LWG-3627 Inconsistent specifications for `std::make_optional` overloads

[StephanTLavavej]

LWG-3627 Inconsistent specifications for std::make_optional overloads

[frederick-vs-ja]

I believe the resolution was speculatively implemented in #2607.

STL/stl/inc/optional

Line 983 in ab6dec6

_EXPORT_STD template <class _Ty, enable_if_t<is_constructible_v<decay_t<_Ty>, _Ty>, int> = 0> // LWG-3627

However, in C++26 this overload is additionally constrained ([optional.specalg]/3), and thus it's unclear to me whether such wording change still introduces implicit SFINAE constraints.

[StephanTLavavej]

Thanks, then we just need to remove the comments.

I don't understand "Constraints: The call to make_optional does not use an explicit template-argument-list that begins with a type template-argument." at all. How is that even implementable? That sounds like a user restriction.

[timsong-cpp]

Thanks, then we just need to remove the comments.

I don't understand "Constraints: The call to make_optional does not use an explicit template-argument-list that begins with a type template-argument." at all. How is that even implementable? That sounds like a user restriction.

With something like template<int = 0, class T>. The point is to make make_optional<T>(x) always go to one of the other two overloads.