Binding - Rust By Example
Description: A description

# Binding

Indirectly accessing a variable makes it impossible to branch and use that variable without re-binding. `match` provides the `@` sigil for binding values to names:

    // A function `age` which returns a `u32`.
    fn age() -> u32 {
        15
    }

    fn main() {
        println!("Tell me what type of person you are");

        match age() {
            0             => println!("I haven't celebrated my first birthday yet"),
            // Could `match` 1 ..= 12 directly but then what age
            // would the child be? Instead, bind to `n` for the
            // sequence of 1 ..= 12. Now the age can be reported.
            n @ 1  ..= 12 => println!("I'm a child of age {:?}", n),
            n @ 13 ..= 19 => println!("I'm a teen of age {:?}", n),
            // Nothing bound. Return the result.
            n             => println!("I'm an old person of age {:?}", n),
        }
    }

You can also use binding to "destructure" `enum` variants, such as `Option`:

    fn some_number() -> Option<u32> {
        Some(42)
    }

    fn main() {
        match some_number() {
            // Got `Some` variant, match if its value, bound to `n`,
            // is equal to 42.
            Some(n @ 42) => println!("The Answer: {}!", n),
            // Match any other number.
            Some(n)      => println!("Not interesting... {}", n),
            // Match anything else (`None` variant).
            _            => (),
        }
    }

### See also:

`functions`, `enums` and `Option`