Horizon
detected.hpp
1 #pragma once
2 
3 #include <type_traits>
4 
5 #include <nlohmann/detail/meta/void_t.hpp>
6 
7 // http://en.cppreference.com/w/cpp/experimental/is_detected
8 namespace nlohmann
9 {
10 namespace detail
11 {
12 struct nonesuch
13 {
14  nonesuch() = delete;
15  ~nonesuch() = delete;
16  nonesuch(nonesuch const&) = delete;
17  nonesuch(nonesuch const&&) = delete;
18  void operator=(nonesuch const&) = delete;
19  void operator=(nonesuch&&) = delete;
20 };
21 
22 template <class Default,
23  class AlwaysVoid,
24  template <class...> class Op,
25  class... Args>
26 struct detector
27 {
28  using value_t = std::false_type;
29  using type = Default;
30 };
31 
32 template <class Default, template <class...> class Op, class... Args>
33 struct detector<Default, void_t<Op<Args...>>, Op, Args...>
34 {
35  using value_t = std::true_type;
36  using type = Op<Args...>;
37 };
38 
39 template <template <class...> class Op, class... Args>
40 using is_detected = typename detector<nonesuch, void, Op, Args...>::value_t;
41 
42 template <template <class...> class Op, class... Args>
43 using detected_t = typename detector<nonesuch, void, Op, Args...>::type;
44 
45 template <class Default, template <class...> class Op, class... Args>
46 using detected_or = detector<Default, void, Op, Args...>;
47 
48 template <class Default, template <class...> class Op, class... Args>
49 using detected_or_t = typename detected_or<Default, Op, Args...>::type;
50 
51 template <class Expected, template <class...> class Op, class... Args>
52 using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;
53 
54 template <class To, template <class...> class Op, class... Args>
55 using is_detected_convertible =
56  std::is_convertible<detected_t<Op, Args...>, To>;
57 } // namespace detail
58 } // namespace nlohmann
nlohmann::detail::value_t
value_t
the JSON type enumeration
Definition: value_t.hpp:42
nlohmann
namespace for Niels Lohmann
Definition: adl_serializer.hpp:9
nlohmann::detail::detector
Definition: detected.hpp:27
nlohmann::detail::nonesuch
Definition: detected.hpp:13