#pragma once #include <type_traits> #include <nlohmann/detail/meta/void_t.hpp> // http://en.cppreference.com/w/cpp/experimental/is_detected namespace nlohmann { namespace detail { struct nonesuch { nonesuch() = delete; ~nonesuch() = delete; nonesuch(nonesuch const&) = delete; void operator=(nonesuch const&) = delete; }; template <class Default, class AlwaysVoid, template <class...> class Op, class... Args> struct detector { using value_t = std::false_type; using type = Default; }; 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 detector<nonesuch, void, Op, Args...>::value_t; template <template <class...> class Op, class... Args> using detected_t = typename detector<nonesuch, void, Op, Args...>::type; template <class Default, template <class...> class Op, class... Args> using detected_or = detector<Default, void, Op, Args...>; template <class Default, template <class...> class Op, class... Args> using detected_or_t = typename detected_or<Default, Op, Args...>::type; template <class Expected, template <class...> class Op, class... Args> using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>; template <class To, template <class...> class Op, class... Args> using is_detected_convertible = std::is_convertible<detected_t<Op, Args...>, To>; } }