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1 | /*! |
2 | @file | |
3 | Adapts `std::integer_sequence` for use with Hana. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
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_INTEGER_SEQUENCE_HPP | |
11 | #define BOOST_HANA_EXT_STD_INTEGER_SEQUENCE_HPP | |
12 | ||
13 | #include <boost/hana/bool.hpp> | |
14 | #include <boost/hana/config.hpp> | |
15 | #include <boost/hana/detail/fast_and.hpp> | |
16 | #include <boost/hana/ext/std/integral_constant.hpp> | |
17 | #include <boost/hana/fwd/at.hpp> | |
18 | #include <boost/hana/fwd/core/tag_of.hpp> | |
19 | #include <boost/hana/fwd/drop_front.hpp> | |
20 | #include <boost/hana/fwd/equal.hpp> | |
21 | #include <boost/hana/fwd/is_empty.hpp> | |
22 | #include <boost/hana/fwd/unpack.hpp> | |
23 | ||
24 | #include <cstddef> | |
25 | #include <type_traits> | |
26 | #include <utility> | |
27 | ||
28 | ||
29 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
30 | namespace std { | |
31 | //! @ingroup group-ext-std | |
32 | //! Adaptation of `std::integer_sequence` for Hana. | |
33 | //! | |
34 | //! | |
35 | //! | |
36 | //! Modeled concepts | |
37 | //! ---------------- | |
38 | //! 1. `Comparable`\n | |
39 | //! Two `std::integer_sequence`s are equal if and only if they have the | |
40 | //! same number of elements, and if corresponding elements compare equal. | |
41 | //! The types of the elements held in both `integer_sequence`s may be | |
42 | //! different, as long as they can be compared. | |
43 | //! @include example/ext/std/integer_sequence/comparable.cpp | |
44 | //! | |
45 | //! 2. `Foldable`\n | |
46 | //! Folding an `integer_sequence` is equivalent to folding a sequence of | |
47 | //! `std::integral_constant`s with the corresponding types. | |
48 | //! @include example/ext/std/integer_sequence/foldable.cpp | |
49 | //! | |
50 | //! 3. `Iterable`\n | |
51 | //! Iterating over an `integer_sequence` is equivalent to iterating over | |
52 | //! a sequence of the corresponding `std::integral_constant`s. | |
53 | //! @include example/ext/std/integer_sequence/iterable.cpp | |
54 | //! | |
55 | //! 4. `Searchable`\n | |
56 | //! Searching through an `integer_sequence` is equivalent to searching | |
57 | //! through the corresponding sequence of `std::integral_constant`s. | |
58 | //! @include example/ext/std/integer_sequence/searchable.cpp | |
59 | template <typename T, T ...v> | |
60 | struct integer_sequence { }; | |
61 | } | |
62 | #endif | |
63 | ||
64 | ||
65 | BOOST_HANA_NAMESPACE_BEGIN | |
66 | namespace ext { namespace std { struct integer_sequence_tag; }} | |
67 | ||
68 | template <typename T, T ...v> | |
69 | struct tag_of<std::integer_sequence<T, v...>> { | |
70 | using type = ext::std::integer_sequence_tag; | |
71 | }; | |
72 | ||
73 | ////////////////////////////////////////////////////////////////////////// | |
74 | // Comparable | |
75 | ////////////////////////////////////////////////////////////////////////// | |
76 | template <> | |
77 | struct equal_impl<ext::std::integer_sequence_tag, ext::std::integer_sequence_tag> { | |
78 | template <typename X, X ...xs, typename Y, Y ...ys> | |
79 | static constexpr hana::bool_<detail::fast_and<(xs == ys)...>::value> | |
80 | apply(std::integer_sequence<X, xs...> const&, std::integer_sequence<Y, ys...> const&) | |
81 | { return {}; } | |
82 | ||
83 | template <typename Xs, typename Ys> | |
84 | static constexpr hana::false_ apply(Xs const&, Ys const&, ...) | |
85 | { return {}; } | |
86 | }; | |
87 | ||
88 | ////////////////////////////////////////////////////////////////////////// | |
89 | // Foldable | |
90 | ////////////////////////////////////////////////////////////////////////// | |
91 | template <> | |
92 | struct unpack_impl<ext::std::integer_sequence_tag> { | |
93 | template <typename T, T ...v, typename F> | |
94 | static constexpr decltype(auto) | |
95 | apply(std::integer_sequence<T, v...> const&, F&& f) { | |
96 | return static_cast<F&&>(f)(std::integral_constant<T, v>{}...); | |
97 | } | |
98 | }; | |
99 | ||
100 | ////////////////////////////////////////////////////////////////////////// | |
101 | // Iterable | |
102 | ////////////////////////////////////////////////////////////////////////// | |
103 | template <> | |
104 | struct at_impl<ext::std::integer_sequence_tag> { | |
105 | template <typename T, T ...v, typename N> | |
106 | static constexpr auto apply(std::integer_sequence<T, v...> const&, N const&) { | |
107 | constexpr std::size_t n = N::value; | |
108 | constexpr T values[] = {v...}; | |
109 | return std::integral_constant<T, values[n]>{}; | |
110 | } | |
111 | }; | |
112 | ||
113 | template <> | |
114 | struct drop_front_impl<ext::std::integer_sequence_tag> { | |
115 | template <std::size_t n, typename T, T ...t, std::size_t ...i> | |
116 | static constexpr auto drop_front_helper(std::integer_sequence<T, t...>, | |
117 | std::index_sequence<i...>) | |
118 | { | |
119 | constexpr T ts[sizeof...(t)+1] = {t...}; // avoid 0-sized array | |
120 | return std::integer_sequence<T, ts[n + i]...>{}; | |
121 | } | |
122 | ||
123 | template <typename T, T ...t, typename N> | |
124 | static constexpr auto apply(std::integer_sequence<T, t...> ts, N const&) { | |
125 | constexpr std::size_t n = N::value; | |
126 | constexpr std::size_t len = sizeof...(t); | |
127 | return drop_front_helper<n>(ts, | |
128 | std::make_index_sequence<(n < len ? len - n : 0)>{}); | |
129 | } | |
130 | }; | |
131 | ||
132 | template <> | |
133 | struct is_empty_impl<ext::std::integer_sequence_tag> { | |
134 | template <typename T, T ...xs> | |
135 | static constexpr auto apply(std::integer_sequence<T, xs...> const&) | |
136 | { return hana::bool_c<sizeof...(xs) == 0>; } | |
137 | }; | |
138 | BOOST_HANA_NAMESPACE_END | |
139 | ||
140 | #endif // !BOOST_HANA_EXT_STD_INTEGER_SEQUENCE_HPP |