72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
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/*!
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@file
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Defines `boost::hana::detail::index_if`.
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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_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/core/when.hpp>
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#include <cstddef>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN namespace detail {
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template <typename ...T>
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struct pack {
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static constexpr std::size_t length = sizeof...(T);
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};
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template <typename T>
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struct make_pack;
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template <template <typename...> class Template, typename ...T>
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struct make_pack<Template<T...>> {
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using type = pack<T...>;
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};
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template <typename T> struct make_pack<T const> : make_pack<T> { };
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template <typename T> struct make_pack<T&> : make_pack<T> { };
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template <typename T> struct make_pack<T&&> : make_pack<T> { };
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//! @ingroup group-details
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//! Returns the index of the first element of the `pack<>` that satisfies
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//! the predicate, or the size of the pack if there is no such element.
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//!
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//! @note
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//! The predicate must return an `IntegralConstant` that can be explicitly
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//! converted to `bool`.
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template <typename Pred, typename Ts, typename = when<true>>
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struct index_if;
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//! @cond
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template <typename Pred, typename T, typename ...Ts>
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struct index_if<Pred, pack<T, Ts...>, when<static_cast<bool>(decltype(
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std::declval<Pred>()(std::declval<T>())
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)::value)>> {
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static constexpr std::size_t value = 0;
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};
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template <typename Pred, typename T, typename ...Ts>
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struct index_if<Pred, pack<T, Ts...>, when<!static_cast<bool>(decltype(
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std::declval<Pred>()(std::declval<T>())
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)::value)>> {
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static constexpr std::size_t value = 1 + index_if<Pred, pack<Ts...>>::value;
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};
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template <typename Pred>
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struct index_if<Pred, pack<>> {
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static constexpr std::size_t value = 0;
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};
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//! @endcond
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} BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_DETAIL_INDEX_IF_HPP
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