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