Struct core::iter::Map

#[must_use = "iterators 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]);

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);
}

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);
}

Trait 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.

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

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

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

fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R where
    Self: Sized,
    G: FnMut(Acc, Self::Item) -> R,
    R: Try<Ok = Acc>, 

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

fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc where
    G: FnMut(Acc, Self::Item) -> Acc, 

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

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

Returns the nth element from the end of the iterator.

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

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

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

fn len(&self) -> usize

Returns the exact length of the iterator.

fn is_empty(&self) -> bool

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

Returns true if the iterator is empty.

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

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 try_fold<Acc, G, R>(&mut self, init: Acc, g: G) -> R where
    Self: Sized,
    G: FnMut(Acc, Self::Item) -> R,
    R: Try<Ok = Acc>, 

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

fn fold<Acc, G>(self, init: Acc, g: G) -> Acc where
    G: FnMut(Acc, Self::Item) -> Acc, 

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

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>

Returns the nth element of the iterator.

fn step_by(self, step: usize) -> StepBy<Self> where
    Self: Sized, 

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

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 for_each<F>(self, f: F) where
    Self: Sized,
    F: FnMut(Self::Item), 

Calls a closure on each element of an iterator.

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 map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> where
    Self: Sized,
    P: FnMut(Self::Item) -> Option<B>, 

🔬 This is a nightly-only experimental API. (iter_map_while #68537)

recently added

Creates an iterator that both yields elements based on a predicate and maps.

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 flatten(self) -> Flatten<Self> where
    Self: Sized,
    Self::Item: IntoIterator, 

Creates an iterator that 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), 

Does 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.

#[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]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 partition_in_place<'a, T: 'a, P>(self, predicate: P) -> usize where
    Self: Sized + DoubleEndedIterator<Item = &'a mut T>,
    P: FnMut(&T) -> bool, 

🔬 This is a nightly-only experimental API. (iter_partition_in_place #62543)

new API

Reorders the elements of this iterator in-place according to the given predicate, such that all those that return true precede all those that return false. Returns the number of true elements found.

fn is_partitioned<P>(self, predicate: P) -> bool where
    Self: Sized,
    P: FnMut(Self::Item) -> bool, 

🔬 This is a nightly-only experimental API. (iter_is_partitioned #62544)

new API

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false.

fn try_for_each<F, R>(&mut self, f: F) -> R where
    Self: Sized,
    F: FnMut(Self::Item) -> R,
    R: Try<Ok = ()>, 

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

fn fold_first<F>(self, f: F) -> Option<Self::Item> where
    Self: Sized,
    F: FnMut(Self::Item, Self::Item) -> Self::Item, 

🔬 This is a nightly-only experimental API. (iterator_fold_self #68125)

The same as fold(), but uses the first element in the iterator as the initial value, folding every subsequent element into it. If the iterator is empty, return None; otherwise, return the result of the fold.

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 find_map<B, F>(&mut self, f: F) -> Option<B> where
    Self: Sized,
    F: FnMut(Self::Item) -> Option<B>, 

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

fn try_find<F, E, R>(&mut self, f: F) -> Result<Option<Self::Item>, E> where
    Self: Sized,
    F: FnMut(&Self::Item) -> R,
    R: Try<Ok = bool, Error = E>, 

🔬 This is a nightly-only experimental API. (try_find #63178)

new API

Applies function to the elements of iterator and returns the first non-none result or the first error.

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

Returns the element that gives the maximum value with respect to the specified comparison 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 min_by<F>(self, compare: F) -> Option<Self::Item> where
    Self: Sized,
    F: FnMut(&Self::Item, &Self::Item) -> Ordering, 

Returns the element that gives the minimum value with respect to the specified comparison 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 copied<'a, T: 'a>(self) -> Copied<Self> where
    Self: Sized + Iterator<Item = &'a T>,
    T: Copy, 

Creates an iterator which copies all of its elements.

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
    Self: Sized,
    S: Sum<Self::Item>, 

Sums the elements of an iterator.

fn product<P>(self) -> P where
    Self: Sized,
    P: Product<Self::Item>, 

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 cmp_by<I, F>(self, other: I, cmp: F) -> Ordering where
    Self: Sized,
    I: IntoIterator,
    F: FnMut(Self::Item, I::Item) -> Ordering, 

🔬 This is a nightly-only experimental API. (iter_order_by #64295)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

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 partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering> where
    Self: Sized,
    I: IntoIterator,
    F: FnMut(Self::Item, I::Item) -> Option<Ordering>, 

🔬 This is a nightly-only experimental API. (iter_order_by #64295)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

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 eq_by<I, F>(self, other: I, eq: F) -> bool where
    Self: Sized,
    I: IntoIterator,
    F: FnMut(Self::Item, I::Item) -> bool, 

🔬 This is a nightly-only experimental API. (iter_order_by #64295)

Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function.

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.

fn is_sorted(self) -> bool where
    Self: Sized,
    Self::Item: PartialOrd, 

🔬 This is a nightly-only experimental API. (is_sorted #53485)

new API

Checks if the elements of this iterator are sorted.

fn is_sorted_by<F>(self, compare: F) -> bool where
    Self: Sized,
    F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>, 

🔬 This is a nightly-only experimental API. (is_sorted #53485)

new API

Checks if the elements of this iterator are sorted using the given comparator function.

fn is_sorted_by_key<F, K>(self, f: F) -> bool where
    Self: Sized,
    F: FnMut(Self::Item) -> K,
    K: PartialOrd, 

🔬 This is a nightly-only experimental API. (is_sorted #53485)

new API

Checks if the elements of this iterator are sorted using the given key extraction function.

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