I saw this by the way:
Aside: Just before Rust 1.0.0, someone actually implemented Add for String
to mean concatenation. It took yours truly (among others) a heartrending plea
to the Rust gods until they mended this particular error.
+ for String and Vec were implemented some while before Rust 1.0. Add for String still exists and is stable; it was Add for Vec that we removed. (And we said we would revisit the issue of whether to have
+ on Vec or not, after Rust 1.0).