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:
let p = (1, 2);
let mut a = 0;
(_, a) = p;