True, but it's entirely voluntary: - clamp(a, b, c), where a, b, c are all l-values would copy everything. Not destructive by default (but wasteful on "big" ty

True, but it's entirely voluntary: - clamp(a, b, c), where a, b, c are all l-values would copy everything. Not destructive by default (but wasteful on "big" types). - clamp(a, std::move(b), c) would potentially destroy b, but that's something the caller explicitly opted into. - clamp(a, T{ something }, T{ something else }) would be an implicit move, but nobody is going to accidentally use those r-values anywhere else. The non-const ref version returning is not something I quite like either; it would make more sense to me to have `void clamp(T& x, T const& l, T const& h)`, where the semantics would be more like `x.clamp(l, h);`. But to retain the same API I returned the reference.