5]; assert_eq!(a.iter().count(), 5);

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

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:

fn main() { 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)); }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));

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

Consumes the `n`

first elements of the iterator, then returns the
`next()`

one.

This method will evaluate the iterator `n`

times, discarding those elements.
After it does so, it will call `next()`

and return its value.

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:

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().nth(1), Some(&2)); }let a = [1, 2, 3]; assert_eq!(a.iter().nth(1), Some(&2));

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);

Returning `None`

if there are less than `n + 1`

elements:

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

`fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where Self: Sized, 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:

fn main() { 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); }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);

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);

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

fn main() { 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); }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);

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);

`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]);

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

fn main() { 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); }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);

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); }

`fn filter<P>(self, predicate: P) -> Filter<Self, P> where Self: Sized, 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:

fn main() { 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); }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);

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);

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

fn main() { 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); }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);

or both:

fn main() { 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); }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);

of these layers.

`fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where Self: Sized, 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:

fn main() { 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); }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);

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);

There's an extra layer of `Some`

in there.

`fn enumerate(self) -> Enumerate<Self> where Self: Sized`

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

fn main() { 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); }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);

`fn peekable(self) -> Peekable<Self> where Self: Sized`

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:

fn main() { 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); }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);

`fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where Self: Sized, 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:

fn main() { 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); }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);

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);

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);

`fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where Self: Sized, 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:

fn main() { 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); }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);

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);

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);

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]);

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> where Self: Sized`

Creates an iterator that skips the first `n`

elements.

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

# Examples

Basic usage:

fn main() { let a = [1, 2, 3]; let mut iter = a.iter().skip(2); assert_eq!(iter.next(), Some(&3)); assert_eq!(iter.next(), None); }let a = [1, 2, 3]; let mut iter = a.iter().skip(2); assert_eq!(iter.next(), Some(&3)); assert_eq!(iter.next(), None);

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

Creates an iterator that yields its first `n`

elements.

# Examples

Basic usage:

fn main() { 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); }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);

`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);

`fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where Self: Sized, 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:

fn main() { 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); }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);

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

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:

fn main() { let words = ["alpha", "beta", "gamma"]; // chars() returns an iterator let merged: String = words.iter() .flat_map(|s| s.chars()) .collect(); assert_eq!(merged, "alphabetagamma"); }let words = ["alpha", "beta", "gamma"]; // chars() returns an iterator let merged: String = words.iter() .flat_map(|s| s.chars()) .collect(); assert_eq!(merged, "alphabetagamma");

`fn fuse(self) -> Fuse<Self> where Self: Sized`

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:

fn main() { // 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); }// 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);

`fn inspect<F>(self, f: F) -> Inspect<Self, F> where Self: Sized, 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:

fn main() { 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); }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);

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 where Self: Sized`

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:

fn main() { 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); }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);

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

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:

fn main() { let a = [1, 2, 3]; let doubled: Vec<i32> = a.iter() .map(|&x| x * 2) .collect(); assert_eq!(vec![2, 4, 6], doubled); }let a = [1, 2, 3]; let doubled: Vec<i32> = a.iter() .map(|&x| x * 2) .collect(); assert_eq!(vec![2, 4, 6], doubled);

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]);

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);

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);

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);

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);

`fn partition<B, F>(self, f: F) -> (B, B) where Self: Sized, 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:

fn main() { 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]); }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]);

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

fn main() { 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); }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);

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);

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

fn main() { let a = [1, 2, 3]; assert!(a.iter().all(|&x| x > 0)); assert!(!a.iter().all(|&x| x > 2)); }let a = [1, 2, 3]; assert!(a.iter().all(|&x| x > 0)); assert!(!a.iter().all(|&x| x > 2));

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));

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

fn main() { let a = [1, 2, 3]; assert!(a.iter().any(|&x| x > 0)); assert!(!a.iter().any(|&x| x > 5)); }let a = [1, 2, 3]; assert!(a.iter().any(|&x| x > 0)); assert!(!a.iter().any(|&x| x > 5));

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));

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

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); assert_eq!(a.iter().find(|&&x| x == 5), None); }let a = [1, 2, 3]; assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); assert_eq!(a.iter().find(|&&x| x == 5), None);

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));

`fn position<P>(&mut self, predicate: P) -> Option<usize> where Self: Sized, 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:

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().position(|&x| x == 2), Some(1)); assert_eq!(a.iter().position(|&x| x == 5), None); }let a = [1, 2, 3]; assert_eq!(a.iter().position(|&x| x == 2), Some(1)); assert_eq!(a.iter().position(|&x| x == 5), None);

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));

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

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); assert_eq!(a.iter().rposition(|&x| x == 5), None); }let a = [1, 2, 3]; assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); assert_eq!(a.iter().rposition(|&x| x == 5), None);

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));

`fn max(self) -> Option<Self::Item> where Self: Sized, 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:

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().max(), Some(&3)); }let a = [1, 2, 3]; assert_eq!(a.iter().max(), Some(&3));

`fn min(self) -> Option<Self::Item> where Self: Sized, 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:

fn main() { let a = [1, 2, 3]; assert_eq!(a.iter().min(), Some(&1)); }let a = [1, 2, 3]; assert_eq!(a.iter().min(), Some(&1));

`fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> where Self: Sized, 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

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

`fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> where Self: Sized, 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

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

`fn rev(self) -> Rev<Self> where Self: Sized + 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

fn main() { 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); }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);

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

fn main() { 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]); }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]);

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

fn main() { 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]); }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]);

`fn cycle(self) -> Cycle<Self> where Self: Sized + 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:

fn main() { 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)); }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));

`fn sum<S>(self) -> S where S: Add<Self::Item, Output=S> + Zero, Self: Sized`

*Unstable (*

`iter_arith`

#27739): bounds recently changed

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.

# Examples

Basic usage:

#![feature(iter_arith)] fn main() { let a = [1, 2, 3]; let sum: i32 = a.iter().sum(); assert_eq!(sum, 6); }#![feature(iter_arith)] let a = [1, 2, 3]; let sum: i32 = a.iter().sum(); assert_eq!(sum, 6);

`fn product<P>(self) -> P where P: Mul<Self::Item, Output=P> + One, Self: Sized`

*Unstable (*

`iter_arith`

#27739): bounds recently changed

Iterates over the entire iterator, multiplying all the elements

An empty iterator returns the one value of the type.

# Examples

#![feature(iter_arith)] fn main() { 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); }#![feature(iter_arith)] 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);

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

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>, Self: Sized`

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>, Self: Sized`

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>, Self: Sized`

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>, Self: Sized`

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>, Self: Sized`

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>, Self: Sized`

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>, Self: Sized`

1.5.0

Determines if the elements of this `Iterator`

are lexicographically
greater than or equal to those of another.

## Implementors

`impl Iterator for EscapeUnicode`

`impl Iterator for EscapeDefault`

`impl Iterator for EncodeUtf8`

`impl Iterator for EncodeUtf16`

`impl<'a, I: Iterator + ?Sized> Iterator for &'a mut I`

`impl<A> Iterator for StepBy<A, RangeFrom<A>> where A: Clone, &'a A: Add<&'a A, Output=A>`

`impl<A: Step + Zero + Clone> Iterator for StepBy<A, Range<A>>`

`impl<A: Step + Zero + Clone> Iterator for StepBy<A, RangeInclusive<A>>`

`impl<A: Step + One> Iterator for Range<A> where &'a A: Add<&'a A, Output=A>`

`impl<A: Step + One> Iterator for RangeFrom<A> where &'a A: Add<&'a A, Output=A>`

`impl<A: Step + One> Iterator for RangeInclusive<A> where &'a A: Add<&'a A, Output=A>`

`impl<A: Clone> Iterator for Repeat<A>`

`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: 'a> Iterator for Cloned<I> where I: Iterator<Item=&'a T>, T: 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: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B`

`impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool`

`impl<B, I: Iterator, F> Iterator for FilterMap<I, F> where F: FnMut(I::Item) -> Option<B>`

`impl<I> Iterator for Enumerate<I> where I: Iterator`

`impl<I: Iterator> Iterator for Peekable<I>`

`impl<I: Iterator, P> Iterator for SkipWhile<I, P> where P: FnMut(&I::Item) -> bool`

`impl<I: Iterator, P> Iterator for TakeWhile<I, P> where 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 I: Iterator, F: FnMut(&mut St, I::Item) -> Option<B>`

`impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F> where F: FnMut(I::Item) -> U`

`impl<I> Iterator for Fuse<I> where I: Iterator`

`impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item)`

`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> Iterator for Iter<'a, T>`

`impl<'a, T> Iterator for IterMut<'a, 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, 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, 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, P: Pattern<'a>> Iterator for Split<'a, P>`

`impl<'a, P: Pattern<'a>> Iterator for RSplit<'a, P> where P::Searcher: ReverseSearcher<'a>`

`impl<'a, P: Pattern<'a>> Iterator for SplitTerminator<'a, P>`

`impl<'a, P: Pattern<'a>> Iterator for RSplitTerminator<'a, P> where P::Searcher: ReverseSearcher<'a>`

`impl<'a, P: Pattern<'a>> Iterator for SplitN<'a, P>`

`impl<'a, P: Pattern<'a>> Iterator for RSplitN<'a, P> where P::Searcher: ReverseSearcher<'a>`

`impl<'a, P: Pattern<'a>> Iterator for MatchIndices<'a, P>`

`impl<'a, P: Pattern<'a>> Iterator for RMatchIndices<'a, P> where P::Searcher: ReverseSearcher<'a>`

`impl<'a, P: Pattern<'a>> Iterator for Matches<'a, P>`

`impl<'a, P: Pattern<'a>> Iterator for RMatches<'a, P> where P::Searcher: ReverseSearcher<'a>`

`impl<'a> Iterator for Lines<'a>`

`impl<'a> Iterator for LinesAny<'a>`