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/*!
@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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