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1 | /*! | |
2 | @file | |
3 | Defines `boost::hana::less`. | |
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_LESS_HPP | |
11 | #define BOOST_HANA_LESS_HPP | |
12 | ||
13 | #include <boost/hana/fwd/less.hpp> | |
14 | ||
15 | #include <boost/hana/and.hpp> | |
16 | #include <boost/hana/bool.hpp> | |
17 | #include <boost/hana/concept/constant.hpp> | |
18 | #include <boost/hana/concept/orderable.hpp> | |
19 | #include <boost/hana/concept/product.hpp> | |
20 | #include <boost/hana/concept/sequence.hpp> | |
21 | #include <boost/hana/config.hpp> | |
22 | #include <boost/hana/core/common.hpp> | |
23 | #include <boost/hana/core/to.hpp> | |
24 | #include <boost/hana/core/dispatch.hpp> | |
25 | #include <boost/hana/detail/concepts.hpp> | |
26 | #include <boost/hana/detail/has_common_embedding.hpp> | |
27 | #include <boost/hana/detail/nested_than.hpp> // required by fwd decl | |
28 | #include <boost/hana/equal.hpp> | |
29 | #include <boost/hana/first.hpp> | |
30 | #include <boost/hana/if.hpp> | |
31 | #include <boost/hana/less_equal.hpp> | |
32 | #include <boost/hana/lexicographical_compare.hpp> | |
33 | #include <boost/hana/or.hpp> | |
34 | #include <boost/hana/second.hpp> | |
35 | #include <boost/hana/value.hpp> | |
36 | ||
37 | ||
38 | BOOST_HANA_NAMESPACE_BEGIN | |
39 | //! @cond | |
40 | template <typename X, typename Y> | |
41 | constexpr auto less_t::operator()(X&& x, Y&& y) const { | |
42 | using T = typename hana::tag_of<X>::type; | |
43 | using U = typename hana::tag_of<Y>::type; | |
44 | using Less = BOOST_HANA_DISPATCH_IF(decltype(less_impl<T, U>{}), | |
45 | hana::Orderable<T>::value && | |
46 | hana::Orderable<U>::value && | |
47 | !is_default<less_impl<T, U>>::value | |
48 | ); | |
49 | ||
50 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
51 | static_assert(hana::Orderable<T>::value, | |
52 | "hana::less(x, y) requires 'x' to be Orderable"); | |
53 | ||
54 | static_assert(hana::Orderable<U>::value, | |
55 | "hana::less(x, y) requires 'y' to be Orderable"); | |
56 | ||
57 | static_assert(!is_default<less_impl<T, U>>::value, | |
58 | "hana::less(x, y) requires 'x' and 'y' to be embeddable " | |
59 | "in a common Orderable"); | |
60 | #endif | |
61 | ||
62 | return Less::apply(static_cast<X&&>(x), static_cast<Y&&>(y)); | |
63 | } | |
64 | //! @endcond | |
65 | ||
66 | template <typename T, typename U, bool condition> | |
67 | struct less_impl<T, U, when<condition>> : default_ { | |
68 | template <typename ...Args> | |
69 | static constexpr auto apply(Args&& ...) = delete; | |
70 | }; | |
71 | ||
72 | // Cross-type overload | |
73 | template <typename T, typename U> | |
74 | struct less_impl<T, U, when< | |
75 | detail::has_nontrivial_common_embedding<Orderable, T, U>::value && | |
76 | !detail::LessThanComparable<T, U>::value | |
77 | >> { | |
78 | using C = typename hana::common<T, U>::type; | |
79 | template <typename X, typename Y> | |
80 | static constexpr decltype(auto) apply(X&& x, Y&& y) { | |
81 | return hana::less(hana::to<C>(static_cast<X&&>(x)), | |
82 | hana::to<C>(static_cast<Y&&>(y))); | |
83 | } | |
84 | }; | |
85 | ||
86 | ////////////////////////////////////////////////////////////////////////// | |
87 | // Model for LessThanComparable data types | |
88 | ////////////////////////////////////////////////////////////////////////// | |
89 | template <typename T, typename U> | |
90 | struct less_impl<T, U, when<detail::LessThanComparable<T, U>::value>> { | |
91 | template <typename X, typename Y> | |
92 | static constexpr decltype(auto) apply(X&& x, Y&& y) | |
93 | { return static_cast<X&&>(x) < static_cast<Y&&>(y); } | |
94 | }; | |
95 | ||
96 | ////////////////////////////////////////////////////////////////////////// | |
97 | // Model for Constants wrapping an Orderable | |
98 | ////////////////////////////////////////////////////////////////////////// | |
99 | template <typename C> | |
100 | struct less_impl<C, C, when< | |
101 | hana::Constant<C>::value && | |
102 | Orderable<typename C::value_type>::value | |
103 | >> { | |
104 | template <typename X, typename Y> | |
105 | static constexpr auto apply(X const&, Y const&) { | |
106 | constexpr auto less = hana::less(hana::value<X>(), hana::value<Y>()); | |
107 | constexpr bool truth_value = hana::if_(less, true, false); | |
108 | return hana::bool_c<truth_value>; | |
109 | } | |
110 | }; | |
111 | ||
112 | ////////////////////////////////////////////////////////////////////////// | |
113 | // Model for Products | |
114 | ////////////////////////////////////////////////////////////////////////// | |
115 | template <typename T, typename U> | |
116 | struct less_impl<T, U, when<hana::Product<T>::value && hana::Product<U>::value>> { | |
117 | template <typename X, typename Y> | |
118 | static constexpr decltype(auto) apply(X const& x, Y const& y) { | |
119 | return hana::or_( | |
120 | hana::less(hana::first(x), hana::first(y)), | |
121 | hana::and_( | |
122 | hana::less_equal(hana::first(x), hana::first(y)), | |
123 | hana::less(hana::second(x), hana::second(y)) | |
124 | ) | |
125 | ); | |
126 | } | |
127 | }; | |
128 | ||
129 | ////////////////////////////////////////////////////////////////////////// | |
130 | // Model for Sequences | |
131 | ////////////////////////////////////////////////////////////////////////// | |
132 | template <typename T, typename U> | |
133 | struct less_impl<T, U, when< | |
134 | hana::Sequence<T>::value && hana::Sequence<U>::value | |
135 | >> { | |
136 | template <typename Xs, typename Ys> | |
137 | static constexpr auto apply(Xs const& xs, Ys const& ys) | |
138 | { return hana::lexicographical_compare(xs, ys); } | |
139 | }; | |
140 | BOOST_HANA_NAMESPACE_END | |
141 | ||
142 | #endif // !BOOST_HANA_LESS_HPP |