https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120917
--- Comment #17 from Frank Heckenbach <f.heckenb...@fh-soft.de> --- Maybe I've found a work-around. I took the is_instance_of_v template from https://indii.org/blog/is-type-instantiation-of-template/ and turned it into a concept, so I can replace: void f (S <auto>); void g (T <auto, auto>); with: void f (instance_of <S> auto); void g (instance_of <T> auto); which at least keeps the required changes localized. I think it won't work with "partially auto instantiations" such as: void g (T <auto, int>); But fortunately I don't have many of them. Since I'm not so well versed with concepts yet, can you please confirm whether this is effectively equivalent? % cat test.cpp #include <type_traits> template<typename T, template<typename...> typename U> inline constexpr bool is_instance_of_v = std::false_type{}; template<template<typename...> typename U, typename... Vs> inline constexpr bool is_instance_of_v<U<Vs...>,U> = std::true_type{}; template <typename T, template<typename...> typename U> concept instance_of = is_instance_of_v<T, U>; template <typename T> struct S { }; void f (S <auto>) { } void f_ (instance_of <S> auto) { } int main () { S <double> a; // OK f (a); f_ (a); f (S <int> ()); f_ (S <int> ()); // error // f (1); // f_ (1); // f (nullptr); // f_ (nullptr); } % g++-14 --std=c++23 -c -Wall -Wextra -pedantic -Wpedantic -pedantic-errors -fconcepts-ts test.cpp cc1plus: note: '-fconcepts-ts' is deprecated and will be removed in GCC 15; please convert your code to C++20 concepts %
