122 lines
4.1 KiB
C++
122 lines
4.1 KiB
C++
/*!
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@file
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Defines `boost::hana::at_key`.
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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_AT_KEY_HPP
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#define BOOST_HANA_AT_KEY_HPP
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#include <boost/hana/fwd/at_key.hpp>
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#include <boost/hana/accessors.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/searchable.hpp>
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#include <boost/hana/concept/struct.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/decay.hpp>
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#include <boost/hana/equal.hpp>
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#include <boost/hana/find.hpp>
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#include <boost/hana/find_if.hpp>
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#include <boost/hana/first.hpp>
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#include <boost/hana/functional/on.hpp>
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#include <boost/hana/length.hpp>
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#include <boost/hana/optional.hpp>
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#include <boost/hana/second.hpp>
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#include <cstddef>
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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 Key>
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constexpr decltype(auto) at_key_t::operator()(Xs&& xs, Key const& key) const {
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using S = typename hana::tag_of<Xs>::type;
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using AtKey = BOOST_HANA_DISPATCH_IF(at_key_impl<S>,
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hana::Searchable<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Searchable<S>::value,
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"hana::at_key(xs, key) requires 'xs' to be Searchable");
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#endif
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return AtKey::apply(static_cast<Xs&&>(xs), key);
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}
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//! @endcond
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template <typename S, bool condition>
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struct at_key_impl<S, when<condition>> : default_ {
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template <typename Xs, typename Key>
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static constexpr auto apply(Xs&& xs, Key const& key) {
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return hana::find(static_cast<Xs&&>(xs), key).value();
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}
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};
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namespace at_key_detail {
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template <typename T>
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struct equal_to {
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T const& t;
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template <typename U>
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constexpr auto operator()(U const& u) const {
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return hana::equal(t, u);
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}
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};
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//! @todo This causes an awful duplication of code with `find_if`.
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template <typename Xs, typename Pred, std::size_t i, std::size_t N, bool Done>
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struct advance_until;
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template <typename Xs, typename Pred, std::size_t i, std::size_t N>
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struct advance_until<Xs, Pred, i, N, false>
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: advance_until<Xs, Pred, i + 1, N, static_cast<bool>(detail::decay<decltype(
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std::declval<Pred>()(hana::at_c<i>(std::declval<Xs>()))
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)>::type::value)>
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{ };
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template <typename Xs, typename Pred, std::size_t N>
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struct advance_until<Xs, Pred, N, N, false> {
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template <typename Ys>
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static constexpr auto apply(Ys&&) = delete;
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};
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template <typename Xs, typename Pred, std::size_t i, std::size_t N>
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struct advance_until<Xs, Pred, i, N, true> {
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template <typename Ys>
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static constexpr decltype(auto) apply(Ys&& ys) {
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return hana::at_c<i - 1>(static_cast<Ys&&>(ys));
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}
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};
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}
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template <typename S>
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struct at_key_impl<S, when<hana::Sequence<S>::value>> {
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template <typename Xs, typename Key>
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static constexpr decltype(auto) apply(Xs&& xs, Key const&) {
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constexpr std::size_t N = decltype(hana::length(xs))::value;
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using Pred = at_key_detail::equal_to<Key>;
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return at_key_detail::advance_until<Xs&&, Pred, 0, N, false>::apply(
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static_cast<Xs&&>(xs)
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);
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}
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};
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template <typename S>
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struct at_key_impl<S, when<hana::Struct<S>::value>> {
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template <typename X, typename Key>
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static constexpr decltype(auto) apply(X&& x, Key const& key) {
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auto accessor = hana::second(*hana::find_if(hana::accessors<S>(),
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hana::equal.to(key) ^hana::on^ hana::first
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));
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return accessor(static_cast<X&&>(x));
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_AT_KEY_HPP
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