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7c673cae FG |
1 | /*! |
2 | @file | |
3 | Adapts `std::integral_constant` for use with Hana. | |
4 | ||
b32b8144 | 5 | @copyright Louis Dionne 2013-2017 |
7c673cae FG |
6 | Distributed under the Boost Software License, Version 1.0. |
7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
8 | */ | |
9 | ||
10 | #ifndef BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP | |
11 | #define BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP | |
12 | ||
13 | #include <boost/hana/concept/integral_constant.hpp> | |
14 | #include <boost/hana/config.hpp> | |
15 | #include <boost/hana/core/when.hpp> | |
16 | #include <boost/hana/fwd/core/to.hpp> | |
17 | #include <boost/hana/fwd/core/tag_of.hpp> | |
18 | #include <boost/hana/fwd/integral_constant.hpp> | |
19 | ||
20 | #include <type_traits> | |
21 | ||
22 | ||
23 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
24 | namespace std { | |
25 | //! @ingroup group-ext-std | |
26 | //! Adapter for `std::integral_constant`s. | |
27 | //! | |
28 | //! Provided models | |
29 | //! --------------- | |
30 | //! 1. `Constant` and `IntegralConstant`\n | |
31 | //! A `std::integral_constant` is a model of the `IntegralConstant` and | |
32 | //! `Constant` concepts, just like `hana::integral_constant`s are. As a | |
33 | //! consequence, they are also implicitly a model of the concepts provided | |
34 | //! for all models of `Constant`. | |
35 | //! @include example/ext/std/integral_constant.cpp | |
36 | template <typename T, T v> | |
37 | struct integral_constant { }; | |
38 | } | |
39 | #endif | |
40 | ||
41 | ||
42 | BOOST_HANA_NAMESPACE_BEGIN | |
43 | namespace ext { namespace std { | |
44 | template <typename T> | |
45 | struct integral_constant_tag { using value_type = T; }; | |
46 | }} | |
47 | ||
48 | namespace detail { | |
49 | template <typename T, T v> | |
50 | constexpr bool | |
51 | is_std_integral_constant(std::integral_constant<T, v>*) | |
52 | { return true; } | |
53 | ||
54 | constexpr bool is_std_integral_constant(...) | |
55 | { return false; } | |
56 | ||
57 | ||
58 | template <typename T, T v> | |
59 | constexpr bool | |
60 | is_hana_integral_constant(hana::integral_constant<T, v>*) | |
61 | { return true; } | |
62 | ||
63 | constexpr bool is_hana_integral_constant(...) | |
64 | { return false; } | |
65 | } | |
66 | ||
67 | template <typename T> | |
68 | struct tag_of<T, when< | |
69 | detail::is_std_integral_constant((T*)0) && | |
70 | !detail::is_hana_integral_constant((T*)0) | |
71 | >> { | |
72 | using type = ext::std::integral_constant_tag< | |
73 | typename hana::tag_of<typename T::value_type>::type | |
74 | >; | |
75 | }; | |
76 | ||
77 | ////////////////////////////////////////////////////////////////////////// | |
78 | // Constant/IntegralConstant | |
79 | ////////////////////////////////////////////////////////////////////////// | |
80 | template <typename T> | |
81 | struct IntegralConstant<ext::std::integral_constant_tag<T>> { | |
82 | static constexpr bool value = true; | |
83 | }; | |
84 | ||
85 | template <typename T, typename C> | |
86 | struct to_impl<ext::std::integral_constant_tag<T>, C, when< | |
87 | hana::IntegralConstant<C>::value | |
88 | >> : embedding<is_embedded<typename C::value_type, T>::value> { | |
89 | template <typename N> | |
90 | static constexpr auto apply(N const&) { | |
91 | return std::integral_constant<T, N::value>{}; | |
92 | } | |
93 | }; | |
94 | BOOST_HANA_NAMESPACE_END | |
95 | ||
96 | #endif // !BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP |