The only "unusual" rule here is that Rust offers the zero type addition, but does not provide the (much more complicated) other type additions So Rust does hav

The only "unusual" rule here is that Rust offers the zero type addition, but does not provide the (much more complicated) other type additions So Rust does have: String + ! = String But Rust doesn't have: String + i32 = Either<String,i32> Note that the never type ! isn't special here, Rust will also cheerfully: String + Infallible = String or if you were to define your own empty type like so: enum MyEmptyType {} // MyEmptyType has no possible values Now under type arithmetic String + MyEmptyType = String and indeed that works in Rust. Edited: Syntax fix