# Struct std::iter::Map 1.0.0 [−] [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.

# Notes about side effects

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

#### `fn clone(&self) -> Map<I, F>`

Returns a copy of the value. Read more

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

Performs copy-assignment from `source`. Read more

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

#### `fn len(&self) -> usize`

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

#### `fn is_empty(&self) -> bool`

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

Returns whether the iterator is empty. Read more

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

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

#### `type Item = B`

The type of the elements being iterated over.

#### `fn next(&mut self) -> Option<B>`

Advances the iterator and returns the next value. Read more

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

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

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

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

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

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

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

Consumes the iterator, returning the last element. Read more

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

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

#### `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. Read more

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

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

#### `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. Read more

#### `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. Read more

#### `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. Read more

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

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

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

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

#### `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. Read more

#### `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. Read more

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

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

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

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

#### `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. Read more

#### `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. Read more

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

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

#### `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. Read more

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

Borrows an iterator, rather than consuming it. Read more

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

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`

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

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

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`

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`

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

#### `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. Read more

#### `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. Read more

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

Returns the maximum element of an iterator. Read more

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

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

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

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

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

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

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

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)>`

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

#### `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. Read more

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

Repeats an iterator endlessly. Read more

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

Sums the elements of an iterator. Read more

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

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

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::Item>`
1.5.0

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::Item>`
1.5.0

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::Item>`
1.5.0

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::Item>`
1.5.0

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::Item>`
1.5.0

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::Item>`
1.5.0

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::Item>`
1.5.0

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

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

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

Formats the value using the given formatter.

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

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

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

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

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