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#include <cstddef>
 
#define alignas(...) __attribute__((__aligned__(alignof(decltype(::wheels::detail::get_type_with_alignment<__VA_ARGS__>())))))
 
namespace wheels {
    namespace detail {
        template <std::size_t N> struct __attribute__((__aligned__(N))) alignment_type {};
        template <typename T> T get_type_with_alignment();
        template <std::size_t N> alignment_type<N> get_type_with_alignment();
    }
}
 
struct alignas(8) foo {};
struct alignas(int) bar {};
 
struct qux {
    alignas(2) char frob;
};
 
static_assert(alignof(foo) == 8, "");
static_assert(alignof(bar) == alignof(int), "");
static_assert(alignof(qux) == 2, "");
 
int main() {}
 

prog.cpp: In instantiation of 'wheels::detail::alignment_type<8u>':
prog.cpp:13:8:   instantiated from here
prog.cpp:7:88: error: requested alignment is not a constant
prog.cpp: In instantiation of 'wheels::detail::alignment_type<2u>':
prog.cpp:17:5:   instantiated from here
prog.cpp:7:88: error: requested alignment is not a constant
prog.cpp:20:1: error: static assertion failed: ""
prog.cpp:22:1: error: static assertion failed: ""

Standard output is empty