Struct std::iter::Map

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

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

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

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fn clone(&self) -> Map<I, F> ⓘ

Returns a copy of the value. Read more

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

Performs copy-assignment from source. Read more

1.9.0source

impl<I, F> Debug for Map<I, F>
where
    I: Debug,

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

Formats the value using the given formatter. Read more

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

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

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

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fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R
where
    Map<I, F>: Sized,
    G: FnMut(Acc, <Map<I, F> as Iterator>::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. Read more

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

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

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fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize>

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

Advances the iterator from the back by n elements. Read more

1.37.0source

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

Returns the nth element from the end of the iterator. Read more

1.27.0source

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. Read more

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

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fn len(&self) -> usize

Returns the exact remaining length of the iterator. Read more

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fn is_empty(&self) -> bool

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

Returns true if the iterator is empty. Read more

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

type Item = B

The type of the elements being iterated over.

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

Advances the iterator and returns the next value. Read more

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

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

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

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

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

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

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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)

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

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

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

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

Consumes the iterator, returning the last element. Read more

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

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

Advances the iterator by n elements. Read more

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

Returns the nth element of the iterator. Read more

1.28.0source

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. Read more

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fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> ⓘ
where
    Self: Sized,
    U: IntoIterator<Item = Self::Item>,

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

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fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> ⓘ
where
    Self: Sized,
    U: IntoIterator,

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

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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)

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

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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. Read more

1.21.0source

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

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

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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. Read more

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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. Read more

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

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

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fn peekable(self) -> Peekable<Self> ⓘ
where
    Self: Sized,

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. Read more

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fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
where
    Self: Sized,
    P: FnMut(&Self::Item) -> bool,

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

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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. Read more

1.57.0source

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

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

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

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

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

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

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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 adapter which, like fold, holds internal state, but unlike fold, produces a new iterator. Read more

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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. Read more

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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)

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. Read more

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

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

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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. Read more

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

Borrows an iterator, rather than consuming it. Read more

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

Transforms an iterator into a collection. Read more

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

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

Collects all the items from an iterator into a collection. Read more

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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. Read more

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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)

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. Read more

1.27.0source

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

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

1.51.0source

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

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

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fn try_reduce<F, R>(
    &mut self,
    f: F
) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
where
    Self: Sized,
    F: FnMut(Self::Item, Self::Item) -> R,
    R: Try<Output = Self::Item>,
    <R as Try>::Residual: Residual<Option<Self::Item>>,

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

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. Read more

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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. Read more

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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. Read more

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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. Read more

1.30.0source

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. Read more

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fn try_find<F, R>(
    &mut self,
    f: F
) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
where
    Self: Sized,
    F: FnMut(&Self::Item) -> R,
    R: Try<Output = bool>,
    <R as Try>::Residual: Residual<Option<Self::Item>>,

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

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

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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. Read more

1.6.0source

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

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

1.15.0source

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. Read more

1.6.0source

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

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

1.15.0source

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. Read more

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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. Read more

1.36.0source

fn copied<'a, T>(self) -> Copied<Self> ⓘ
where
    T: 'a + Copy,
    Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which copies all of its elements. Read more

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fn cloned<'a, T>(self) -> Cloned<Self> ⓘ
where
    T: 'a + Clone,
    Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which clones all of its elements. Read more

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

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

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

1.11.0source

fn sum<S>(self) -> S
where
    Self: Sized,
    S: Sum<Self::Item>,

Sums the elements of an iterator. Read more

1.11.0source

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

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

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

1.5.0source

fn partial_cmp<I>(self, other: I) -> Option<Ordering>
where
    I: IntoIterator,
    Self::Item: PartialOrd<<I as IntoIterator>::Item>,
    Self: Sized,

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. Read more

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

1.5.0source

fn eq<I>(self, other: I) -> bool
where
    I: IntoIterator,
    Self::Item: PartialEq<<I as IntoIterator>::Item>,
    Self: Sized,

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

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

1.5.0source

fn ne<I>(self, other: I) -> bool
where
    I: IntoIterator,
    Self::Item: PartialEq<<I as IntoIterator>::Item>,
    Self: Sized,

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

1.5.0source

fn lt<I>(self, other: I) -> bool
where
    I: IntoIterator,
    Self::Item: PartialOrd<<I as IntoIterator>::Item>,
    Self: Sized,

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

1.5.0source

fn le<I>(self, other: I) -> bool
where
    I: IntoIterator,
    Self::Item: PartialOrd<<I as IntoIterator>::Item>,
    Self: Sized,

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

1.5.0source

fn gt<I>(self, other: I) -> bool
where
    I: IntoIterator,
    Self::Item: PartialOrd<<I as IntoIterator>::Item>,
    Self: Sized,

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

1.5.0source

fn ge<I>(self, other: I) -> bool
where
    I: IntoIterator,
    Self::Item: PartialOrd<<I as IntoIterator>::Item>,
    Self: Sized,

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

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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)

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

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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)

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

1.26.0source

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

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

Auto Trait Implementations

impl<I, F> RefUnwindSafe for Map<I, F>
where
    F: RefUnwindSafe,
    I: RefUnwindSafe,

impl<I, F> Send for Map<I, F>
where
    F: Send,
    I: Send,

impl<I, F> Sync for Map<I, F>
where
    F: Sync,
    I: Sync,

impl<I, F> Unpin for Map<I, F>
where
    F: Unpin,
    I: Unpin,

impl<I, F> UnwindSafe for Map<I, F>
where
    F: UnwindSafe,
    I: UnwindSafe,

Blanket Implementations

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impl<T> Any for T
where
    T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more

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impl<T> Borrow<T> for T
where
    T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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impl<T> BorrowMut<T> for T
where
    T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where
    U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<I> IntoIterator for I
where
    I: Iterator,

type Item = <I as Iterator>::Item

The type of the elements being iterated over.

type IntoIter = I

Which kind of iterator are we turning this into?

const: unstablesource

fn into_iter(self) -> I

Creates an iterator from a value. Read more

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impl<T> ToOwned for T
where
    T: Clone,

type Owned = T

The resulting type after obtaining ownership.

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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more

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impl<T, U> TryFrom<U> for T
where
    U: Into<T>,

type Error = Infallible

The type returned in the event of a conversion error.

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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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impl<T, U> TryInto<U> for T
where
    U: TryFrom<T>,

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/iter/struct.Map.html

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Struct std::iter::Map

Notes about side effects

Trait Implementations

Auto Trait Implementations

Blanket Implementations