Trait nom::lib::std::prelude::v1::v1::DoubleEndedIterator 1.0.0
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pub trait DoubleEndedIterator: Iterator { fn next_back(&mut self) -> Option<Self::Item>; fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>, { ... } fn rfold<B, F>(self, accum: B, f: F) -> B
where
F: FnMut(B, Self::Item) -> B, { ... } 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
interchangeable 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 try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)This is the reverse version of try_fold()
: it takes elements
starting from the back of the iterator.
Examples
Basic usage:
#![feature(iterator_try_fold)] let a = ["1", "2", "3"]; let sum = a.iter() .map(|&s| s.parse::<i32>()) .try_rfold(0, |acc, x| x.and_then(|y| Ok(acc + y))); assert_eq!(sum, Ok(6));
Short-circuiting:
#![feature(iterator_try_fold)] let a = ["1", "rust", "3"]; let mut it = a.iter(); let sum = it .by_ref() .map(|&s| s.parse::<i32>()) .try_rfold(0, |acc, x| x.and_then(|y| Ok(acc + y))); assert!(sum.is_err()); // Because it short-circuited, the remaining elements are still // available through the iterator. assert_eq!(it.next_back(), Some(&"1"));
fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
F: FnMut(B, Self::Item) -> B,
iter_rfold
)An iterator method that reduces the iterator's elements to a single, final value, starting from the back.
This is the reverse version of fold()
: it takes elements starting from
the back of the iterator.
rfold()
takes two arguments: an initial value, and a closure with two
arguments: an 'accumulator', and an element. The closure returns the value that
the accumulator should have for the next iteration.
The initial value is the value the accumulator will have on the first call.
After applying this closure to every element of the iterator, rfold()
returns the accumulator.
This operation is sometimes called 'reduce' or 'inject'.
Folding is useful whenever you have a collection of something, and want to produce a single value from it.
Examples
Basic usage:
#![feature(iter_rfold)] let a = [1, 2, 3]; // the sum of all of the elements of a let sum = a.iter() .rfold(0, |acc, &x| acc + x); assert_eq!(sum, 6);
This example builds a string, starting with an initial value and continuing with each element from the back until the front:
#![feature(iter_rfold)] let numbers = [1, 2, 3, 4, 5]; let zero = "0".to_string(); let result = numbers.iter().rfold(zero, |acc, &x| { format!("({} + {})", x, acc) }); assert_eq!(result, "(1 + (2 + (3 + (4 + (5 + 0)))))");
fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
P: FnMut(&Self::Item) -> bool,
iter_rfind
)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));
Implementations on Foreign Types
impl<'a> DoubleEndedIterator for Components<'a>
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fn next_back(&mut self) -> Option<Component<'a>>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)impl DoubleEndedIterator for Args
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fn next_back(&mut self) -> Option<String>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)impl DoubleEndedIterator for ArgsOs
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fn next_back(&mut self) -> Option<OsString>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)impl<'a> DoubleEndedIterator for Iter<'a>
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fn next_back(&mut self) -> Option<&'a OsStr>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)impl<'a, I> DoubleEndedIterator for &'a mut I where
I: DoubleEndedIterator + ?Sized,
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I: DoubleEndedIterator + ?Sized,
fn next_back(&mut self) -> Option<<I as Iterator>::Item>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)impl DoubleEndedIterator for EscapeDefault
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fn next_back(&mut self) -> Option<u8>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)impl<'a> DoubleEndedIterator for Memchr<'a>
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fn next_back(&mut self) -> Option<<Memchr<'a> as Iterator>::Item>
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fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
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F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,
iterator_try_fold
)fn rfold<B, F>(self, accum: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
iter_rfold
)fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,
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P: FnMut(&Self::Item) -> bool,
iter_rfind
)Implementors
impl<'a, T> DoubleEndedIterator for ExactChunks<'a, T>
impl<'a, P> DoubleEndedIterator for SplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<T> DoubleEndedIterator for Once<T>
impl<'a, T, P> DoubleEndedIterator for SplitMut<'a, T, P> where
P: FnMut(&T) -> bool,impl<I, F> DoubleEndedIterator for Inspect<I, F> where
F: FnMut(&<I as Iterator>::Item),
I: DoubleEndedIterator,impl<T> DoubleEndedIterator for nom::lib::std::result::IntoIter<T>
impl<'a, I, T> DoubleEndedIterator for Cloned<I> where
I: DoubleEndedIterator<Item = &'a T>,
T: 'a + Clone,impl<B, I, F> DoubleEndedIterator for FilterMap<I, F> where
F: FnMut(<I as Iterator>::Item) -> Option<B>,
I: DoubleEndedIterator,impl<A, B> DoubleEndedIterator for Chain<A, B> where
A: DoubleEndedIterator,
B: DoubleEndedIterator<Item = <A as Iterator>::Item>,impl<I> DoubleEndedIterator for Rev<I> where
I: DoubleEndedIterator,impl<'a, P> DoubleEndedIterator for RMatches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, T> DoubleEndedIterator for nom::lib::std::result::Iter<'a, T>
impl<'a, P> DoubleEndedIterator for nom::lib::std::str::RSplit<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, T, P> DoubleEndedIterator for nom::lib::std::slice::RSplit<'a, T, P> where
P: FnMut(&T) -> bool,impl<T> DoubleEndedIterator for Empty<T>
impl<'a> DoubleEndedIterator for Lines<'a>
impl<'a, P> DoubleEndedIterator for MatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a> DoubleEndedIterator for LinesAny<'a>
impl<I, P> DoubleEndedIterator for Filter<I, P> where
I: DoubleEndedIterator,
P: FnMut(&<I as Iterator>::Item) -> bool,impl<'a, P> DoubleEndedIterator for nom::lib::std::str::Split<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a> DoubleEndedIterator for Bytes<'a>
impl<I, U> DoubleEndedIterator for Flatten<I> where
I: DoubleEndedIterator,
U: DoubleEndedIterator,
<I as Iterator>::Item: IntoIterator,
<<I as Iterator>::Item as IntoIterator>::IntoIter == U,
<<I as Iterator>::Item as IntoIterator>::Item == <U as Iterator>::Item,impl<B, I, F> DoubleEndedIterator for Map<I, F> where
F: FnMut(<I as Iterator>::Item) -> B,
I: DoubleEndedIterator,impl<'a, T> DoubleEndedIterator for nom::lib::std::result::IterMut<'a, T>
impl<A, F> DoubleEndedIterator for RepeatWith<F> where
F: FnMut() -> A,impl<'a> DoubleEndedIterator for Chars<'a>
impl<I> DoubleEndedIterator for Fuse<I> where
I: DoubleEndedIterator,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 Enumerate<I> where
I: ExactSizeIterator + DoubleEndedIterator,impl<'a, T> DoubleEndedIterator for ExactChunksMut<'a, T>
impl<A> DoubleEndedIterator for Repeat<A> where
A: Clone,impl<'a, T> DoubleEndedIterator for nom::lib::std::slice::IterMut<'a, T>
impl<A> DoubleEndedIterator for RangeInclusive<A> where
A: Step,impl<A, B> DoubleEndedIterator for Zip<A, B> where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,impl<A> DoubleEndedIterator for nom::lib::std::option::IntoIter<A>
impl<'a, P> DoubleEndedIterator for RMatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, T> DoubleEndedIterator for nom::lib::std::slice::Iter<'a, T>
impl<A> DoubleEndedIterator for nom::lib::std::ops::Range<A> where
A: Step,impl<'a, T> DoubleEndedIterator for Chunks<'a, T>
impl<I> DoubleEndedIterator for Skip<I> where
I: DoubleEndedIterator + ExactSizeIterator,impl<'a> DoubleEndedIterator for CharIndices<'a>
impl<'a, T, P> DoubleEndedIterator for nom::lib::std::slice::Split<'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 ChunksMut<'a, T>
impl<'a, A> DoubleEndedIterator for nom::lib::std::option::Iter<'a, A>
impl<I> DoubleEndedIterator for Fuse<I> where
I: DoubleEndedIterator + FusedIterator,impl<'a, A> DoubleEndedIterator for nom::lib::std::option::IterMut<'a, A>
impl<'a, P> DoubleEndedIterator for Matches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<'a, T> DoubleEndedIterator for Windows<'a, T>
impl<'a, P> DoubleEndedIterator for RSplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,impl<T> DoubleEndedIterator for nom::lib::std::vec::IntoIter<T>
impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V>
impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::btree_set::Range<'a, T>
impl<'a, K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::Iter<'a, K, V> where
K: 'a,
V: 'a,impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V>
impl<'a, K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::Range<'a, K, V>
impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::linked_list::Iter<'a, T>
impl<I> DoubleEndedIterator for Box<I> where
I: DoubleEndedIterator + ?Sized,impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::btree_set::Iter<'a, T>
impl<'a, I> DoubleEndedIterator for Splice<'a, I> where
I: Iterator,impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::binary_heap::Iter<'a, T>
impl<'a, K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::IterMut<'a, K, V> where
K: 'a,
V: 'a,impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::linked_list::IterMut<'a, T>
impl<'a, T> DoubleEndedIterator for nom::lib::std::vec::Drain<'a, T>
impl<T> DoubleEndedIterator for nom::lib::std::collections::linked_list::IntoIter<T>
impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::Iter<'a, T>
impl<K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::IntoIter<K, V>
impl<'a> DoubleEndedIterator for nom::lib::std::string::Drain<'a>
impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::binary_heap::Drain<'a, T> where
T: 'a,impl<T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::IntoIter<T>
impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::Drain<'a, T> where
T: 'a,impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::IterMut<'a, T>
impl<T> DoubleEndedIterator for nom::lib::std::collections::btree_set::IntoIter<T>
impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V>
impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V>
impl<T> DoubleEndedIterator for nom::lib::std::collections::binary_heap::IntoIter<T>
impl<'a> DoubleEndedIterator for SplitWhitespace<'a>