The other alternative here which is why I think this is kind of ridiculous is 9/10 you can just change the function you’re calling to pass a copy rather than passing a reference if that’s what you really want.

...That's a pretty good point. Use the type system to work for you. If you want a value thing, just get it by-value. No need for macros, no need for wildcard ampersands, no need for constexpr constinit consteval static inline noexcept(noexcept(...)) requires(requires(...)) explicit(explicit(...)) { body } -> decltype(body).