> I don't know if such shape-shifting is allowed in Rust I think so! You mean this? let mut x: Result <bool, String> = Ok (false); dbg! (&x); //

> I don't know if such shape-shifting is allowed in Rust I think so! You mean this? let mut x: Result <bool, String> = Ok (false); dbg! (&x); // Get a reference to the bool and mutate it if let Ok (b) = &mut x { *b = true; } dbg! (&x); // "shape-shift" to the other enum variant x = Err ("No boolean :(".to_string ()); dbg! (&x); It runs in Godbolt https://godbolt.org/z/q6jqYdYh1 https://godbolt.org/z/q6jqYdYh1