1 error[E0369]: binary operation `+` cannot be applied to type `&std::string::String`
2 --> $DIR/str-concat-on-double-ref.rs:14:13
7 = note: an implementation of `std::ops::Add` might be missing for `&std::string::String`
9 error: aborting due to previous error
11 For more information about this error, try `rustc --explain E0369`.