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 Hu Chunming
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/*!
@file
Defines `boost::hana::find_if`.
Copyright Louis Dionne 2013-2022
Copyright Jason Rice 2017
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_FIND_IF_HPP
#define BOOST_HANA_FIND_IF_HPP
#include <boost/hana/fwd/find_if.hpp>
#include <boost/hana/accessors.hpp>
#include <boost/hana/at.hpp>
#include <boost/hana/bool.hpp>
#include <boost/hana/concept/iterable.hpp>
#include <boost/hana/concept/searchable.hpp>
#include <boost/hana/concept/struct.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/first.hpp>
#include <boost/hana/functional/compose.hpp>
#include <boost/hana/index_if.hpp>
#include <boost/hana/second.hpp>
#include <boost/hana/transform.hpp>
#include <cstddef>
#include <utility>
namespace boost { namespace hana {
//! @cond
template <typename Xs, typename Pred>
constexpr auto find_if_t::operator()(Xs&& xs, Pred&& pred) const {
using S = typename hana::tag_of<Xs>::type;
using FindIf = BOOST_HANA_DISPATCH_IF(find_if_impl<S>,
hana::Searchable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Searchable<S>::value,
"hana::find_if(xs, pred) requires 'xs' to be a Searchable");
#endif
return FindIf::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
}
//! @endcond
template <typename S, bool condition>
struct find_if_impl<S, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
namespace detail {
template <typename Xs>
struct partial_at {
Xs const& xs;
template <typename I>
constexpr decltype(auto) operator()(I i) const {
return hana::at(xs, i);
}
};
}
template <typename Tag>
struct find_if_impl<Tag, when<Iterable<Tag>::value>> {
template <typename Xs, typename Pred>
static constexpr auto apply(Xs&& xs, Pred&& pred) {
using Result = decltype(hana::index_if(
static_cast<Xs&&>(xs), static_cast<Pred&&>(pred)));
return hana::transform(Result{},
detail::partial_at<std::decay_t<Xs>>{static_cast<Xs&&>(xs)});
}
};
template <typename T, std::size_t N>
struct find_if_impl<T[N]> {
template <typename Xs>
static constexpr auto find_if_helper(Xs&&, hana::false_)
{ return hana::nothing; }
template <typename Xs>
static constexpr auto find_if_helper(Xs&& xs, hana::true_)
{ return hana::just(static_cast<Xs&&>(xs)[0]); }
template <typename Xs, typename Pred>
static constexpr auto apply(Xs&& xs, Pred&& pred) {
return find_if_helper(static_cast<Xs&&>(xs),
hana::bool_c<decltype(
static_cast<Pred&&>(pred)(static_cast<Xs&&>(xs)[0])
)::value>
);
}
};
namespace struct_detail {
template <typename X>
struct get_member {
X x;
template <typename Member>
constexpr decltype(auto) operator()(Member&& member) && {
return hana::second(static_cast<Member&&>(member))(
static_cast<X&&>(x)
);
}
};
}
template <typename S>
struct find_if_impl<S, when<hana::Struct<S>::value>> {
template <typename X, typename Pred>
static constexpr decltype(auto) apply(X&& x, Pred&& pred) {
return hana::transform(
hana::find_if(hana::accessors<S>(),
hana::compose(static_cast<Pred&&>(pred), hana::first)
),
struct_detail::get_member<X>{static_cast<X&&>(x)}
);
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_FIND_IF_HPP
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