mlTemplateHelpers.h

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**
** Copyright 2021, MeVis Medical Solutions AG
**
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#pragma once
 
#include "mlTypeDefs.h"
 
ML_START_NAMESPACE
 
/*
 * Utility template for easier use within std::visit.
 * See https://en.cppreference.com/w/cpp/utility/variant/visit
 */
template <class... Ts> struct Overload : Ts...
{
  using Ts::operator()...;
};
template <class... Ts> Overload(Ts...)->Overload<Ts...>;
 
//
// the following implements the C++ standard 17 proposal N4502
// For further information see https://en.cppreference.com/w/cpp/experimental/is_detected
 
namespace internal
{
 
#if __GNUC__ < 5 && !defined __clang__
  // http://stackoverflow.com/a/28967049/1353549
  template <typename...>
  struct voider {
    using type = void;
  };
  template <typename... Ts>
  using void_t = typename voider<Ts...>::type;
#else
  template <typename...>
  using void_t = void;
#endif
 
  struct nonesuch {
    nonesuch() = delete;
    ~nonesuch() = delete;
    nonesuch(nonesuch const&) = delete;
    void operator=(nonesuch const&) = delete;
  };
 
  // primary template handles all types not supporting the archetypal Op:
  template <class Default, class, template <class...> class Op, class... Args>
  struct detector {
    using value_t = std::false_type;
    using type = Default;
  };
 
  // the specialization recognizes and handles only types supporting Op:
  template <class Default, template <class...> class Op, class... Args>
  struct detector<Default, void_t<Op<Args...>>, Op, Args...> {
    using value_t = std::true_type;
    using type = Op<Args...>;
  };
}
 
template <template <class...> class Op, class... Args>
using is_detected = typename internal::detector<internal::nonesuch, void, Op, Args...>::value_t;
 
template <template <class...> class Op, class... Args>
constexpr bool is_detected_v = is_detected<Op, Args...>::value;
 
template <template <class...> class Op, class... Args>
using detected_t = typename internal::detector<internal::nonesuch, void, Op, Args...>::type;
 
 
 
ML_END_NAMESPACE