DEFINE_HAS_MEMBER_TYPE (macro, +tests)

#include <type_traits>

#define DEFINE_HAS_MEMBER_TYPE(member_type) \
template<typename T, typename = std::void_t<>> \
struct has_##member_type##_member_type : std::false_type { }; \
template<typename T> \
struct has_##member_type##_member_type<T, std::void_t<typename T::member_type>> : std::true_type { }; \
template<typename T> \
constexpr bool has_##member_type##_member_type_v = has_##member_type##_member_type<T>::value;

DEFINE_HAS_MEMBER_TYPE(self)

struct Bad {};
struct Good {
    using self = Good;
};

static_assert(!has_self_member_type<Bad>::value);
static_assert(has_self_member_type_v<Good>);