Imported Upstream version 1.5.0+dfsg1

[rustc.git] / src / doc / trpl / slice-patterns.md

% Slice patterns

If you want to match against a slice or array, you can use `&` with the
`slice_patterns` feature:

```rust
#![feature(slice_patterns)]

fn main() {
    let v = vec!["match_this", "1"];

    match &v[..] {
        ["match_this", second] => println!("The second element is {}", second),
        _ => {},
    }
}
```

The `advanced_slice_patterns` gate lets you use `..` to indicate any number of
elements inside a pattern matching a slice. This wildcard can only be used once
for a given array. If there's an identifier before the `..`, the result of the
slice will be bound to that name. For example:

```rust
#![feature(advanced_slice_patterns, slice_patterns)]

fn is_symmetric(list: &[u32]) -> bool {
    match list {
        [] | [_] => true,
        [x, inside.., y] if x == y => is_symmetric(inside),
        _ => false
    }
}

fn main() {
    let sym = &[0, 1, 4, 2, 4, 1, 0];
    assert!(is_symmetric(sym));

    let not_sym = &[0, 1, 7, 2, 4, 1, 0];
    assert!(!is_symmetric(not_sym));
}
```