error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
  --> $DIR/borrowck-loan-vec-content.rs:28:9
   |
LL |         &v[0],
   |          - immutable borrow occurs here
LL |         || { //~ ERROR cannot borrow `v` as mutable
   |         ^^ mutable borrow occurs here
LL |             v[1] = 4;
   |             - borrow occurs due to use of `v` in closure
LL |         })
   |          - immutable borrow ends here

error: aborting due to previous error

For more information about this error, try `rustc --explain E0502`.