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+/*!
+@file
+Defines `boost::hana::unpack`.
+
+@copyright Louis Dionne 2013-2016
+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_UNPACK_HPP
+#define BOOST_HANA_UNPACK_HPP
+
+#include <boost/hana/fwd/unpack.hpp>
+
+#include <boost/hana/accessors.hpp>
+#include <boost/hana/at.hpp>
+#include <boost/hana/concept/foldable.hpp>
+#include <boost/hana/concept/iterable.hpp>
+#include <boost/hana/concept/struct.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/first.hpp>
+#include <boost/hana/functional/partial.hpp>
+#include <boost/hana/fwd/fold_left.hpp>
+#include <boost/hana/length.hpp>
+#include <boost/hana/pair.hpp>
+#include <boost/hana/second.hpp>
+
+#include <cstddef>
+#include <utility>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! @cond
+ template <typename Xs, typename F>
+ constexpr decltype(auto) unpack_t::operator()(Xs&& xs, F&& f) const {
+ using S = typename hana::tag_of<Xs>::type;
+ using Unpack = BOOST_HANA_DISPATCH_IF(unpack_impl<S>,
+ hana::Foldable<S>::value
+ );
+
+ #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+ static_assert(hana::Foldable<S>::value,
+ "hana::unpack(xs, f) requires 'xs' to be Foldable");
+ #endif
+
+ return Unpack::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f));
+ }
+ //! @endcond
+
+ template <typename T, bool condition>
+ struct unpack_impl<T, when<condition>> : default_ {
+ template <typename Xs, typename F>
+ static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
+ return hana::fold_left(static_cast<Xs&&>(xs),
+ static_cast<F&&>(f),
+ hana::partial)();
+ }
+ };
+
+ template <typename It>
+ struct unpack_impl<It, when<
+ hana::Iterable<It>::value && !is_default<length_impl<It>>::value
+ >> {
+ template <typename Xs, typename F, std::size_t ...i>
+ static constexpr decltype(auto)
+ unpack_helper(Xs&& xs, F&& f, std::index_sequence<i...>) {
+ return static_cast<F&&>(f)(hana::at_c<i>(static_cast<Xs&&>(xs))...);
+ }
+
+ template <typename Xs, typename F>
+ static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
+ constexpr std::size_t N = decltype(hana::length(xs))::value;
+ return unpack_helper(static_cast<Xs&&>(xs), static_cast<F&&>(f),
+ std::make_index_sequence<N>{});
+ }
+ };
+
+ template <typename T, std::size_t N>
+ struct unpack_impl<T[N]> {
+ template <typename Xs, typename F, std::size_t ...i>
+ static constexpr decltype(auto)
+ unpack_helper(Xs&& xs, F&& f, std::index_sequence<i...>) {
+ return static_cast<F&&>(f)(static_cast<Xs&&>(xs)[i]...);
+ }
+
+ template <typename Xs, typename F>
+ static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
+ return unpack_impl::unpack_helper(static_cast<Xs&&>(xs),
+ static_cast<F&&>(f),
+ std::make_index_sequence<N>{});
+ }
+ };
+
+ //////////////////////////////////////////////////////////////////////////
+ // Model for Products
+ //////////////////////////////////////////////////////////////////////////
+ template <typename T>
+ struct unpack_impl<T, when<hana::Product<T>::value>> {
+ template <typename P, typename F>
+ static constexpr decltype(auto) apply(P&& p, F&& f) {
+ return static_cast<F&&>(f)(
+ hana::first(static_cast<P&&>(p)),
+ hana::second(static_cast<P&&>(p))
+ );
+ }
+ };
+
+ //////////////////////////////////////////////////////////////////////////
+ // Model for Structs
+ //////////////////////////////////////////////////////////////////////////
+ namespace struct_detail {
+ // This is equivalent to `demux`, except that `demux` can't forward
+ // the `udt` because it does not know the `g`s are accessors. Hence,
+ // this can result in faster code.
+ struct almost_demux {
+ template <typename F, typename Udt, typename ...Members>
+ constexpr decltype(auto)
+ operator()(F&& f, Udt&& udt, Members&& ...g) const {
+ return static_cast<F&&>(f)(hana::make_pair(
+ hana::first(static_cast<Members&&>(g)),
+ hana::second(static_cast<Members&&>(g))
+ (static_cast<Udt&&>(udt))
+ )...);
+ }
+ };
+ }
+
+ template <typename S>
+ struct unpack_impl<S, when<hana::Struct<S>::value>> {
+ template <typename Udt, typename F>
+ static constexpr decltype(auto) apply(Udt&& udt, F&& f) {
+ return hana::unpack(hana::accessors<S>(),
+ hana::partial(struct_detail::almost_demux{},
+ static_cast<F&&>(f),
+ static_cast<Udt&&>(udt)));
+ }
+ };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_UNPACK_HPP