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