绑定

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)      => println!("Not interesting... {}", n),
        // Match anything else (`None` variant).
        _            => (),
}