# Trait std::str::pattern::Pattern

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    pub trait Pattern<'a>: Sized {
        type Searcher: Searcher<'a>;

        // Required method
        fn into_searcher(self, haystack: &'a str) -> Self::Searcher;

        // Provided methods
        fn is_contained_in(self, haystack: &'a str) -> bool { ... }
        fn is_prefix_of(self, haystack: &'a str) -> bool { ... }
        fn is_suffix_of(self, haystack: &'a str) -> bool
           where Self::Searcher: ReverseSearcher<'a> { ... }
        fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> { ... }
        fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>
           where Self::Searcher: ReverseSearcher<'a> { ... }
    }

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

A string pattern.

A `Pattern<'a>` expresses that the implementing type can be used as a string pattern for searching in a `&'a str`.

For example, both `'a'` and `"aa"` are patterns that would match at index `1` in the string `"baaaab"`.

The trait itself acts as a builder for an associated `Searcher` type, which does the actual work of finding occurrences of the pattern in a string.

Depending on the type of the pattern, the behaviour of methods like `str::find` and `str::contains` can change. The table below describes some of those behaviours.

Pattern type | Match condition
--- | ---
`&str` | is substring
`char` | is contained in string
`&[char]` | any char in slice is contained in string
`F: FnMut(char) -> bool` | `F` returns `true` for a char in string
`&&str` | is substring
`&String` | is substring

## Examples

    // &str
    assert_eq!("abaaa".find("ba"), Some(1));
    assert_eq!("abaaa".find("bac"), None);

    // char
    assert_eq!("abaaa".find('a'), Some(0));
    assert_eq!("abaaa".find('b'), Some(1));
    assert_eq!("abaaa".find('c'), None);

    // &[char; N]
    assert_eq!("ab".find(&['b', 'a']), Some(0));
    assert_eq!("abaaa".find(&['a', 'z']), Some(0));
    assert_eq!("abaaa".find(&['c', 'd']), None);

    // &[char]
    assert_eq!("ab".find(&['b', 'a'][..]), Some(0));
    assert_eq!("abaaa".find(&['a', 'z'][..]), Some(0));
    assert_eq!("abaaa".find(&['c', 'd'][..]), None);

    // FnMut(char) -> bool
    assert_eq!("abcdef_z".find(|ch| ch > 'd' && ch < 'y'), Some(4));
    assert_eq!("abcddd_z".find(|ch| ch > 'd' && ch < 'y'), None);

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## Required Associated Types§

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#### type Searcher: Searcher<'a>

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

Associated searcher for this pattern

## Required Methods§

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#### fn into_searcher(self, haystack: &'a str) -> Self::Searcher

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

Constructs the associated searcher from `self` and the `haystack` to search in.

## Provided Methods§

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#### fn is_contained_in(self, haystack: &'a str) -> bool

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

Checks whether the pattern matches anywhere in the haystack

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#### fn is_prefix_of(self, haystack: &'a str) -> bool

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

Checks whether the pattern matches at the front of the haystack

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#### fn is_suffix_of(self, haystack: &'a str) -> bool where Self::Searcher: ReverseSearcher<'a>,

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

Checks whether the pattern matches at the back of the haystack

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#### fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str>

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

Removes the pattern from the front of haystack, if it matches.

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#### fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>where Self::Searcher: ReverseSearcher<'a>,

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

Removes the pattern from the back of haystack, if it matches.

## Object Safety§

This trait is not object safe.

## Implementors§

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### impl<'a> Pattern<'a> for char

Searches for chars that are equal to a given `char`.

#### Examples

    assert_eq!("Hello world".find('o'), Some(4));

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#### type Searcher = CharSearcher<'a>

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### impl<'a, 'b> Pattern<'a> for &'b str

Non-allocating substring search.

Will handle the pattern `""` as returning empty matches at each character boundary.

#### Examples

    assert_eq!("Hello world".find("world"), Some(6));

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#### type Searcher = StrSearcher<'a, 'b>

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### impl<'a, 'b> Pattern<'a> for &'b String

A convenience impl that delegates to the impl for `&str`.

#### Examples

    assert_eq!(String::from("Hello world").find("world"), Some(6));

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#### type Searcher = <&'b str as Pattern<'a>>::Searcher

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### impl<'a, 'b> Pattern<'a> for &'b [char]

Searches for chars that are equal to any of the `char`s in the slice.

#### Examples

    assert_eq!("Hello world".find(&['l', 'l'] as &[_]), Some(2));
    assert_eq!("Hello world".find(&['l', 'l'][..]), Some(2));

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#### type Searcher = CharSliceSearcher<'a, 'b>

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### impl<'a, 'b, 'c> Pattern<'a> for &'c &'b str

Delegates to the `&str` impl.

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#### type Searcher = StrSearcher<'a, 'b>

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### impl<'a, 'b, const N: usize> Pattern<'a> for &'b [char; N]

Searches for chars that are equal to any of the `char`s in the array.

#### Examples

    assert_eq!("Hello world".find(&['o', 'l']), Some(2));
    assert_eq!("Hello world".find(&['h', 'w']), Some(6));

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#### type Searcher = CharArrayRefSearcher<'a, 'b, N>

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### impl<'a, F> Pattern<'a> for Fwhere F: FnMut(char) -> bool,

Searches for `char`s that match the given predicate.

#### Examples

    assert_eq!("Hello world".find(char::is_uppercase), Some(0));
    assert_eq!("Hello world".find(|c| "aeiou".contains(c)), Some(1));

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#### type Searcher = CharPredicateSearcher<'a, F>

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### impl<'a, const N: usize> Pattern<'a> for [char; N]

Searches for chars that are equal to any of the `char`s in the array.

#### Examples

    assert_eq!("Hello world".find(['o', 'l']), Some(2));
    assert_eq!("Hello world".find(['h', 'w']), Some(6));

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#### type Searcher = CharArraySearcher<'a, N>