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?
        // Could `match` n and use an `if` guard, but would
        // not contribute to exhaustiveness checks.
        // (Although in this case that would not matter since
        // a "catch-all" pattern is present at the bottom)
        // 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.
        // Could also use `Some(42)` and print `"The Awnser: 42!"`
        // but that would require changing `42` in 2 spots should
        // you ever wish to change it.
        // Could also use `Some(n) if n == 42` and print `"The Awnser: {n}!"`
        // but that would not contribute to exhaustiveness checks.
        // (Although in this case that would not matter since
        // the next arm is a "catch-all" pattern)
        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