warning: value assigned to `b` is never read
  --> $DIR/general.rs:60:25
   |
LL |         (Some(a), &Some(mut b)) => {
   |                         ^^^^^
   |
   = help: maybe it is overwritten before being read?
   = note: `#[warn(unused_assignments)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted