/*!
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@file
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Defines `boost::hana::sort`.
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@copyright Louis Dionne 2013-2017
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_SORT_HPP
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#define BOOST_HANA_SORT_HPP
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#include <boost/hana/fwd/sort.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/sequence.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/core/make.hpp>
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#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
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#include <boost/hana/length.hpp>
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#include <boost/hana/less.hpp>
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#include <utility> // std::declval, std::index_sequence
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename Predicate>
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constexpr auto sort_t::operator()(Xs&& xs, Predicate&& pred) const {
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using S = typename hana::tag_of<Xs>::type;
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using Sort = BOOST_HANA_DISPATCH_IF(sort_impl<S>,
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hana::Sequence<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::sort(xs, predicate) requires 'xs' to be a Sequence");
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#endif
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return Sort::apply(static_cast<Xs&&>(xs),
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static_cast<Predicate&&>(pred));
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}
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template <typename Xs>
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constexpr auto sort_t::operator()(Xs&& xs) const {
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using S = typename hana::tag_of<Xs>::type;
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using Sort = BOOST_HANA_DISPATCH_IF(sort_impl<S>,
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hana::Sequence<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::sort(xs) requires 'xs' to be a Sequence");
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#endif
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return Sort::apply(static_cast<Xs&&>(xs));
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}
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//! @endcond
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namespace detail {
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template <typename Xs, typename Pred>
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struct sort_predicate {
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template <std::size_t I, std::size_t J>
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using apply = decltype(std::declval<Pred>()(
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hana::at_c<I>(std::declval<Xs>()),
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hana::at_c<J>(std::declval<Xs>())
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));
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};
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template <typename Left, typename Right>
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struct concat;
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template <std::size_t ...l, std::size_t ...r>
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struct concat<std::index_sequence<l...>, std::index_sequence<r...>> {
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using type = std::index_sequence<l..., r...>;
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};
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template <typename Pred, bool PickRight, typename Left, typename Right>
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struct merge;
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template <
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typename Pred,
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std::size_t l0,
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std::size_t l1,
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std::size_t ...l,
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std::size_t r0,
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std::size_t ...r>
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struct merge<
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Pred,
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false,
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std::index_sequence<l0, l1, l...>,
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std::index_sequence<r0, r...>
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> {
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using type = typename concat<
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std::index_sequence<l0>,
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typename merge<
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Pred,
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(bool)Pred::template apply<r0, l1>::value,
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std::index_sequence<l1, l...>,
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std::index_sequence<r0, r...>
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>::type
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>::type;
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};
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template <
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typename Pred,
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std::size_t l0,
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std::size_t r0,
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std::size_t ...r>
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struct merge<
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Pred,
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false,
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std::index_sequence<l0>,
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std::index_sequence<r0, r...>
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> {
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using type = std::index_sequence<l0, r0, r...>;
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};
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template <
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typename Pred,
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std::size_t l0,
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std::size_t ...l,
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std::size_t r0,
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std::size_t r1,
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std::size_t ...r>
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struct merge<
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Pred,
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true,
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std::index_sequence<l0, l...>,
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std::index_sequence<r0, r1, r...>
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> {
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using type = typename concat<
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std::index_sequence<r0>,
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typename merge<
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Pred,
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(bool)Pred::template apply<r1, l0>::value,
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std::index_sequence<l0, l...>,
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std::index_sequence<r1, r...>
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>::type
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>::type;
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};
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template <
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typename Pred,
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std::size_t l0,
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std::size_t ...l,
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std::size_t r0>
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struct merge<
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Pred,
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true,
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std::index_sequence<l0, l...>,
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std::index_sequence<r0>
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> {
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using type = std::index_sequence<r0, l0, l...>;
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};
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template <typename Pred, typename Left, typename Right>
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struct merge_helper;
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template <
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typename Pred,
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std::size_t l0,
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std::size_t ...l,
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std::size_t r0,
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std::size_t ...r>
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struct merge_helper<
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Pred,
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std::index_sequence<l0, l...>,
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std::index_sequence<r0, r...>
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> {
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using type = typename merge<
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Pred,
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(bool)Pred::template apply<r0, l0>::value,
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std::index_sequence<l0, l...>,
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std::index_sequence<r0, r...>
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>::type;
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};
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// split templated structure, Nr represents the number of elements
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// from Right to move to Left
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// There are two specializations:
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// The first handles the generic case (Nr > 0)
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// The second handles the stop condition (Nr == 0)
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// These two specializations are not strictly ordered as
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// the first cannot match Nr==0 && empty Right
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// the second cannot match Nr!=0
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// std::enable_if<Nr!=0> is therefore required to make sure these two
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// specializations will never both be candidates during an overload
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// resolution (otherwise ambiguity occurs for Nr==0 and non-empty Right)
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template <std::size_t Nr, typename Left, typename Right, typename=void>
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struct split;
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template <
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std::size_t Nr,
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std::size_t ...l,
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std::size_t ...r,
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std::size_t r0>
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struct split<
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Nr,
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std::index_sequence<l...>,
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std::index_sequence<r0, r...>,
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typename std::enable_if<Nr!=0>::type
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> {
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using sp = split<
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Nr-1,
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std::index_sequence<l..., r0>,
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std::index_sequence<r...>
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>;
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using left = typename sp::left;
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using right = typename sp::right;
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};
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template <std::size_t ...l, std::size_t ...r>
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struct split<0, std::index_sequence<l...>, std::index_sequence<r...>> {
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using left = std::index_sequence<l...>;
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using right = std::index_sequence<r...>;
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};
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template <typename Pred, typename Sequence>
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struct merge_sort_impl;
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template <typename Pred, std::size_t ...seq>
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struct merge_sort_impl<Pred, std::index_sequence<seq...>> {
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using sequence = std::index_sequence<seq...>;
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using sp = split<
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sequence::size() / 2,
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std::index_sequence<>,
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sequence
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>;
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using type = typename merge_helper<
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Pred,
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typename merge_sort_impl<Pred, typename sp::left>::type,
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typename merge_sort_impl<Pred, typename sp::right>::type
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>::type;
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};
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template <typename Pred, std::size_t x>
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struct merge_sort_impl<Pred, std::index_sequence<x>> {
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using type = std::index_sequence<x>;
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};
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template <typename Pred>
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struct merge_sort_impl<Pred, std::index_sequence<>> {
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using type = std::index_sequence<>;
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};
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} // end namespace detail
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template <typename S, bool condition>
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struct sort_impl<S, when<condition>> : default_ {
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template <typename Xs, std::size_t ...i>
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static constexpr auto apply_impl(Xs&& xs, std::index_sequence<i...>) {
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return hana::make<S>(hana::at_c<i>(static_cast<Xs&&>(xs))...);
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}
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template <typename Xs, typename Pred>
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static constexpr auto apply(Xs&& xs, Pred const&) {
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constexpr std::size_t Len = decltype(hana::length(xs))::value;
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using Indices = typename detail::merge_sort_impl<
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detail::sort_predicate<Xs&&, Pred>,
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std::make_index_sequence<Len>
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>::type;
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return apply_impl(static_cast<Xs&&>(xs), Indices{});
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}
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template <typename Xs>
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static constexpr auto apply(Xs&& xs)
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{ return sort_impl::apply(static_cast<Xs&&>(xs), hana::less); }
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_SORT_HPP
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