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/*!
@file
Defines `boost::hana::count_if`.
Copyright Louis Dionne 2013-2022
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>
namespace boost { namespace hana {
//! @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}
);
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_COUNT_IF_HPP
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