error[E0631]: type mismatch in closure arguments
  --> $DIR/closure-ref-114180.rs:6:15
   |
LL |     let compare = |(a,), (e,)| todo!();
   |                   ------------ found signature defined here
LL |     v.sort_by(compare);
   |       ------- ^^^^^^^ expected due to this
   |       |
   |       required by a bound introduced by this call
   |
   = note: expected closure signature `for<'a, 'b> fn(&'a ({integer},), &'b ({integer},)) -> _`
              found closure signature `fn((_,), (_,)) -> _`
note: required by a bound in `slice::<impl [T]>::sort_by`
  --> $SRC_DIR/alloc/src/slice.rs:LL:COL
help: consider adjusting the signature so it borrows its arguments
   |
LL |     let compare = |&(a,), &(e,)| todo!();
   |                    +      +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0631`.