error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
  --> $DIR/borrowck-loan-vec-content.rs:18:9
   |
LL |     takes_imm_elt(
   |     ------------- immutable borrow later used by call
LL |         &v[0],
   |          - immutable borrow occurs here
LL |         || {
   |         ^^ mutable borrow occurs here
LL |             v[1] = 4;
   |             - second borrow occurs due to use of `v` in closure

error: aborting due to 1 previous error

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