# Trait alloc::str::pattern::Searcher

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    pub unsafe trait Searcher<'a> {
        // Required methods
        fn haystack(&self) -> &'a str;
        fn next(&mut self) -> SearchStep;

        // Provided methods
        fn next_match(&mut self) -> Option<(usize, usize)> { ... }
        fn next_reject(&mut self) -> Option<(usize, usize)> { ... }
    }

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

A searcher for a string pattern.

This trait provides methods for searching for non-overlapping matches of a pattern starting from the front (left) of a string.

It will be implemented by associated `Searcher` types of the `Pattern` trait.

The trait is marked unsafe because the indices returned by the `next()` methods are required to lie on valid utf8 boundaries in the haystack. This enables consumers of this trait to slice the haystack without additional runtime checks.

## Required Methods§

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#### fn haystack(&self) -> &'a str

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

Getter for the underlying string to be searched in

Will always return the same `&str`.

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#### fn next(&mut self) -> SearchStep

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

Performs the next search step starting from the front.

- Returns `Match(a, b)` if `haystack[a..b]` matches the pattern.
- Returns `Reject(a, b)` if `haystack[a..b]` can not match the pattern, even partially.
- Returns `Done` if every byte of the haystack has been visited.

The stream of `Match` and `Reject` values up to a `Done` will contain index ranges that are adjacent, non-overlapping, covering the whole haystack, and laying on utf8 boundaries.

A `Match` result needs to contain the whole matched pattern, however `Reject` results may be split up into arbitrary many adjacent fragments. Both ranges may have zero length.

As an example, the pattern `"aaa"` and the haystack `"cbaaaaab"` might produce the stream `[Reject(0, 1), Reject(1, 2), Match(2, 5), Reject(5, 8)]`

## Provided Methods§

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#### fn next_match(&mut self) -> Option<(usize, usize)>

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

Finds the next `Match` result. See `next()`.

Unlike `next()`, there is no guarantee that the returned ranges of this and `next_reject` will overlap. This will return `(start_match, end_match)`, where start_match is the index of where the match begins, and end_match is the index after the end of the match.

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#### fn next_reject(&mut self) -> Option<(usize, usize)>

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

Finds the next `Reject` result. See `next()` and `next_match()`.

Unlike `next()`, there is no guarantee that the returned ranges of this and `next_match` will overlap.

## Implementors§

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

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

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### impl<'a, 'b> Searcher<'a> for StrSearcher<'a, 'b>

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### impl<'a, 'b, const N: usize> Searcher<'a> for CharArrayRefSearcher<'a, 'b, N>

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

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### impl<'a, const N: usize> Searcher<'a> for CharArraySearcher<'a, N>