# Trait std::str::pattern::DoubleEndedSearcher

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    pub trait DoubleEndedSearcher<'a>: ReverseSearcher<'a> { }

🔬This is a nightly-only experimental API. (`pattern` #27721)
Expand description

A marker trait to express that a `ReverseSearcher` can be used for a `DoubleEndedIterator` implementation.

For this, the impl of `Searcher` and `ReverseSearcher` need to follow these conditions:

- All results of `next()` need to be identical to the results of `next_back()` in reverse order.
- `next()` and `next_back()` need to behave as the two ends of a range of values, that is they can not “walk past each other”.

## Examples

`char::Searcher` is a `DoubleEndedSearcher` because searching for a `char` only requires looking at one at a time, which behaves the same from both ends.

`(&str)::Searcher` is not a `DoubleEndedSearcher` because the pattern `"aa"` in the haystack `"aaa"` matches as either `"[aa]a"` or `"a[aa]"`, depending from which side it is searched.

## Implementors§

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### impl<'a> DoubleEndedSearcher<'a> for CharSearcher<'a>

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### impl<'a, 'b> DoubleEndedSearcher<'a> for CharSliceSearcher<'a, 'b>

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### impl<'a, F> DoubleEndedSearcher<'a> for CharPredicateSearcher<'a, F>where F: FnMut(char) -> bool,