one thing you can reason about a function is: does it exist at all? if you don't have parametricity, you can't even be sure about that. in Rust, as long as your

one thing you can reason about a function is: does it exist at all? if you don't have parametricity, you can't even be sure about that. in Rust, as long as your type satisfies a generic function's bounds, you can be sure instantiating that function with this type will compile; in C++ you don't have that luxury.