_
expressions
Syntax
UnderscoreExpression :
_
Underscore expressions, denoted with the symbol _
, are used to signify a
placeholder in a destructuring assignment. They may only appear in the left-hand
side of an assignment.
Note that this is distinct from the wildcard pattern.
Examples of _
expressions:
#![allow(unused)] fn main() { let p = (1, 2); let mut a = 0; (_, a) = p; struct Position { x: u32, y: u32, } Position { x: a, y: _ } = Position{ x: 2, y: 3 }; // unused result, assignment to `_` used to declare intent and remove a warning _ = 2 + 2; // triggers unused_must_use warning // 2 + 2; // equivalent technique using a wildcard pattern in a let-binding let _ = 2 + 2; }