cpp-opaque-typedef/include/opaque_typedef/traits.hpp

//
//  traits.hpp
//  opaque_typedef
//
//  Created by Sam Jaffe on 12/1/23.
//  Copyright © 2023 Sam Jaffe. All rights reserved.
//

#pragma once

#include <type_traits>

#define REQUIRES(...) typename = std::enable_if_t<__VA_ARGS__>

namespace types {
  template <typename Base, typename = void> struct underlying_type {
    using type = Base const &;
  };

  template <typename Base>
  struct underlying_type<Base, std::void_t<typename Base::underlying_type>> {
    using type = typename Base::underlying_type;
  };

  template <typename Base>
  using underlying_type_t = typename underlying_type<Base>::type;
}