std::iter::DoubleEndedIterator
Trait std::iter::DoubleEndedIterator
pub trait DoubleEndedIterator: Iterator { fn next_back(&mut self) -> Option<Self::Item>; fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool, { ... } }
An iterator able to yield elements from both ends.
Something that implements DoubleEndedIterator
has one extra capability over something that implements Iterator
: the ability to also take Item
s from the back, as well as the front.
It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle.
In a similar fashion to the Iterator
protocol, once a DoubleEndedIterator
returns None
from a next_back()
, calling it again may or may not ever return Some
again. next()
and next_back()
are interchangable for this purpose.
Examples
Basic usage:
let numbers = vec![1, 2, 3, 4, 5, 6]; let mut iter = numbers.iter(); assert_eq!(Some(&1), iter.next()); assert_eq!(Some(&6), iter.next_back()); assert_eq!(Some(&5), iter.next_back()); assert_eq!(Some(&2), iter.next()); assert_eq!(Some(&3), iter.next()); assert_eq!(Some(&4), iter.next()); assert_eq!(None, iter.next()); assert_eq!(None, iter.next_back());
Required Methods
fn next_back(&mut self) -> Option<Self::Item>
Removes and returns an element from the end of the iterator.
Returns None
when there are no more elements.
The trait-level docs contain more details.
Examples
Basic usage:
let numbers = vec![1, 2, 3, 4, 5, 6]; let mut iter = numbers.iter(); assert_eq!(Some(&1), iter.next()); assert_eq!(Some(&6), iter.next_back()); assert_eq!(Some(&5), iter.next_back()); assert_eq!(Some(&2), iter.next()); assert_eq!(Some(&3), iter.next()); assert_eq!(Some(&4), iter.next()); assert_eq!(None, iter.next()); assert_eq!(None, iter.next_back());
Provided Methods
fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
P: FnMut(&Self::Item) -> bool,
Searches for an element of an iterator from the right that satisfies a predicate.
rfind()
takes a closure that returns true
or false
. It applies this closure to each element of the iterator, starting at the end, and if any of them return true
, then rfind()
returns Some(element)
. If they all return false
, it returns None
.
rfind()
is short-circuiting; in other words, it will stop processing as soon as the closure returns true
.
Because rfind()
takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation where the argument is a double reference. You can see this effect in the examples below, with &&x
.
Examples
Basic usage:
#![feature(iter_rfind)] let a = [1, 2, 3]; assert_eq!(a.iter().rfind(|&&x| x == 2), Some(&2)); assert_eq!(a.iter().rfind(|&&x| x == 5), None);
Stopping at the first true
:
#![feature(iter_rfind)] let a = [1, 2, 3]; let mut iter = a.iter(); assert_eq!(iter.rfind(|&&x| x == 2), Some(&2)); // we can still use `iter`, as there are more elements. assert_eq!(iter.next_back(), Some(&1));
Implementors
impl<'a, T> DoubleEndedIterator for std::collections::binary_heap::Iter<'a, T>
impl<T> DoubleEndedIterator for std::collections::binary_heap::IntoIter<T>
impl<'a, T> DoubleEndedIterator for std::collections::binary_heap::Drain<'a, T> where
T: 'a,impl<'a, K, V> DoubleEndedIterator for std::collections::btree_map::Iter<'a, K, V> where
K: 'a,
V: 'a,impl<'a, K, V> DoubleEndedIterator for std::collections::btree_map::IterMut<'a, K, V> where
K: 'a,
V: 'a,impl<K, V> DoubleEndedIterator for std::collections::btree_map::IntoIter<K, V>
impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V>
impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V>
impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V>
impl<'a, K, V> DoubleEndedIterator for std::collections::btree_map::Range<'a, K, V>
impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V>
impl<'a, T> DoubleEndedIterator for std::collections::btree_set::Iter<'a, T>
impl<T> DoubleEndedIterator for std::collections::btree_set::IntoIter<T>
impl<'a, T> DoubleEndedIterator for std::collections::btree_set::Range<'a, T>
impl<'a, T> DoubleEndedIterator for std::collections::linked_list::Iter<'a, T>
impl<'a, T> DoubleEndedIterator for std::collections::linked_list::IterMut<'a, T>
impl<T> DoubleEndedIterator for std::collections::linked_list::IntoIter<T>
impl<'a> DoubleEndedIterator for std::string::Drain<'a>
impl<T> DoubleEndedIterator for std::vec::IntoIter<T>
impl<'a, T> DoubleEndedIterator for std::vec::Drain<'a, T>
impl<'a, T> DoubleEndedIterator for std::collections::vec_deque::Iter<'a, T>
impl<'a, T> DoubleEndedIterator for std::collections::vec_deque::IterMut<'a, T>
impl<T> DoubleEndedIterator for std::collections::vec_deque::IntoIter<T>
impl<'a, T> DoubleEndedIterator for std::collections::vec_deque::Drain<'a, T> where
T: 'a,impl<I> DoubleEndedIterator for Box<I> where
I: DoubleEndedIterator + ?Sized,impl<A> DoubleEndedIterator for std::ops::Range<A> where
A: Step + Clone,
&'a A: Add<&'a A>,
&'a A: Sub<&'a A>,
<&'a A as Add<&'a A>>::Output == A,
<&'a A as Sub<&'a A>>::Output == A,impl<A> DoubleEndedIterator for RangeInclusive<A> where
A: Step,
&'a A: Add<&'a A>,
&'a A: Sub<&'a A>,
<&'a A as Add<&'a A>>::Output == A,
<&'a A as Sub<&'a A>>::Output == A,impl<A> DoubleEndedIterator for Repeat<A> where
A: Clone,impl<T> DoubleEndedIterator for Empty<T>
impl<T> DoubleEndedIterator for Once<T>
impl<'a, I> DoubleEndedIterator for &'a mut I where
I: DoubleEndedIterator + ?Sized,impl<I> DoubleEndedIterator for Rev<I> where
I: DoubleEndedIterator,impl<'a, I, T> DoubleEndedIterator for Cloned<I> where
I: DoubleEndedIterator<Item = &'a T>,
T: 'a + Clone,impl<A, B> DoubleEndedIterator for Chain<A, B> where
A: DoubleEndedIterator,
B: DoubleEndedIterator<Item = <A as Iterator>::Item>,impl<A, B> DoubleEndedIterator for Zip<A, B> where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,impl<B, I, F> DoubleEndedIterator for Map<I, F> where
F: FnMut(<I as Iterator>::Item) -> B,
I: DoubleEndedIterator,impl<I, P> DoubleEndedIterator for Filter<I, P> where
I: DoubleEndedIterator,
P: FnMut(&<I as Iterator>::Item) -> bool,impl<B, I, F> DoubleEndedIterator for FilterMap<I, F> where
F: FnMut(<I as Iterator>::Item) -> Option<B>,
I: DoubleEndedIterator,impl<I> DoubleEndedIterator for Enumerate<I> where
I: ExactSizeIterator + DoubleEndedIterator,impl<I> DoubleEndedIterator for Skip<I> where
I: DoubleEndedIterator + ExactSizeIterator,impl<I, U, F> DoubleEndedIterator for FlatMap<I, U, F> where
F: FnMut(<I as Iterator>::Item) -> U,
I: DoubleEndedIterator,
U: IntoIterator,
<U as IntoIterator>::IntoIter: DoubleEndedIterator,impl<I> DoubleEndedIterator for Fuse<I> where
I: DoubleEndedIterator,impl<I> DoubleEndedIterator for Fuse<I> where
I: DoubleEndedIterator + FusedIterator,impl<I, F> DoubleEndedIterator for Inspect<I, F> where
F: FnMut(&<I as Iterator>::Item) -> (),
I: DoubleEndedIterator,impl<'a, A> DoubleEndedIterator for std::option::Iter<'a, A>
impl<'a, A> DoubleEndedIterator for std::option::IterMut<'a, A>
impl<A> DoubleEndedIterator for std::option::IntoIter<A>
impl<'a, T> DoubleEndedIterator for std::result::Iter<'a, T>
impl<'a, T> DoubleEndedIterator for std::result::IterMut<'a, T>
impl<T> DoubleEndedIterator for std::result::IntoIter<T>
impl<'a, T, P> DoubleEndedIterator for std::slice::Split<'a, T, P> where
P: FnMut(&T) -> bool,impl<'a, T, P> DoubleEndedIterator for SplitMut<'a, T, P> where
P: FnMut(&T) -> bool,impl<'a, T, P> DoubleEndedIterator for std::slice::RSplit<'a, T, P> where
P: FnMut(&T) -> bool,impl<'a, T, P> DoubleEndedIterator for RSplitMut<'a, T, P> where
P: FnMut(&T) -> bool,impl<'a, T> DoubleEndedIterator for Windows<'a, T>
impl<'a, T> DoubleEndedIterator for Chunks<'a, T>
impl<'a, T> DoubleEndedIterator for ChunksMut<'a, T>
impl<'a> DoubleEndedIterator for Chars<'a>
impl<'a> DoubleEndedIterator for CharIndices<'a>
impl<'a> DoubleEndedIterator for Bytes<'a>
impl<'a> DoubleEndedIterator for Lines<'a>
impl<'a> DoubleEndedIterator for LinesAny<'a>
impl<'a, T> DoubleEndedIterator for std::slice::Iter<'a, T>
impl<'a, T> DoubleEndedIterator for std::slice::IterMut<'a, T>
impl<'a, P> DoubleEndedIterator for std::str::Split<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for std::str::RSplit<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for SplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for RSplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for MatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for RMatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for Matches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, P> DoubleEndedIterator for RMatches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a> DoubleEndedIterator for SplitWhitespace<'a>
impl DoubleEndedIterator for EscapeDefault
impl DoubleEndedIterator for Args
impl DoubleEndedIterator for ArgsOs
impl<'a> DoubleEndedIterator for std::path::Iter<'a>
impl<'a> DoubleEndedIterator for Components<'a>
© 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/trait.DoubleEndedIterator.html