/*! @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