ceph/src/boost/libs/hana/include/boost/hana/minimum.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::minimum`.
   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_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>
  27     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>
  42     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>
  67             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>
  78         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>
  92         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