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98 lines
3.1 KiB
C++
98 lines
3.1 KiB
C++
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/*!
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@file
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Defines `boost::hana::fold_left`.
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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_FOLD_LEFT_HPP
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#define BOOST_HANA_FOLD_LEFT_HPP
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#include <boost/hana/fwd/fold_left.hpp>
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#include <boost/hana/concept/foldable.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/detail/variadic/foldl1.hpp>
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#include <boost/hana/functional/partial.hpp>
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#include <boost/hana/unpack.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename State, typename F>
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constexpr decltype(auto) fold_left_t::operator()(Xs&& xs, State&& state, F&& f) const {
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using S = typename hana::tag_of<Xs>::type;
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using FoldLeft = BOOST_HANA_DISPATCH_IF(fold_left_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::fold_left(xs, state, f) requires 'xs' to be Foldable");
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#endif
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return FoldLeft::apply(static_cast<Xs&&>(xs),
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static_cast<State&&>(state),
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static_cast<F&&>(f));
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}
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template <typename Xs, typename F>
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constexpr decltype(auto) fold_left_t::operator()(Xs&& xs, F&& f) const {
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using S = typename hana::tag_of<Xs>::type;
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using FoldLeft = BOOST_HANA_DISPATCH_IF(fold_left_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::fold_left(xs, f) requires 'xs' to be Foldable");
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#endif
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return FoldLeft::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f));
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}
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//! @endcond
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namespace detail {
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template <typename F, typename State>
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struct variadic_foldl1 {
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F& f;
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State& state;
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template <typename ...T>
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constexpr decltype(auto) operator()(T&& ...t) const {
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return detail::variadic::foldl1(
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static_cast<F&&>(f),
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static_cast<State&&>(state),
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static_cast<T&&>(t)...
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);
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}
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};
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}
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template <typename T, bool condition>
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struct fold_left_impl<T, when<condition>> : default_ {
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// with state
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template <typename Xs, typename S, typename F>
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static constexpr decltype(auto) apply(Xs&& xs, S&& s, F&& f) {
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return hana::unpack(static_cast<Xs&&>(xs),
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detail::variadic_foldl1<F, S>{f, s}
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);
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}
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// without state
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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::unpack(static_cast<Xs&&>(xs),
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hana::partial(
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detail::variadic::foldl1,
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static_cast<F&&>(f)
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)
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);
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FOLD_LEFT_HPP
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