98 lines
3.0 KiB
C++
98 lines
3.0 KiB
C++
/*!
|
|
@file
|
|
Defines `boost::hana::at_key`.
|
|
|
|
@copyright Louis Dionne 2013-2017
|
|
@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_AT_KEY_HPP
|
|
#define BOOST_HANA_AT_KEY_HPP
|
|
|
|
#include <boost/hana/fwd/at_key.hpp>
|
|
|
|
#include <boost/hana/accessors.hpp>
|
|
#include <boost/hana/at.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/detail/decay.hpp>
|
|
#include <boost/hana/equal.hpp>
|
|
#include <boost/hana/find.hpp>
|
|
#include <boost/hana/find_if.hpp>
|
|
#include <boost/hana/first.hpp>
|
|
#include <boost/hana/functional/on.hpp>
|
|
#include <boost/hana/index_if.hpp>
|
|
#include <boost/hana/length.hpp>
|
|
#include <boost/hana/optional.hpp>
|
|
#include <boost/hana/second.hpp>
|
|
|
|
#include <cstddef>
|
|
#include <utility>
|
|
|
|
|
|
namespace boost { namespace hana {
|
|
//! @cond
|
|
template <typename Xs, typename Key>
|
|
constexpr decltype(auto) at_key_t::operator()(Xs&& xs, Key const& key) const {
|
|
using S = typename hana::tag_of<Xs>::type;
|
|
using AtKey = BOOST_HANA_DISPATCH_IF(at_key_impl<S>,
|
|
hana::Searchable<S>::value
|
|
);
|
|
|
|
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
|
|
static_assert(hana::Searchable<S>::value,
|
|
"hana::at_key(xs, key) requires 'xs' to be Searchable");
|
|
#endif
|
|
|
|
return AtKey::apply(static_cast<Xs&&>(xs), key);
|
|
}
|
|
//! @endcond
|
|
|
|
template <typename S, bool condition>
|
|
struct at_key_impl<S, when<condition>> : default_ {
|
|
template <typename Xs, typename Key>
|
|
static constexpr auto apply(Xs&& xs, Key const& key) {
|
|
return hana::find(static_cast<Xs&&>(xs), key).value();
|
|
}
|
|
};
|
|
|
|
namespace at_key_detail {
|
|
template <typename T>
|
|
struct equal_to {
|
|
T const& t;
|
|
template <typename U>
|
|
constexpr auto operator()(U const& u) const {
|
|
return hana::equal(t, u);
|
|
}
|
|
};
|
|
}
|
|
|
|
template <typename S>
|
|
struct at_key_impl<S, when<hana::Sequence<S>::value>> {
|
|
template <typename Xs, typename Key>
|
|
static constexpr decltype(auto) apply(Xs&& xs, Key const& key) {
|
|
using Result = decltype(hana::index_if(
|
|
static_cast<Xs&&>(xs), at_key_detail::equal_to<Key>{key}));
|
|
|
|
return hana::at(static_cast<Xs&&>(xs), Result{}.value());
|
|
}
|
|
};
|
|
|
|
template <typename S>
|
|
struct at_key_impl<S, when<hana::Struct<S>::value>> {
|
|
template <typename X, typename Key>
|
|
static constexpr decltype(auto) apply(X&& x, Key const& key) {
|
|
auto accessor = hana::second(*hana::find_if(hana::accessors<S>(),
|
|
hana::equal.to(key) ^hana::on^ hana::first
|
|
));
|
|
return accessor(static_cast<X&&>(x));
|
|
}
|
|
};
|
|
}} // end namespace boost::hana
|
|
|
|
#endif // !BOOST_HANA_AT_KEY_HPP
|