error[E0507]: cannot move out of a shared reference
  --> $DIR/issue-51415.rs:7:42
   |
LL |     let opt = a.iter().enumerate().find(|(_, &s)| {
   |                                          ^^^^^-^
   |                                               |
   |                                               data moved here
   |                                               move occurs because `s` has type `String`, which does not implement the `Copy` trait
   |
help: consider borrowing the pattern binding
   |
LL |     let opt = a.iter().enumerate().find(|(_, &ref s)| {
   |                                               +++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0507`.