1 /*!
2 @file
3 Defines `boost::hana::minimum`.
4 
5 @copyright Louis Dionne 2013-2017
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_MINIMUM_HPP
11 #define BOOST_HANA_MINIMUM_HPP
12 
13 #include <boost/hana/fwd/minimum.hpp>
14 
15 #include <boost/hana/concept/foldable.hpp>
16 #include <boost/hana/config.hpp>
17 #include <boost/hana/core/dispatch.hpp>
18 #include <boost/hana/detail/nested_by.hpp> // required by fwd decl
19 #include <boost/hana/fold_left.hpp>
20 #include <boost/hana/if.hpp>
21 #include <boost/hana/less.hpp>
22 
23 
24 BOOST_HANA_NAMESPACE_BEGIN
25     //! @cond
26     template <typename Xs>
operator ()(Xs && xs) const27     constexpr decltype(auto) minimum_t::operator()(Xs&& xs) const {
28         using S = typename hana::tag_of<Xs>::type;
29         using Minimum = BOOST_HANA_DISPATCH_IF(minimum_impl<S>,
30             hana::Foldable<S>::value
31         );
32 
33     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
34         static_assert(hana::Foldable<S>::value,
35         "hana::minimum(xs) requires 'xs' to be Foldable");
36     #endif
37 
38         return Minimum::apply(static_cast<Xs&&>(xs));
39     }
40 
41     template <typename Xs, typename Predicate>
operator ()(Xs && xs,Predicate && pred) const42     constexpr decltype(auto) minimum_t::operator()(Xs&& xs, Predicate&& pred) const {
43         using S = typename hana::tag_of<Xs>::type;
44         using Minimum = BOOST_HANA_DISPATCH_IF(minimum_pred_impl<S>,
45             hana::Foldable<S>::value
46         );
47 
48     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
49         static_assert(hana::Foldable<S>::value,
50         "hana::minimum(xs, predicate) requires 'xs' to be Foldable");
51     #endif
52 
53         return Minimum::apply(static_cast<Xs&&>(xs),
54                               static_cast<Predicate&&>(pred));
55     }
56     //! @endcond
57 
58     //////////////////////////////////////////////////////////////////////////
59     // minimum (with a custom predicate)
60     //////////////////////////////////////////////////////////////////////////
61     namespace detail {
62         template <typename Pred>
63         struct min_by {
64             Pred pred;
65 
66             template <typename X, typename Y>
operator ()detail::min_by67             constexpr decltype(auto) operator()(X&& x, Y&& y) const {
68                 auto result = (*pred)(x, y);
69                 return hana::if_(result, static_cast<X&&>(x),
70                                          static_cast<Y&&>(y));
71             }
72         };
73     }
74 
75     template <typename T, bool condition>
76     struct minimum_pred_impl<T, when<condition>> : default_ {
77         template <typename Xs, typename Pred>
applyminimum_pred_impl78         static constexpr decltype(auto) apply(Xs&& xs, Pred const& pred) {
79             // We use a pointer instead of a reference to avoid a Clang ICE.
80             return hana::fold_left(static_cast<Xs&&>(xs),
81                 detail::min_by<decltype(&pred)>{&pred}
82             );
83         }
84     };
85 
86     //////////////////////////////////////////////////////////////////////////
87     // minimum (without a custom predicate)
88     //////////////////////////////////////////////////////////////////////////
89     template <typename T, bool condition>
90     struct minimum_impl<T, when<condition>> : default_ {
91         template <typename Xs>
applyminimum_impl92         static constexpr decltype(auto) apply(Xs&& xs)
93         { return hana::minimum(static_cast<Xs&&>(xs), hana::less); }
94     };
95 BOOST_HANA_NAMESPACE_END
96 
97 #endif // !BOOST_HANA_MINIMUM_HPP
98