/*! @file Defines `boost::hana::count_if`. @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_COUNT_IF_HPP #define BOOST_HANA_COUNT_IF_HPP #include <boost/hana/fwd/count_if.hpp> #include <boost/hana/concept/foldable.hpp> #include <boost/hana/config.hpp> #include <boost/hana/core/dispatch.hpp> #include <boost/hana/detail/algorithm.hpp> #include <boost/hana/detail/fast_and.hpp> #include <boost/hana/integral_constant.hpp> #include <boost/hana/unpack.hpp> #include <cstddef> #include <type_traits> #include <utility> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename Xs, typename Pred> constexpr auto count_if_t::operator()(Xs&& xs, Pred&& pred) const { using S = typename hana::tag_of<Xs>::type; using CountIf = BOOST_HANA_DISPATCH_IF(count_if_impl<S>, hana::Foldable<S>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Foldable<S>::value, "hana::count_if(xs, pred) requires 'xs' to be Foldable"); #endif return CountIf::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred)); } //! @endcond namespace detail { template <typename Pred> struct count_pred { Pred pred; template <typename ...Xs, typename = typename std::enable_if< detail::fast_and< Constant<decltype((*pred)(std::declval<Xs&&>()))>::value... >::value >::type> constexpr auto operator()(Xs&& ...xs) const { constexpr bool results[] = {false, // <-- avoid empty array static_cast<bool>(hana::value<decltype((*pred)(static_cast<Xs&&>(xs)))>())... }; constexpr std::size_t total = detail::count( results, results + sizeof(results), true ); return hana::size_c<total>; } template <typename ...Xs, typename = void, typename = typename std::enable_if< !detail::fast_and< Constant<decltype((*pred)(std::declval<Xs&&>()))>::value... >::value >::type> constexpr auto operator()(Xs&& ...xs) const { std::size_t total = 0; using Swallow = std::size_t[]; (void)Swallow{0, ((*pred)(static_cast<Xs&&>(xs)) ? ++total : 0)...}; return total; } }; } template <typename T, bool condition> struct count_if_impl<T, when<condition>> : default_ { template <typename Xs, typename Pred> static constexpr decltype(auto) apply(Xs&& xs, Pred&& pred) { // We use a pointer instead of a reference to avoid a Clang ICE. return hana::unpack(static_cast<Xs&&>(xs), detail::count_pred<decltype(&pred)>{&pred} ); } }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_COUNT_IF_HPP