gcc/clang都输出0/1，我迷茫了。

#include <variant>
#include <iostream>
#include <type_traits>
 
struct C1
{
    struct A
    {
        int a = 0;
    };
 
    std::variant<A> var;
};
 
struct C2
{
    struct A
    {
        int a = 0;
    };
 
    std::variant<std::monostate, A> var;
};
 
int main()
{
    std::cout << std::is_default_constructible_v<C1::A> << std::endl; // prints 0
    std::cout << std::is_default_constructible_v<C2::A> << std::endl; // prints 1
    return 0;
}

--
FROM 158.140.1.*