2. mysterious @

Use @ to bind a pattern to a name.

let foo = 4;

match foo {
    x @ 0..=5 => assert_eq!(x,4),
    y @ _ => panic!("{}-too many!", y)
}

let point: (u32,u32) = (1, 2);

match point {
    (1, y @ _) => assert_eq!(y,2),
    _ => {}
}

let point: (u32,u32) = (1, 2);
let mypoint @ (x, _) = point;

assert_eq!(x,1);
assert_eq(mypoint,point);