81 lines
2.7 KiB
C++
81 lines
2.7 KiB
C++
/*!
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@file
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Defines `boost::hana::concat`.
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@copyright Louis Dionne 2013-2016
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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_CONCAT_HPP
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#define BOOST_HANA_CONCAT_HPP
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#include <boost/hana/fwd/concat.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/monad_plus.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/length.hpp>
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#include <cstddef>
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#include <type_traits>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename Ys>
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constexpr auto concat_t::operator()(Xs&& xs, Ys&& ys) const {
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using M = typename hana::tag_of<Xs>::type;
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using Concat = BOOST_HANA_DISPATCH_IF(concat_impl<M>,
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hana::MonadPlus<M>::value &&
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std::is_same<typename hana::tag_of<Ys>::type, M>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(std::is_same<typename hana::tag_of<Ys>::type, M>::value,
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"hana::concat(xs, ys) requires 'xs' and 'ys' to have the same tag");
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static_assert(hana::MonadPlus<M>::value,
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"hana::concat(xs, ys) requires 'xs' and 'ys' to be MonadPlus");
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#endif
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return Concat::apply(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys));
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}
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//! @endcond
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template <typename M, bool condition>
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struct concat_impl<M, when<condition>> : default_ {
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template <typename ...Args>
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static constexpr auto apply(Args&& ...) = delete;
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};
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template <typename S>
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struct concat_impl<S, when<Sequence<S>::value>> {
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template <typename Xs, typename Ys, std::size_t ...xi, std::size_t ...yi>
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static constexpr auto
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concat_helper(Xs&& xs, Ys&& ys, std::index_sequence<xi...>,
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std::index_sequence<yi...>)
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{
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return hana::make<S>(
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hana::at_c<xi>(static_cast<Xs&&>(xs))...,
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hana::at_c<yi>(static_cast<Ys&&>(ys))...
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);
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}
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template <typename Xs, typename Ys>
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static constexpr auto apply(Xs&& xs, Ys&& ys) {
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constexpr std::size_t xi = decltype(hana::length(xs))::value;
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constexpr std::size_t yi = decltype(hana::length(ys))::value;
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return concat_helper(static_cast<Xs&&>(xs), static_cast<Ys&&>(ys),
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std::make_index_sequence<xi>{},
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std::make_index_sequence<yi>{});
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_CONCAT_HPP
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