https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104255
--- Comment #4 from qingzhe huang <nickhuang99 at hotmail dot com> --- (In reply to Patrick Palka from comment #2) > > error: use of parameter outside function body before ‘)’ token > > due to 'e' being used outside of an unevaluated context within the signature > of the function. Sorry for my being unable to grasp your meaning before. Now I can see your point that the "e" of A<f(e)> is from declaration of parameter of function "g". Now that we agree the value from parameter clause should not be used in trailing return type, then it should also not be used in requires clause etc. (https://eel.is/c++draft/basic.scope.param#1.3) But this works: template<typename T> auto f(int n) requires (n>0); This is violating our assumption. So, I am not convinced that (https://eel.is/c++draft/basic.scope.param#note-1) "A function parameter cannot be used for its value within the parameter-declaration-clause" is really meaningful. Or I misunderstand it??? https://www.godbolt.org/z/759oGdr94
