86 lines
2.8 KiB
C++
86 lines
2.8 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2017-2018 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_VARIADIC_HPP
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#define CRUFT_UTIL_VARIADIC_HPP
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#include <cstddef>
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#include <type_traits>
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#include <utility>
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#include <tuple>
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namespace util::variadic {
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///////////////////////////////////////////////////////////////////////////
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/// do nothing with a set of parameters.
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///
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/// useful for temporarily silencing unused argument warnings in parameter
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/// packs, or for avoiding assignment of [[gnu::warn_unused_result]] to a
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/// temporary value we'd just cast to void anyway (GCC#66425).
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///
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/// it is guaranteed that this function will never be defined out in
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/// debug/release/whatever builds. so it is safe to use to guarantee
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/// parameter evaluation.
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template <typename ...Args>
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void
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ignore (const Args&...) noexcept ((std::is_nothrow_destructible_v<Args> && ...))
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{ ; }
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///////////////////////////////////////////////////////////////////////////
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/// Returns the argument at index `IndexV', as if we called:
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/// std::get<N> (std::make_tuple (...))
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template <std::size_t IndexV, typename HeadT, typename ...TailT>
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auto
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get (HeadT &&head, TailT &&...tail) noexcept ((std::is_nothrow_move_constructible_v<TailT> && ...))
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{
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static_assert (IndexV < sizeof... (TailT) + 1, "Index is out of bounds");
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if constexpr (IndexV == 0)
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return std::forward<HeadT> (head);
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else
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return get<IndexV-1> (std::forward<TailT> (tail)...);
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}
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///////////////////////////////////////////////////////////////////////////
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/// returns a tuple of all arguments that satisfy the trait QueryT
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template <template <typename> class QueryT>
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auto filter () { return std::tuple {}; }
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/// returns a tuple of all arguments that satisfy the trait QueryT
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template <
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template <typename> class QueryT,
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typename HeadT,
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typename ...ArgsT
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>
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auto
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filter (HeadT &&head, ArgsT &&...args)
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{
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if constexpr (QueryT<HeadT>::value)
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return std::tuple_cat (
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std::tuple (std::forward<HeadT> (head)),
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filter<QueryT> (std::forward<ArgsT> (args)...)
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);
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else
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return filter<QueryT> (std::forward<ArgsT> (args)...);
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}
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};
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#endif
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