# Struct std::iter::Map1.0.0[−][src]

```#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct Map<I, F> { /* fields omitted */ }```

An iterator that maps the values of `iter` with `f`.

This `struct` is created by the `map` method on `Iterator`. See its documentation for more.

The `map` iterator implements `DoubleEndedIterator`, meaning that you can also `map` backwards:

```let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();

assert_eq!(v, [4, 3, 2]);Run```

But if your closure has state, iterating backwards may act in a way you do not expect. Let's go through an example. First, in the forward direction:

```let mut c = 0;

for pair in vec!['a', 'b', 'c'].into_iter()
.map(|letter| { c += 1; (letter, c) }) {
println!("{:?}", pair);
}Run```

This will print "('a', 1), ('b', 2), ('c', 3)".

Now consider this twist where we add a call to `rev`. This version will print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed, but the values of the counter still go in order. This is because `map()` is still being called lazily on each item, but we are popping items off the back of the vector now, instead of shifting them from the front.

```let mut c = 0;

for pair in vec!['a', 'b', 'c'].into_iter()
.map(|letter| { c += 1; (letter, c) })
.rev() {
println!("{:?}", pair);
}Run```

## Trait Implementations

### `impl<I, F> Debug for Map<I, F> where    I: Debug, `1.9.0[src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `impl<B, I, F> DoubleEndedIterator for Map<I, F> where    F: FnMut(<I as Iterator>::Item) -> B,    I: DoubleEndedIterator, `[src]

#### `fn next_back(&mut self) -> Option<B>`[src]

Removes and returns an element from the end of the iterator. Read more

#### `fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R where    G: FnMut(Acc, <Map<I, F> as Iterator>::Item) -> R,    R: Try<Ok = Acc>,    Map<I, F>: Sized, `[src]

This is the reverse version of [`try_fold()`]: it takes elements starting from the back of the iterator. Read more

#### `fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc where    G: FnMut(Acc, <Map<I, F> as Iterator>::Item) -> Acc, `[src]

An iterator method that reduces the iterator's elements to a single, final value, starting from the back. Read more

#### `fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where    P: FnMut(&Self::Item) -> bool, `1.27.0[src]

Searches for an element of an iterator from the back that satisfies a predicate. Read more

### `impl<B, I, F> ExactSizeIterator for Map<I, F> where    F: FnMut(<I as Iterator>::Item) -> B,    I: ExactSizeIterator, `[src]

#### `fn len(&self) -> usize`[src]

Returns the exact number of times the iterator will iterate. Read more

#### `fn is_empty(&self) -> bool`[src]

🔬 This is a nightly-only experimental API. (`exact_size_is_empty `#35428)

Returns whether the iterator is empty. Read more

### `impl<I, F> Clone for Map<I, F> where    F: Clone,    I: Clone, `[src]

#### ⓘImportant traits for Map<I, F>### Important traits for Map<I, F> `impl<B, I, F> Iterator for Map<I, F> where    F: FnMut(<I as Iterator>::Item) -> B,    I: Iterator,  type Item = B;``fn clone(&self) -> Map<I, F>`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`[src]

Performs copy-assignment from `source`. Read more

### `impl<B, I, F> Iterator for Map<I, F> where    F: FnMut(<I as Iterator>::Item) -> B,    I: Iterator, `[src]

#### `type Item = B`

The type of the elements being iterated over.

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

Returns the bounds on the remaining length of the iterator. Read more

#### `fn try_fold<Acc, G, R>(&mut self, init: Acc, g: G) -> R where    G: FnMut(Acc, <Map<I, F> as Iterator>::Item) -> R,    R: Try<Ok = Acc>,    Map<I, F>: Sized, `[src]

An iterator method that applies a function as long as it returns successfully, producing a single, final value. Read more

#### `fn fold<Acc, G>(self, init: Acc, g: G) -> Acc where    G: FnMut(Acc, <Map<I, F> as Iterator>::Item) -> Acc, `[src]

An iterator method that applies a function, producing a single, final value. Read more

#### `fn count(self) -> usize`[src]

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

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

Consumes the iterator, returning the last element. Read more

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

Returns the `n`th element of the iterator. Read more

#### ⓘImportant traits for StepBy<I>### Important traits for StepBy<I> `impl<I> Iterator for StepBy<I> where    I: Iterator,  type Item = <I as Iterator>::Item;``fn step_by(self, step: usize) -> StepBy<Self>`1.28.0[src]

Creates an iterator starting at the same point, but stepping by the given amount at each iteration. Read more

#### ⓘImportant traits for Chain<A, B>### Important traits for Chain<A, B> `impl<A, B> Iterator for Chain<A, B> where    A: Iterator,    B: Iterator<Item = <A as Iterator>::Item>,  type Item = <A as Iterator>::Item;``fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> where    U: IntoIterator<Item = Self::Item>, `[src]

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

#### ⓘImportant traits for Zip<A, B>### Important traits for Zip<A, B> `impl<A, B> Iterator for Zip<A, B> where    A: Iterator,    B: Iterator,  type Item = (<A as Iterator>::Item, <B as Iterator>::Item);``fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> where    U: IntoIterator, `[src]

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

#### ⓘImportant traits for Map<I, F>### Important traits for Map<I, F> `impl<B, I, F> Iterator for Map<I, F> where    F: FnMut(<I as Iterator>::Item) -> B,    I: Iterator,  type Item = B;``fn map<B, F>(self, f: F) -> Map<Self, F> where    F: FnMut(Self::Item) -> B, `[src]

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

#### `fn for_each<F>(self, f: F) where    F: FnMut(Self::Item), `1.21.0[src]

Calls a closure on each element of an iterator. Read more

#### ⓘImportant traits for Filter<I, P>### Important traits for Filter<I, P> `impl<I, P> Iterator for Filter<I, P> where    I: Iterator,    P: FnMut(&<I as Iterator>::Item) -> bool,  type Item = <I as Iterator>::Item;``fn filter<P>(self, predicate: P) -> Filter<Self, P> where    P: FnMut(&Self::Item) -> bool, `[src]

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

#### ⓘImportant traits for FilterMap<I, F>### Important traits for FilterMap<I, F> `impl<B, I, F> Iterator for FilterMap<I, F> where    F: FnMut(<I as Iterator>::Item) -> Option<B>,    I: Iterator,  type Item = B;``fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where    F: FnMut(Self::Item) -> Option<B>, `[src]

Creates an iterator that both filters and maps. Read more

#### ⓘImportant traits for Enumerate<I>### Important traits for Enumerate<I> `impl<I> Iterator for Enumerate<I> where    I: Iterator,  type Item = (usize, <I as Iterator>::Item);``fn enumerate(self) -> Enumerate<Self>`[src]

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

#### ⓘImportant traits for Peekable<I>### Important traits for Peekable<I> `impl<I> Iterator for Peekable<I> where    I: Iterator,  type Item = <I as Iterator>::Item;``fn peekable(self) -> Peekable<Self>`[src]

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

#### ⓘImportant traits for SkipWhile<I, P>### Important traits for SkipWhile<I, P> `impl<I, P> Iterator for SkipWhile<I, P> where    I: Iterator,    P: FnMut(&<I as Iterator>::Item) -> bool,  type Item = <I as Iterator>::Item;``fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where    P: FnMut(&Self::Item) -> bool, `[src]

Creates an iterator that [`skip`]s elements based on a predicate. Read more

#### ⓘImportant traits for TakeWhile<I, P>### Important traits for TakeWhile<I, P> `impl<I, P> Iterator for TakeWhile<I, P> where    I: Iterator,    P: FnMut(&<I as Iterator>::Item) -> bool,  type Item = <I as Iterator>::Item;``fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where    P: FnMut(&Self::Item) -> bool, `[src]

Creates an iterator that yields elements based on a predicate. Read more

#### ⓘImportant traits for Skip<I>### Important traits for Skip<I> `impl<I> Iterator for Skip<I> where    I: Iterator,  type Item = <I as Iterator>::Item;``fn skip(self, n: usize) -> Skip<Self>`[src]

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

#### ⓘImportant traits for Take<I>### Important traits for Take<I> `impl<I> Iterator for Take<I> where    I: Iterator,  type Item = <I as Iterator>::Item;``fn take(self, n: usize) -> Take<Self>`[src]

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

#### ⓘImportant traits for Scan<I, St, F>### Important traits for Scan<I, St, F> `impl<B, I, St, F> Iterator for Scan<I, St, F> where    F: FnMut(&mut St, <I as Iterator>::Item) -> Option<B>,    I: Iterator,  type Item = B;``fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where    F: FnMut(&mut St, Self::Item) -> Option<B>, `[src]

An iterator adaptor similar to [`fold`] that holds internal state and produces a new iterator. Read more

#### ⓘImportant traits for FlatMap<I, U, F>### Important traits for FlatMap<I, U, F> `impl<I, U, F> Iterator for FlatMap<I, U, F> where    F: FnMut(<I as Iterator>::Item) -> U,    I: Iterator,    U: IntoIterator,  type Item = <U as IntoIterator>::Item;``fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where    F: FnMut(Self::Item) -> U,    U: IntoIterator, `[src]

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

#### ⓘImportant traits for Flatten<I>### Important traits for Flatten<I> `impl<I, U> Iterator for Flatten<I> where    I: Iterator,    U: Iterator,    <I as Iterator>::Item: IntoIterator,    <<I as Iterator>::Item as IntoIterator>::IntoIter == U,    <<I as Iterator>::Item as IntoIterator>::Item == <U as Iterator>::Item,  type Item = <U as Iterator>::Item;``fn flatten(self) -> Flatten<Self> where    Self::Item: IntoIterator, `[src]

🔬 This is a nightly-only experimental API. (`iterator_flatten `#48213)

Creates an iterator that flattens nested structure. Read more

#### ⓘImportant traits for Fuse<I>### Important traits for Fuse<I> `impl<I> Iterator for Fuse<I> where    I: Iterator,  type Item = <I as Iterator>::Item;impl<I> Iterator for Fuse<I> where    I: FusedIterator, ``fn fuse(self) -> Fuse<Self>`[src]

Creates an iterator which ends after the first [`None`]. Read more

#### ⓘImportant traits for Inspect<I, F>### Important traits for Inspect<I, F> `impl<I, F> Iterator for Inspect<I, F> where    F: FnMut(&<I as Iterator>::Item),    I: Iterator,  type Item = <I as Iterator>::Item;``fn inspect<F>(self, f: F) -> Inspect<Self, F> where    F: FnMut(&Self::Item), `[src]

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

#### ⓘImportant traits for &'a mut I### Important traits for &'a mut I `impl<'a, I> Iterator for &'a mut I where    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W``fn by_ref(&mut self) -> &mut Self`[src]

Borrows an iterator, rather than consuming it. Read more

#### ```#[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] fn collect<B>(self) -> B where    B: FromIterator<Self::Item>, ```[src]

Transforms an iterator into a collection. Read more

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

Consumes an iterator, creating two collections from it. Read more

#### `fn try_for_each<F, R>(&mut self, f: F) -> R where    F: FnMut(Self::Item) -> R,    R: Try<Ok = ()>, `1.27.0[src]

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error. Read more

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

Tests if every element of the iterator matches a predicate. Read more

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

Tests if any element of the iterator matches a predicate. Read more

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

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

#### `fn find_map<B, F>(&mut self, f: F) -> Option<B> where    F: FnMut(Self::Item) -> Option<B>, `[src]

🔬 This is a nightly-only experimental API. (`iterator_find_map `#49602)

unstable new API

Applies function to the elements of iterator and returns the first non-none result. Read more

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

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

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

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

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

Returns the maximum element of an iterator. Read more

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

Returns the minimum element of an iterator. Read more

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

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

#### `fn max_by<F>(self, compare: F) -> Option<Self::Item> where    F: FnMut(&Self::Item, &Self::Item) -> Ordering, `1.15.0[src]

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

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

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

#### `fn min_by<F>(self, compare: F) -> Option<Self::Item> where    F: FnMut(&Self::Item, &Self::Item) -> Ordering, `1.15.0[src]

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

#### ⓘImportant traits for Rev<I>### Important traits for Rev<I> `impl<I> Iterator for Rev<I> where    I: DoubleEndedIterator,  type Item = <I as Iterator>::Item;``fn rev(self) -> Rev<Self> where    Self: DoubleEndedIterator, `[src]

Reverses an iterator's direction. Read more

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

Converts an iterator of pairs into a pair of containers. Read more

#### ⓘImportant traits for Cloned<I>### Important traits for Cloned<I> `impl<'a, I, T> Iterator for Cloned<I> where    I: Iterator<Item = &'a T>,    T: 'a + Clone,  type Item = T;``fn cloned<'a, T>(self) -> Cloned<Self> where    Self: Iterator<Item = &'a T>,    T: 'a + Clone, `[src]

Creates an iterator which [`clone`]s all of its elements. Read more

#### ⓘImportant traits for Cycle<I>### Important traits for Cycle<I> `impl<I> Iterator for Cycle<I> where    I: Clone + Iterator,  type Item = <I as Iterator>::Item;``fn cycle(self) -> Cycle<Self> where    Self: Clone, `[src]

Repeats an iterator endlessly. Read more

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

Sums the elements of an iterator. Read more

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

Iterates over the entire iterator, multiplying all the elements Read more

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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