56 lines
1.6 KiB
C++
56 lines
1.6 KiB
C++
/*!
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@file
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Defines `boost::hana::detail::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_DETAIL_INDEX_IF_HPP
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#define BOOST_HANA_DETAIL_INDEX_IF_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/integral_constant.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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namespace boost { namespace hana { namespace detail {
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template <std::size_t i, std::size_t N, bool Done>
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struct index_if_helper;
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template <std::size_t i, std::size_t N>
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struct index_if_helper<i, N, false> {
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template <typename Pred, typename X1, typename ...Xs>
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using f = typename index_if_helper<i + 1, N,
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static_cast<bool>(detail::decay<decltype(
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std::declval<Pred>()(std::declval<X1>()))>::type::value)
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>::template f<Pred, Xs...>;
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};
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template <std::size_t N>
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struct index_if_helper<N, N, false> {
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template <typename ...>
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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 index_if_helper<i, N, true> {
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template <typename ...>
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using f = hana::optional<hana::size_t<i - 1>>;
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};
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template <typename Pred, typename ...Xs>
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struct index_if {
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using type = typename index_if_helper<0, sizeof...(Xs), false>
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::template f<Pred, Xs...>;
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};
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} }} // end namespace boost::hana
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#endif // !BOOST_HANA_DETAIL_INDEX_IF_HPP
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