Strange MSVC behaviour with std::experimental::is_detected

Question

I implemented std::experimental::is_detected based on this article on cppreference.com (Part of the code is below + working repro).

It works well on G++

Answer 1

Here's a workaround that appears to work with recent MSVC (tested with Visual C++ 19.00.23720.0):

#include 

template 
using void_t = void;

namespace internal
{
    template 
    struct detect_impl
    {
        using value_t = V;
        using type = D;
    };

    template  class Check, typename... Args>
    auto detect_check(char)
        -> detect_impl;

    template  class Check, typename... Args>
    auto detect_check(int)
        -> decltype(void_t>(),
                    detect_impl>{});

    template  class Check, typename... Args>
    struct detect : decltype(detect_check(0)) {};
}

struct nonesuch
{
    nonesuch() = delete;
    ~nonesuch() = delete;
    nonesuch(nonesuch const&) = delete;
    void operator=(nonesuch const&) = delete;
};

template  class Check, typename... Args>
using is_detected = typename internal::detect::value_t;

(The dummy void parameter is unused now, it's there just to keep the rest of the implementation intact.)