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Editing: less.hpp
/*! @file Defines `boost::hana::less`. @copyright Louis Dionne 2013-2017 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_LESS_HPP #define BOOST_HANA_LESS_HPP #include <boost/hana/fwd/less.hpp> #include <boost/hana/and.hpp> #include <boost/hana/bool.hpp> #include <boost/hana/concept/constant.hpp> #include <boost/hana/concept/orderable.hpp> #include <boost/hana/concept/product.hpp> #include <boost/hana/concept/sequence.hpp> #include <boost/hana/config.hpp> #include <boost/hana/core/common.hpp> #include <boost/hana/core/to.hpp> #include <boost/hana/core/dispatch.hpp> #include <boost/hana/detail/concepts.hpp> #include <boost/hana/detail/has_common_embedding.hpp> #include <boost/hana/detail/nested_than.hpp> // required by fwd decl #include <boost/hana/equal.hpp> #include <boost/hana/first.hpp> #include <boost/hana/if.hpp> #include <boost/hana/less_equal.hpp> #include <boost/hana/lexicographical_compare.hpp> #include <boost/hana/or.hpp> #include <boost/hana/second.hpp> #include <boost/hana/value.hpp> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename X, typename Y> constexpr auto less_t::operator()(X&& x, Y&& y) const { using T = typename hana::tag_of<X>::type; using U = typename hana::tag_of<Y>::type; using Less = BOOST_HANA_DISPATCH_IF(decltype(less_impl<T, U>{}), hana::Orderable<T>::value && hana::Orderable<U>::value && !is_default<less_impl<T, U>>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Orderable<T>::value, "hana::less(x, y) requires 'x' to be Orderable"); static_assert(hana::Orderable<U>::value, "hana::less(x, y) requires 'y' to be Orderable"); static_assert(!is_default<less_impl<T, U>>::value, "hana::less(x, y) requires 'x' and 'y' to be embeddable " "in a common Orderable"); #endif return Less::apply(static_cast<X&&>(x), static_cast<Y&&>(y)); } //! @endcond template <typename T, typename U, bool condition> struct less_impl<T, U, when<condition>> : default_ { template <typename ...Args> static constexpr auto apply(Args&& ...) = delete; }; // Cross-type overload template <typename T, typename U> struct less_impl<T, U, when< detail::has_nontrivial_common_embedding<Orderable, T, U>::value && !detail::LessThanComparable<T, U>::value >> { using C = typename hana::common<T, U>::type; template <typename X, typename Y> static constexpr decltype(auto) apply(X&& x, Y&& y) { return hana::less(hana::to<C>(static_cast<X&&>(x)), hana::to<C>(static_cast<Y&&>(y))); } }; ////////////////////////////////////////////////////////////////////////// // Model for LessThanComparable data types ////////////////////////////////////////////////////////////////////////// template <typename T, typename U> struct less_impl<T, U, when<detail::LessThanComparable<T, U>::value>> { template <typename X, typename Y> static constexpr decltype(auto) apply(X&& x, Y&& y) { return static_cast<X&&>(x) < static_cast<Y&&>(y); } }; ////////////////////////////////////////////////////////////////////////// // Model for Constants wrapping an Orderable ////////////////////////////////////////////////////////////////////////// template <typename C> struct less_impl<C, C, when< hana::Constant<C>::value && Orderable<typename C::value_type>::value >> { template <typename X, typename Y> static constexpr auto apply(X const&, Y const&) { constexpr auto is_less = hana::less(hana::value<X>(), hana::value<Y>()); constexpr bool truth_value = hana::if_(is_less, true, false); return hana::bool_c<truth_value>; } }; ////////////////////////////////////////////////////////////////////////// // Model for Products ////////////////////////////////////////////////////////////////////////// template <typename T, typename U> struct less_impl<T, U, when<hana::Product<T>::value && hana::Product<U>::value>> { template <typename X, typename Y> static constexpr decltype(auto) apply(X const& x, Y const& y) { return hana::or_( hana::less(hana::first(x), hana::first(y)), hana::and_( hana::less_equal(hana::first(x), hana::first(y)), hana::less(hana::second(x), hana::second(y)) ) ); } }; ////////////////////////////////////////////////////////////////////////// // Model for Sequences ////////////////////////////////////////////////////////////////////////// template <typename T, typename U> struct less_impl<T, U, when< hana::Sequence<T>::value && hana::Sequence<U>::value >> { template <typename Xs, typename Ys> static constexpr auto apply(Xs const& xs, Ys const& ys) { return hana::lexicographical_compare(xs, ys); } }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_LESS_HPP
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