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 Hu Chunming
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/*!
@file
Defines `boost::hana::lexicographical_compare`.
Copyright Louis Dionne 2013-2022
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>
namespace boost { namespace hana {
//! @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
>);
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_LEXICOGRAPHICAL_COMPARE_HPP
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