std::experimental::reflect::Object
From cppreference.com
                    
                                        
                    < cpp | experimental | reflect
                    
                                                            
                    |   Defined in header  <experimental/reflect>
  | 
||
|   template< class T > concept Object = /* see below */;  | 
(reflection TS) | |
The Object concept is satisfied if and only if T is a meta-object type.
Example
Run this code
#include <experimental/reflect> namespace reflect = std::experimental::reflect; template<reflect::Object M> struct meta_t { template<reflect::Object M1> friend constexpr bool operator==(meta_t, meta_t<M1>) noexcept { return reflect::reflects_same_v<M, M1>; } template<reflect::Object M1> friend constexpr bool operator!=(meta_t, meta_t<M1>) noexcept { return !reflect::reflects_same_v<M, M1>; } }; template<reflect::Object M> constexpr meta_t<M> meta{}; int main() { static_assert(meta<reflexpr(int)> == meta<reflexpr(signed int)>, ""); // meta<int>; // error: int is not a meta-object type }