/*!
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@file
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Defines `boost::hana::index_if`.
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@copyright Louis Dionne 2013-2017
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@copyright Jason Rice 2017
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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_INDEX_IF_HPP
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#define BOOST_HANA_INDEX_IF_HPP
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#include <boost/hana/concept/foldable.hpp>
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#include <boost/hana/concept/iterable.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <boost/hana/detail/index_if.hpp>
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#include <boost/hana/fwd/at.hpp>
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#include <boost/hana/fwd/basic_tuple.hpp>
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#include <boost/hana/fwd/index_if.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/length.hpp>
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#include <boost/hana/optional.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 Pred>
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constexpr auto index_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 IndexIf = BOOST_HANA_DISPATCH_IF(index_if_impl<S>,
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hana::Iterable<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Iterable<S>::value,
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"hana::index_if(xs, pred) requires 'xs' to be a Iterable");
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#endif
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return IndexIf::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
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}
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//! @endcond
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namespace detail {
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template <std::size_t i, std::size_t N, bool Done>
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struct iterate_while;
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template <std::size_t i, std::size_t N>
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struct iterate_while<i, N, false> {
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template <typename Xs, typename Pred>
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using f = typename iterate_while<i + 1, N,
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static_cast<bool>(detail::decay<decltype(
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std::declval<Pred>()(
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hana::at(std::declval<Xs>(), hana::size_c<i>)))>::type::value)
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>::template f<Xs, Pred>;
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};
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template <std::size_t N>
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struct iterate_while<N, N, false> {
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template <typename Xs, typename Pred>
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using f = hana::optional<>;
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};
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template <std::size_t i, std::size_t N>
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struct iterate_while<i, N, true> {
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template <typename Xs, typename Pred>
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using f = hana::optional<hana::size_t<i - 1>>;
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};
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}
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template <typename Tag>
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struct index_if_impl<Tag, when<Foldable<Tag>::value>> {
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template <typename Xs, typename Pred>
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static constexpr auto apply(Xs const& xs, Pred const&)
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-> typename detail::iterate_while<0,
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decltype(hana::length(xs))::value, false>
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::template f<Xs, Pred>
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{ return {}; }
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};
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template <typename It>
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struct index_if_impl<It, when<!Foldable<It>::value>> {
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template <typename Xs, typename Pred>
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static constexpr auto apply(Xs const&, Pred const&)
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-> typename detail::iterate_while<0,
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static_cast<std::size_t>(-1), false>
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::template f<Xs, Pred>
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{ return {}; }
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};
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// basic_tuple is implemented here to solve circular dependency issues.
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template <>
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struct index_if_impl<basic_tuple_tag> {
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template <typename ...Xs, typename Pred>
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static constexpr auto apply(basic_tuple<Xs...> const&, Pred const&)
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-> typename detail::index_if<Pred, Xs...>::type
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{ return {}; }
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_INDEX_IF_HPP
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