/*! @file Defines `boost::hana::lexicographical_compare`. @copyright Louis Dionne 2013-2016 Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) */ #ifndef BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP #define BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP #include <boost/hana/fwd/lexicographical_compare.hpp> #include <boost/hana/bool.hpp> #include <boost/hana/concept/iterable.hpp> #include <boost/hana/config.hpp> #include <boost/hana/core/dispatch.hpp> #include <boost/hana/drop_front.hpp> #include <boost/hana/front.hpp> #include <boost/hana/if.hpp> #include <boost/hana/is_empty.hpp> #include <boost/hana/less.hpp> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename Xs, typename Ys> constexpr auto lexicographical_compare_t::operator()(Xs const& xs, Ys const& ys) const { return hana::lexicographical_compare(xs, ys, hana::less); } template <typename Xs, typename Ys, typename Pred> constexpr auto lexicographical_compare_t::operator()(Xs const& xs, Ys const& ys, Pred const& pred) const { using It1 = typename hana::tag_of<Xs>::type; using It2 = typename hana::tag_of<Ys>::type; using LexicographicalCompare = BOOST_HANA_DISPATCH_IF( lexicographical_compare_impl<It1>, hana::Iterable<It1>::value && hana::Iterable<It2>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Iterable<It1>::value, "hana::lexicographical_compare(xs, ys, pred) requires 'xs' to be Iterable"); static_assert(hana::Iterable<It2>::value, "hana::lexicographical_compare(xs, ys, pred) requires 'ys' to be Iterable"); #endif return LexicographicalCompare::apply(xs, ys, pred); } //! @endcond template <typename It, bool condition> struct lexicographical_compare_impl<It, when<condition>> : default_ { template <typename Xs, typename Ys, typename Pred> static constexpr auto helper2(Xs const&, Ys const&, Pred const&, hana::true_) { return hana::false_c; } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper2(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_) { return apply(hana::drop_front(xs), hana::drop_front(ys), pred); } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper2(Xs const& xs, Ys const& ys, Pred const& pred, bool is_greater) { return is_greater ? false : apply(hana::drop_front(xs), hana::drop_front(ys), pred); } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper1(Xs const&, Ys const&, Pred const&, hana::true_) { return hana::true_c; } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper1(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_) { return helper2(xs, ys, pred, hana::if_(pred(hana::front(ys), hana::front(xs)), hana::true_c, hana::false_c)); } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper1(Xs const& xs, Ys const& ys, Pred const& pred, bool is_less) { return is_less ? true : helper2(xs, ys, pred, hana::if_(pred(hana::front(ys), hana::front(xs)), hana::true_c, hana::false_c)); } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper(Xs const&, Ys const& ys, Pred const&, hana::true_) { return hana::not_(hana::is_empty(ys)); } template <typename Xs, typename Ys, typename Pred> static constexpr auto helper(Xs const& xs, Ys const& ys, Pred const& pred, hana::false_) { return helper1(xs, ys, pred, hana::if_(pred(hana::front(xs), hana::front(ys)), hana::true_c, hana::false_c)); } template <typename Xs, typename Ys, typename Pred> static constexpr auto apply(Xs const& xs, Ys const& ys, Pred const& pred) { return helper(xs, ys, pred, hana::bool_c< decltype(hana::is_empty(xs))::value || decltype(hana::is_empty(ys))::value >); } }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP