77 lines
2.6 KiB
C++
77 lines
2.6 KiB
C++
/*!
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@file
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Defines `boost::hana::intersperse`.
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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_INTERSPERSE_HPP
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#define BOOST_HANA_INTERSPERSE_HPP
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#include <boost/hana/fwd/intersperse.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/bool.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 <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename Z>
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constexpr auto intersperse_t::operator()(Xs&& xs, Z&& z) const {
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using S = typename hana::tag_of<Xs>::type;
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using Intersperse = BOOST_HANA_DISPATCH_IF(intersperse_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::intersperse(xs, z) requires 'xs' to be a Sequence");
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#endif
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return Intersperse::apply(static_cast<Xs&&>(xs), static_cast<Z&&>(z));
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}
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//! @endcond
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template <typename S, bool condition>
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struct intersperse_impl<S, when<condition>> : default_ {
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template <std::size_t i, typename Xs, typename Z>
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static constexpr decltype(auto)
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pick(Xs&&, Z&& z, hana::false_ /* odd index */)
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{ return static_cast<Z&&>(z); }
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template <std::size_t i, typename Xs, typename Z>
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static constexpr decltype(auto)
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pick(Xs&& xs, Z&&, hana::true_ /* even index */)
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{ return hana::at_c<(i + 1) / 2>(static_cast<Xs&&>(xs)); }
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template <typename Xs, typename Z, std::size_t ...i>
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static constexpr auto
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intersperse_helper(Xs&& xs, Z&& z, std::index_sequence<i...>) {
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return hana::make<S>(
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pick<i>(static_cast<Xs&&>(xs), static_cast<Z&&>(z),
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hana::bool_c<(i % 2 == 0)>)...
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);
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}
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template <typename Xs, typename Z>
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static constexpr auto apply(Xs&& xs, Z&& z) {
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constexpr std::size_t size = decltype(hana::length(xs))::value;
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constexpr std::size_t new_size = size == 0 ? 0 : (size * 2) - 1;
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return intersperse_helper(static_cast<Xs&&>(xs), static_cast<Z&&>(z),
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std::make_index_sequence<new_size>{});
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_INTERSPERSE_HPP
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