Non-type template parameter pack for class data member pointer can't compile with gcc

Question

I try to write a code with c++17 auto non-type template parameter pack for class data member pointer, but the following code clang will compile and gcc will not, you can see godbolt for error message , can somebody tell me which one should I believe since I can't figure out why gcc reject this.

Thanks for you help.

template <
    typename B,
    template <auto B::*...> typename Wrapper, 
    auto B::*... Args
>
void f(Wrapper<Args...>) {}

template <auto... Args> struct Wrapper {};
struct A { int i; float f; };

// gcc error: unable to deduce 'auto B::*' from '&A::i'
f(Wrapper<&A::i, &A::f>{});

I know that if change <auto B::*...> to <auto...> then both can compile, but I want know why gcc couldn't deduce correct type since the following non-auto template parameter get same situation: gcc can't compile and clang can:

template <
    typename B,
    typename... MT,
    template <MT B::*...> class Wrapper, 
    MT B::*... Args
>
void f(Wrapper<Args...>) {}

Answer 1

Try with

template <
    template <auto ...> typename Wrapper, 
    auto ... Args
>
void f(Wrapper<Args...>) {}

auto is an alternative for B::* ; so you should use auto or B::* , not both.