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Diffstat (limited to 'boost/hana/unpack.hpp')
-rw-r--r-- | boost/hana/unpack.hpp | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/boost/hana/unpack.hpp b/boost/hana/unpack.hpp new file mode 100644 index 0000000000..03a4faed93 --- /dev/null +++ b/boost/hana/unpack.hpp @@ -0,0 +1,141 @@ +/*! +@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 |