Struct Map 

pub struct Map<I, F> { /* private fields */ }

Available on non-crate feature ferrocene_certified only.

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> = [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 ['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 ['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 duplicate of the value.

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

where 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<Output = Acc>,

This is the reverse version of Iterator::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 advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>>

🔬This is a nightly-only experimental API. (iter_advance_by #77404)

Advances the iterator from the back by n elements.

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 remaining 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: 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<Output = Acc>,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

Folds every element into an accumulator by applying an operation, returning the final result.

fn next_chunk<const N: usize>( &mut self, ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_next_chunk #98326)

Available on non-crate feature ferrocene_certified only.

Advances the iterator and returns an array containing the next N values.

fn count(self) -> usize

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

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

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

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

Consumes the iterator, returning the last element.

fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>

🔬This is a nightly-only experimental API. (iter_advance_by #77404)

Available on non-crate feature ferrocene_certified only.

Advances the iterator by n elements.

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

Available on non-crate feature ferrocene_certified only.

Returns the nth element of the iterator.

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

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

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>,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

‘Zips up’ two iterators into a single iterator of pairs.

fn intersperse(self, separator: Self::Item) -> Intersperse<Self>

where Self: Sized, Self::Item: Clone,

🔬This is a nightly-only experimental API. (iter_intersperse #79524)

Available on non-crate feature ferrocene_certified only.

Creates a new iterator which places a copy of separator between adjacent items of the original iterator.

fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>

where Self: Sized, G: FnMut() -> Self::Item,

🔬This is a nightly-only experimental API. (iter_intersperse #79524)

Available on non-crate feature ferrocene_certified only.

Creates a new iterator which places an item generated by separator between adjacent items of the original iterator.

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),

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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>,

Available on non-crate feature ferrocene_certified only.

Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate<Self>

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

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

fn peekable(self) -> Peekable<Self>

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

Creates an iterator which can use the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information.

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

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Available on non-crate feature ferrocene_certified only.

Creates an iterator that skips elements based on a predicate.

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

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Available on non-crate feature ferrocene_certified only.

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>,

Available on non-crate feature ferrocene_certified only.

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

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

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

Creates an iterator that skips the first n elements.

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

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner.

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>,

Available on non-crate feature ferrocene_certified only.

An iterator adapter which, like fold, holds internal state, but unlike fold, 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,

Available on non-crate feature ferrocene_certified only.

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

fn flatten(self) -> Flatten<Self>

where Self: Sized, Self::Item: IntoIterator,

Available on non-crate feature ferrocene_certified only.

Creates an iterator that flattens nested structure.

fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N>

where Self: Sized, F: FnMut(&[Self::Item; N]) -> R,

🔬This is a nightly-only experimental API. (iter_map_windows #87155)

Available on non-crate feature ferrocene_certified only.

Calls the given function f for each contiguous window of size N over self and returns an iterator over the outputs of f. Like slice::windows(), the windows during mapping overlap as well.

fn fuse(self) -> Fuse<Self>

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

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),

Available on non-crate feature ferrocene_certified only.

Does something with each element of an iterator, passing the value on.

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

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

Creates a “by reference” adapter for this instance of Iterator.

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

where Self: Sized,

Available on non-crate feature ferrocene_certified only.

Transforms an iterator into a collection.

fn try_collect<B>(&mut self) -> <Self::Item::Residual as Residual<B>>::TryType

where Self: Sized, Self::Item: Try<Residual: Residual<B>>, B: FromIterator<<Self::Item as Try>::Output>,

🔬This is a nightly-only experimental API. (iterator_try_collect #94047)

Available on non-crate feature ferrocene_certified only.

Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered.

fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut E

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_collect_into #94780)

Available on non-crate feature ferrocene_certified only.

Collects all the items from 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,

Available on non-crate feature ferrocene_certified only.

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)

Available on non-crate feature ferrocene_certified only.

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)

Available on non-crate feature ferrocene_certified only.

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<Output = ()>,

Available on non-crate feature ferrocene_certified only.

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

fn reduce<F>(self, f: F) -> Option<Self::Item>

where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item,

Available on non-crate feature ferrocene_certified only.

Reduces the elements to a single one, by repeatedly applying a reducing operation.

fn try_reduce<R>( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <R::Residual as Residual<Option<R::Output>>>::TryType

where Self: Sized, R: Try<Output = Self::Item, Residual: Residual<Option<Self::Item>>>,

🔬This is a nightly-only experimental API. (iterator_try_reduce #87053)

Available on non-crate feature ferrocene_certified only.

Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately.

fn all<F>(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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>,

Available on non-crate feature ferrocene_certified only.

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

fn try_find<R>( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <R::Residual as Residual<Option<Self::Item>>>::TryType

where Self: Sized, R: Try<Output = bool, Residual: Residual<Option<Self::Item>>>,

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

Available on non-crate feature ferrocene_certified only.

Applies function to the elements of iterator and returns the first true result or the first error.

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

where Self: Sized, P: FnMut(Self::Item) -> bool,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

Returns the maximum element of an iterator.

fn min(self) -> Option<Self::Item>

where Self: Sized, Self::Item: Ord,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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

fn rev(self) -> Rev<Self>

where Self: Sized + DoubleEndedIterator,

Available on non-crate feature ferrocene_certified only.

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)>,

Available on non-crate feature ferrocene_certified only.

Converts an iterator of pairs into a pair of containers.

fn copied<'a, T>(self) -> Copied<Self>

where T: Copy + 'a, Self: Sized + Iterator<Item = &'a T>,

Available on non-crate feature ferrocene_certified only.

Creates an iterator which copies all of its elements.

fn cloned<'a, T>(self) -> Cloned<Self>

where T: Clone + 'a, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which clones all of its elements.

fn cycle(self) -> Cycle<Self>

where Self: Sized + Clone,

Available on non-crate feature ferrocene_certified only.

Repeats an iterator endlessly.

fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>

where Self: Sized,

🔬This is a nightly-only experimental API. (iter_array_chunks #100450)

Available on non-crate feature ferrocene_certified only.

Returns an iterator over N elements of the iterator at a time.

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>,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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)

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

Lexicographically compares the PartialOrd elements of this Iterator with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned.

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)

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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)

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

Determines if the elements of this Iterator are not equal to those of another.

fn lt<I>(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<I::Item>, Self: Sized,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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) -> bool,

Available on non-crate feature ferrocene_certified only.

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,

Available on non-crate feature ferrocene_certified only.

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

impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>

where F: FnMut(I::Item) -> B,

impl<B, I, F> TrustedLen for Map<I, F>

where I: TrustedLen, F: FnMut(I::Item) -> B,