Struct core::iter::Map

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct Map<I, F> {
    // some 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:

fn main() { let v: Vec<i32> = vec![1, 2, 3].into_iter().rev().map(|x| x + 1).collect(); assert_eq!(v, [4, 3, 2]); }

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

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

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:

fn main() { let mut c = 0; for pair in vec!['a', 'b', 'c'].into_iter() .map(|letter| { c += 1; (letter, c) }) { println!("{:?}", pair); } }

let mut c = 0;

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

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.

fn main() { let mut c = 0; for pair in vec!['a', 'b', 'c'].into_iter() .map(|letter| { c += 1; (letter, c) }) .rev() { println!("{:?}", pair); } }

let mut c = 0;

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

Trait Implementations

impl<I: Debug, F> Debug for Map<I, F>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

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

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.

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

Returns the bounds on the remaining length of the iterator.

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

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

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

Consumes the iterator, returning the last element.

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.

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.

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.

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.

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.

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.

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

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

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.

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.

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.

fn skip(self, n: usize) -> Skip<Self> where Self: Sized

Creates an iterator that skips the first n elements.

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

Creates an iterator that yields its first n elements.

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.

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.

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

Creates an iterator which ends after the first 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.

fn by_ref(&mut self) -> &mut Self where Self: Sized

Borrows an iterator, rather than consuming it.

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

Transforms an iterator into a collection.

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.

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.

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.

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.

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.

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.

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.

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

Returns the maximum element of an iterator.

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

Returns the minimum element of an iterator.

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

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

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

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

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

Reverses an iterator's direction.

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.

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.

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

Repeats an iterator endlessly.

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

Sums the elements of an iterator.

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

Iterates over the entire iterator, multiplying all the elements

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

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

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

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

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

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

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

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

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

impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where F: FnMut(I::Item) -> B

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

An iterator able to yield elements from both ends.

impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F> where F: FnMut(I::Item) -> B

fn len(&self) -> usize

Returns the exact number of times the iterator will iterate.

Derived Implementations

impl<I: Clone, F: Clone> Clone for Map<I, F>

fn clone(&self) -> Map<I, F>

Returns a copy of the value.

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

Performs copy-assignment from source.