boost/hana/lexicographical_compare.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::lexicographical_compare`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP
0011 #define BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP
0012
0013 #include <boost/hana/fwd/lexicographical_compare.hpp>
0014
0015 #include <boost/hana/bool.hpp>
0016 #include <boost/hana/concept/iterable.hpp>
0017 #include <boost/hana/config.hpp>
0018 #include <boost/hana/core/dispatch.hpp>
0019 #include <boost/hana/drop_front.hpp>
0020 #include <boost/hana/front.hpp>
0021 #include <boost/hana/if.hpp>
0022 #include <boost/hana/is_empty.hpp>
0023 #include <boost/hana/less.hpp>
0024
0025
0026 namespace boost { namespace hana {
0027     //! @cond
0028     template <typename Xs, typename Ys>
0029     constexpr auto lexicographical_compare_t::operator()(Xs const& xs, Ys const& ys) const {
0030         return hana::lexicographical_compare(xs, ys, hana::less);
0031     }
0032
0033     template <typename Xs, typename Ys, typename Pred>
0034     constexpr auto lexicographical_compare_t::operator()(Xs const& xs, Ys const& ys, Pred const& pred) const {
0035         using It1 = typename hana::tag_of<Xs>::type;
0036         using It2 = typename hana::tag_of<Ys>::type;
0037         using LexicographicalCompare = BOOST_HANA_DISPATCH_IF(
0038             lexicographical_compare_impl<It1>,
0039             hana::Iterable<It1>::value &&
0040             hana::Iterable<It2>::value
0041         );
0042
0043     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0044         static_assert(hana::Iterable<It1>::value,
0045         "hana::lexicographical_compare(xs, ys, pred) requires 'xs' to be Iterable");
0046
0047         static_assert(hana::Iterable<It2>::value,
0048         "hana::lexicographical_compare(xs, ys, pred) requires 'ys' to be Iterable");
0049     #endif
0050
0051         return LexicographicalCompare::apply(xs, ys, pred);
0052     }
0053     //! @endcond
0054
0055     template <typename It, bool condition>
0056     struct lexicographical_compare_impl<It, when<condition>> : default_ {
0057         template <typename Xs, typename Ys, typename Pred>
0058         static constexpr auto
0059         helper2(Xs const&, Ys const&, Pred const&, hana::true_)
0060         { return hana::false_c; }
0061
0062         template <typename Xs, typename Ys, typename Pred>
0063         static constexpr auto
0064         helper2(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_)
0065         { return apply(hana::drop_front(xs), hana::drop_front(ys), pred); }
0066
0067         template <typename Xs, typename Ys, typename Pred>
0068         static constexpr auto
0069         helper2(Xs const& xs, Ys const& ys, Pred const& pred, bool is_greater)
0070         { return is_greater ? false : apply(hana::drop_front(xs), hana::drop_front(ys), pred); }
0071
0072
0073         template <typename Xs, typename Ys, typename Pred>
0074         static constexpr auto
0075         helper1(Xs const&, Ys const&, Pred const&, hana::true_)
0076         { return hana::true_c; }
0077
0078         template <typename Xs, typename Ys, typename Pred>
0079         static constexpr auto
0080         helper1(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_)
0081         { return helper2(xs, ys, pred, hana::if_(pred(hana::front(ys), hana::front(xs)), hana::true_c, hana::false_c)); }
0082
0083         template <typename Xs, typename Ys, typename Pred>
0084         static constexpr auto
0085         helper1(Xs const& xs, Ys const& ys, Pred const& pred, bool is_less)
0086         { return is_less ? true : helper2(xs, ys, pred, hana::if_(pred(hana::front(ys), hana::front(xs)), hana::true_c, hana::false_c)); }
0087
0088
0089         template <typename Xs, typename Ys, typename Pred>
0090         static constexpr auto
0091         helper(Xs const&, Ys const& ys, Pred const&, hana::true_)
0092         { return hana::not_(hana::is_empty(ys)); }
0093
0094         template <typename Xs, typename Ys, typename Pred>
0095         static constexpr auto
0096         helper(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_)
0097         { return helper1(xs, ys, pred, hana::if_(pred(hana::front(xs), hana::front(ys)), hana::true_c, hana::false_c)); }
0098
0099
0100         template <typename Xs, typename Ys, typename Pred>
0101         static constexpr auto apply(Xs const& xs, Ys const& ys, Pred const& pred) {
0102             return helper(xs, ys, pred, hana::bool_c<
0103                 decltype(hana::is_empty(xs))::value ||
0104                 decltype(hana::is_empty(ys))::value
0105             >);
0106         }
0107     };
0108 }} // end namespace boost::hana
0109
0110 #endif // !BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP