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1 | // Copyright Matt Borland 2021. |
2 | // Use, modification and distribution are subject to the | |
3 | // Boost Software License, Version 1.0. (See accompanying file | |
4 | // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
5 | // | |
6 | // https://en.cppreference.com/w/cpp/experimental/is_detected | |
7 | ||
8 | #ifndef BOOST_MATH_TOOLS_IS_DETECTED_HPP | |
9 | #define BOOST_MATH_TOOLS_IS_DETECTED_HPP | |
10 | ||
11 | #include <type_traits> | |
12 | ||
13 | namespace boost { namespace math { namespace tools { | |
14 | ||
15 | template <typename...> | |
16 | using void_t = void; | |
17 | ||
18 | namespace detail { | |
19 | ||
20 | template <typename Default, typename AlwaysVoid, template<typename...> class Op, typename... Args> | |
21 | struct detector | |
22 | { | |
23 | using value_t = std::false_type; | |
24 | using type = Default; | |
25 | }; | |
26 | ||
27 | template <typename Default, template<typename...> class Op, typename... Args> | |
28 | struct detector<Default, void_t<Op<Args...>>, Op, Args...> | |
29 | { | |
30 | using value_t = std::true_type; | |
31 | using type = Op<Args...>; | |
32 | }; | |
33 | ||
34 | } // Namespace detail | |
35 | ||
36 | // Special type to indicate detection failure | |
37 | struct nonesuch | |
38 | { | |
39 | nonesuch() = delete; | |
40 | ~nonesuch() = delete; | |
41 | nonesuch(const nonesuch&) = delete; | |
42 | void operator=(const nonesuch&) = delete; | |
43 | }; | |
44 | ||
45 | template <template<typename...> class Op, typename... Args> | |
46 | using is_detected = typename detail::detector<nonesuch, void, Op, Args...>::value_t; | |
47 | ||
48 | template <template<typename...> class Op, typename... Args> | |
49 | using detected_t = typename detail::detector<nonesuch, void, Op, Args...>::type; | |
50 | ||
51 | template <typename Default, template<typename...> class Op, typename... Args> | |
52 | using detected_or = detail::detector<Default, void, Op, Args...>; | |
53 | ||
54 | }}} // Namespaces boost math tools | |
55 | ||
56 | #endif // BOOST_MATH_TOOLS_IS_DETECTED_HPP |