# Trait std::str::pattern::Searcher [−] [src]

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

        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)

API not fully fleshed out and ready to be stabilized

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

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

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

API not fully fleshed out and ready to be stabilized

Getter for the underlaying string to be searched in

Will always return the same `&str`

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

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

API not fully fleshed out and ready to be stabilized

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

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

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

API not fully fleshed out and ready to be stabilized

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

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

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

API not fully fleshed out and ready to be stabilized

Find the next `Reject` result. See `next()`

## Implementors

- `impl<'a> Searcher<'a> for CharSearcher<'a>`
- `impl<'a, 'b> Searcher<'a> for CharSliceSearcher<'a, 'b>`
- `impl<'a, F> Searcher<'a> for CharPredicateSearcher<'a, F> where
  F: FnMut(char) -> bool,`
- `impl<'a, 'b> Searcher<'a> for StrSearcher<'a, 'b>`

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