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Diffstat (limited to 'boost/hana/fold_left.hpp')
-rw-r--r-- | boost/hana/fold_left.hpp | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/boost/hana/fold_left.hpp b/boost/hana/fold_left.hpp new file mode 100644 index 0000000000..23fee4035f --- /dev/null +++ b/boost/hana/fold_left.hpp @@ -0,0 +1,97 @@ +/*! +@file +Defines `boost::hana::fold_left`. + +@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_FOLD_LEFT_HPP +#define BOOST_HANA_FOLD_LEFT_HPP + +#include <boost/hana/fwd/fold_left.hpp> + +#include <boost/hana/concept/foldable.hpp> +#include <boost/hana/config.hpp> +#include <boost/hana/core/dispatch.hpp> +#include <boost/hana/detail/variadic/foldl1.hpp> +#include <boost/hana/functional/partial.hpp> +#include <boost/hana/unpack.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @cond + template <typename Xs, typename State, typename F> + constexpr decltype(auto) fold_left_t::operator()(Xs&& xs, State&& state, F&& f) const { + using S = typename hana::tag_of<Xs>::type; + using FoldLeft = BOOST_HANA_DISPATCH_IF(fold_left_impl<S>, + hana::Foldable<S>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Foldable<S>::value, + "hana::fold_left(xs, state, f) requires 'xs' to be Foldable"); + #endif + + return FoldLeft::apply(static_cast<Xs&&>(xs), + static_cast<State&&>(state), + static_cast<F&&>(f)); + } + + template <typename Xs, typename F> + constexpr decltype(auto) fold_left_t::operator()(Xs&& xs, F&& f) const { + using S = typename hana::tag_of<Xs>::type; + using FoldLeft = BOOST_HANA_DISPATCH_IF(fold_left_impl<S>, + hana::Foldable<S>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Foldable<S>::value, + "hana::fold_left(xs, f) requires 'xs' to be Foldable"); + #endif + + return FoldLeft::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f)); + } + //! @endcond + + namespace detail { + template <typename F, typename State> + struct variadic_foldl1 { + F& f; + State& state; + template <typename ...T> + constexpr decltype(auto) operator()(T&& ...t) const { + return detail::variadic::foldl1( + static_cast<F&&>(f), + static_cast<State&&>(state), + static_cast<T&&>(t)... + ); + } + }; + } + + template <typename T, bool condition> + struct fold_left_impl<T, when<condition>> : default_ { + // with state + template <typename Xs, typename S, typename F> + static constexpr decltype(auto) apply(Xs&& xs, S&& s, F&& f) { + return hana::unpack(static_cast<Xs&&>(xs), + detail::variadic_foldl1<F, S>{f, s} + ); + } + + // without state + template <typename Xs, typename F> + static constexpr decltype(auto) apply(Xs&& xs, F&& f) { + return hana::unpack(static_cast<Xs&&>(xs), + hana::partial( + detail::variadic::foldl1, + static_cast<F&&>(f) + ) + ); + } + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FOLD_LEFT_HPP |