1 error[E0369]: cannot add `&str` to `&String`
2 --> $DIR/str-concat-on-double-ref.rs:4:15
7 | | `+` cannot be used to concatenate two `&str` strings
10 = note: string concatenation requires an owned `String` on the left
11 help: create an owned `String` from a string reference
13 LL | let c = a.to_owned() + b;
16 error: aborting due to previous error
18 For more information about this error, try `rustc --explain E0369`.