1.0.0[][src]Trait nom::lib::std::iter::DoubleEndedIterator

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 Items 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

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

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

Examples

Basic usage:

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:

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"));

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:

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:

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)))))");

Searches for an element of an iterator from the back 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:

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:

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 DoubleEndedIterator for Args
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impl<'a> DoubleEndedIterator for Components<'a>
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impl DoubleEndedIterator for ArgsOs
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impl<'a> DoubleEndedIterator for Iter<'a>
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impl<'a, I> DoubleEndedIterator for &'a mut I where
    I: DoubleEndedIterator + ?Sized
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impl DoubleEndedIterator for EscapeDefault
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impl<'a> DoubleEndedIterator for Memchr<'a>
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impl<'a> DoubleEndedIterator for Memchr3<'a>
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impl<'a> DoubleEndedIterator for Memchr2<'a>
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Implementors

impl<'a> DoubleEndedIterator for SplitAsciiWhitespace<'a>
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impl<'a> DoubleEndedIterator for Chars<'a>
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impl<'a> DoubleEndedIterator for Bytes<'a>
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impl<'a> DoubleEndedIterator for CharIndices<'a>
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impl<'a> DoubleEndedIterator for SplitWhitespace<'a>
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impl<'a> DoubleEndedIterator for LinesAny<'a>
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impl<'a> DoubleEndedIterator for Lines<'a>
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impl<'a> DoubleEndedIterator for nom::lib::std::string::Drain<'a>
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impl<'a, A> DoubleEndedIterator for nom::lib::std::option::IterMut<'a, A>
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impl<'a, A> DoubleEndedIterator for nom::lib::std::option::Iter<'a, A>
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impl<'a, I> DoubleEndedIterator for Splice<'a, I> where
    I: Iterator
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impl<'a, I, T> DoubleEndedIterator for Cloned<I> where
    I: DoubleEndedIterator<Item = &'a T>,
    T: 'a + Clone
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impl<'a, K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::Range<'a, K, V>
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impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V>
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impl<'a, K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::IterMut<'a, K, V> where
    K: 'a,
    V: 'a, 
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impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V>
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impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V>
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impl<'a, K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::Iter<'a, K, V> where
    K: 'a,
    V: 'a, 
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impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V>
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impl<'a, P> DoubleEndedIterator for nom::lib::std::str::RSplit<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, P> DoubleEndedIterator for nom::lib::std::str::Split<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
[src]

impl<'a, P> DoubleEndedIterator for SplitTerminator<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, P> DoubleEndedIterator for MatchIndices<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, P> DoubleEndedIterator for RMatchIndices<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, P> DoubleEndedIterator for Matches<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, P> DoubleEndedIterator for RMatches<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, P> DoubleEndedIterator for RSplitTerminator<'a, P> where
    P: Pattern<'a>,
    <P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>, 
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impl<'a, T> DoubleEndedIterator for Windows<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::result::Iter<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::slice::IterMut<'a, T>
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impl<'a, T> DoubleEndedIterator for ExactChunks<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::slice::Iter<'a, T>
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impl<'a, T> DoubleEndedIterator for Chunks<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::result::IterMut<'a, T>
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impl<'a, T> DoubleEndedIterator for ExactChunksMut<'a, T>
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impl<'a, T> DoubleEndedIterator for ChunksMut<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::btree_set::Range<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::binary_heap::Iter<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::linked_list::IterMut<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::binary_heap::Drain<'a, T> where
    T: 'a, 
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impl<'a, T> DoubleEndedIterator for nom::lib::std::vec::Drain<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::Iter<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::Drain<'a, T> where
    T: 'a, 
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::linked_list::Iter<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::btree_set::Iter<'a, T>
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impl<'a, T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::IterMut<'a, T>
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impl<'a, T, P> DoubleEndedIterator for nom::lib::std::slice::RSplit<'a, T, P> where
    P: FnMut(&T) -> bool
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impl<'a, T, P> DoubleEndedIterator for RSplitMut<'a, T, P> where
    P: FnMut(&T) -> bool
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impl<'a, T, P> DoubleEndedIterator for nom::lib::std::slice::Split<'a, T, P> where
    P: FnMut(&T) -> bool
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impl<'a, T, P> DoubleEndedIterator for SplitMut<'a, T, P> where
    P: FnMut(&T) -> bool
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impl<A> DoubleEndedIterator for RangeInclusive<A> where
    A: Step
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impl<A> DoubleEndedIterator for nom::lib::std::option::IntoIter<A>
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impl<A> DoubleEndedIterator for nom::lib::std::ops::Range<A> where
    A: Step
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impl<A> DoubleEndedIterator for Repeat<A> where
    A: Clone
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impl<A, B> DoubleEndedIterator for Chain<A, B> where
    A: DoubleEndedIterator,
    B: DoubleEndedIterator<Item = <A as Iterator>::Item>, 
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impl<A, B> DoubleEndedIterator for Zip<A, B> where
    A: DoubleEndedIterator + ExactSizeIterator,
    B: DoubleEndedIterator + ExactSizeIterator
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impl<B, I, F> DoubleEndedIterator for FilterMap<I, F> where
    F: FnMut(<I as Iterator>::Item) -> Option<B>,
    I: DoubleEndedIterator
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impl<B, I, F> DoubleEndedIterator for Map<I, F> where
    F: FnMut(<I as Iterator>::Item) -> B,
    I: DoubleEndedIterator
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impl<I> DoubleEndedIterator for Enumerate<I> where
    I: ExactSizeIterator + DoubleEndedIterator
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impl<I> DoubleEndedIterator for Fuse<I> where
    I: DoubleEndedIterator + FusedIterator
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impl<I> DoubleEndedIterator for Fuse<I> where
    I: DoubleEndedIterator
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impl<I> DoubleEndedIterator for Rev<I> where
    I: DoubleEndedIterator
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impl<I> DoubleEndedIterator for Skip<I> where
    I: DoubleEndedIterator + ExactSizeIterator
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impl<I> DoubleEndedIterator for Box<I> where
    I: DoubleEndedIterator + ?Sized
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impl<I, F> DoubleEndedIterator for Inspect<I, F> where
    F: FnMut(&<I as Iterator>::Item),
    I: DoubleEndedIterator
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impl<I, P> DoubleEndedIterator for Filter<I, P> where
    I: DoubleEndedIterator,
    P: FnMut(&<I as Iterator>::Item) -> bool
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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
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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
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impl<K, V> DoubleEndedIterator for nom::lib::std::collections::btree_map::IntoIter<K, V>
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impl<T> DoubleEndedIterator for nom::lib::std::result::IntoIter<T>
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impl<T> DoubleEndedIterator for Once<T>
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impl<T> DoubleEndedIterator for Empty<T>
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impl<T> DoubleEndedIterator for nom::lib::std::collections::vec_deque::IntoIter<T>
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impl<T> DoubleEndedIterator for nom::lib::std::vec::IntoIter<T>
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impl<T> DoubleEndedIterator for nom::lib::std::collections::binary_heap::IntoIter<T>
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impl<T> DoubleEndedIterator for nom::lib::std::collections::btree_set::IntoIter<T>
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impl<T> DoubleEndedIterator for nom::lib::std::collections::linked_list::IntoIter<T>
[src]