https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101539
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I've tried my testcases with MSVC on godbolt that claims to implement it, and https://godbolt.org/z/3PnjM33vM for the first testcase shows it disagrees with my expectations on static_assert (std::is_pointer_interconvertible_base_of_v<D, F>); static_assert (std::is_pointer_interconvertible_base_of_v<E, F>); static_assert (!std::is_pointer_interconvertible_base_of_v<D, G>); static_assert (!std::is_pointer_interconvertible_base_of_v<D, I>); static_assert (std::is_pointer_interconvertible_base_of_v<H, volatile I>); Is that a bug in my patch or is MSVC buggy on these (or mix thereof)? https://godbolt.org/z/aYeYnne9d shows the second testcase, here it differs on: static_assert (std::is_pointer_interconvertible_with_class<F, int> (&F::b)); static_assert (std::is_pointer_interconvertible_with_class<I, int> (&I::g)); static_assert (std::is_pointer_interconvertible_with_class<L, int> (&L::b)); static_assert (std::is_pointer_interconvertible_with_class (&V::a)); static_assert (std::is_pointer_interconvertible_with_class (&V::b)); Again, my bug, MSVC bug, mix thereof? Oh, and there is another thing, the standard has an example: struct A { int a; }; // a standard-layout class struct B { int b; }; // a standard-layout class struct C: public A, public B { }; // not a standard-layout class static_assert( is_pointer_interconvertible_with_class( &C::b ) ); // Succeeds because, despite its appearance, &C::b has type // “pointer to member of B of type int”. static_assert( is_pointer_interconvertible_with_class<C>( &C::b ) ); // Forces the use of class C, and fails. It seems to work as written with MSVC (second assertion fails), but fails with GCC with the patch: /tmp/1.C:22:57: error: no matching function for call to ‘is_pointer_interconvertible_with_class<C>(int B::*)’ 22 | static_assert( is_pointer_interconvertible_with_class<C>( &C::b ) ); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~ /tmp/1.C:8:1: note: candidate: ‘template<class S, class M> constexpr bool std::is_pointer_interconvertible_with_class(M S::*)’ 8 | is_pointer_interconvertible_with_class (M S::*m) noexcept | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /tmp/1.C:8:1: note: template argument deduction/substitution failed: /tmp/1.C:22:57: note: mismatched types ‘C’ and ‘B’ 22 | static_assert( is_pointer_interconvertible_with_class<C>( &C::b ) ); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~ the second int argument isn't deduced. This boils down to: template <class S, class M> bool foo (M S::*m) noexcept; struct A { int a; }; struct B { int b; }; struct C : public A, public B {}; bool a = foo (&C::b); bool b = foo<C, int> (&C::b); bool c = foo<C> (&C::b); which with /std:c++20 or -std=c++20 is accepted by latest MSVC and ICC but rejected by GCC and clang (in both cases on the last line).
