I'm not really convinced. In C++, you could start your hypothetical format function with static_assert(formatter<T>:: exists) or similar and get a very similar error message. (In C++ template terminology, a class like that is also called a trait, funnily enough, but that's just a convention rather than a language feature.) I think you could use C++ concepts to check add part of the function signature, but the functional difference would be very small. And none of these – including Rust traits – help you with compile time checking of format specifiers.
