Oops, SFINAE doesn't work even in `using type =
has_or_has_no_type<T>::type;`.

Let me modify a bit:

template <class T>
struct X {
   static consteval std::meta::info evaluate()
   { if (std::meta::is_same_type(^^T, ^^int)) return { }; else ... }

   static constexpr auto result = evaluate();
};
template <class T> concept C = requires { typename [: X<T>::result :]; };
static_assert(!C<int>); // *error: *cannot splice a null reflection


On 9/17/26 00:20, Bingzhi wrote:
> template <class T>
> struct X {
> static consteval std::meta::info evaluate()
> { if (std::meta::is_same_type(^^T, ^^int)) return { }; else ... }
>
> using type = [: evaluate() :];
> };
> template <class T> concept C = requires { typename X<T>::type; };
> static_assert(!C<int>); // *error: *cannot splice a null reflection
>
>
> I don't know why it is. Can somebody explain?