Make a class template std::is_swappable

Question

I'm trying to make a class template swappable. I don't understand why the static assertion fails:

#include 

template 
struct A {};

template 
constexpr void
swap (A &, A &) {}

static_assert (std::is_swappable_v >);

int main (){}

It passes with

template 
constexpr void
swap (A&, A&) {}

but shouldn't the first one also be OK?

user_3309790 · Answer

std::is_swappable (and std::is_swappable_with) considers std::swap too.

... are both well-formed in unevaluated context after using std::swap;