recursive.hpp

#pragma once
#include <boost/pfr/core.hpp>
#include <boost/pfr/tuple_size.hpp>
 
namespace bugui
{
template <auto C, typename Tp>
concept recursive =
    [] <typename T> (this const auto& self) consteval
{
  using namespace std;
  using namespace boost;
 
  return C.template operator()<T>()
         || [&self] <size_t... I> (index_sequence<I...>) consteval
  { return ((self.template operator()
             <typename pfr::tuple_element_t<I, T>>())
            || ...);
  } (make_index_sequence<pfr::tuple_size_v<T>>{});
}.template operator()<Tp>();
 
#define TO_LAMBDA(ThisConcept)      \
[] <typename Concept> () consteval  \
{ return ThisConcept<Concept>; }
 
#define RECURSIVE_CONCEPT(ThisConcept, Tp) \
recursive<TO_LAMBDA(ThisConcept), Tp>
 
} // namespace bugui