_ 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.

An example of an _ expression:

#![allow(unused)] fn main() { let p = (1, 2); let mut a = 0; (_, a) = p; }