93 lines
3.4 KiB
C++
93 lines
3.4 KiB
C++
/*
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* This file is open source software, licensed to you under the terms
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* of the Apache License, Version 2.0 (the "License"). See the NOTICE file
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* distributed with this work for additional information regarding copyright
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* ownership. You may not use this file except in compliance with the License.
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*
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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,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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*/
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/*
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* Copyright (C) 2015 Cloudius Systems, Ltd.
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*/
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#pragma once
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#include "apply.hh"
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#include <utility>
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#include <memory>
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#include <tuple>
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/// \addtogroup future-util
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/// @{
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/// do_with() holds an object alive for the duration until a future
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/// completes, and allow the code involved in making the future
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/// complete to have easy access to this object.
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///
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/// do_with() takes two arguments: The first is an temporary object (rvalue),
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/// the second is a function returning a future (a so-called "promise").
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/// The function is given (a moved copy of) this temporary object, by
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/// reference, and it is ensured that the object will not be destructed until
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/// the completion of the future returned by the function.
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///
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/// do_with() returns a future which resolves to whatever value the given future
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/// (returned by the given function) resolves to. This returned value must not
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/// contain references to the temporary object, as at that point the temporary
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/// is destructed.
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///
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/// \param rvalue a temporary value to protect while \c f is running
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/// \param f a callable, accepting an lvalue reference of the same type
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/// as \c rvalue, that will be accessible while \c f runs
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/// \return whatever \c f returns
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template<typename T, typename F>
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inline
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auto do_with(T&& rvalue, F&& f) {
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auto obj = std::make_unique<T>(std::forward<T>(rvalue));
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auto fut = f(*obj);
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return fut.finally([obj = std::move(obj)] () {});
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}
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/// \cond internal
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template <typename Tuple, size_t... Idx>
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inline
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auto
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cherry_pick_tuple(std::index_sequence<Idx...>, Tuple&& tuple) {
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return std::make_tuple(std::get<Idx>(std::forward<Tuple>(tuple))...);
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}
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/// \endcond
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/// Multiple argument variant of \ref do_with(T&& rvalue, F&& f).
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///
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/// This is the same as \ref do_with(T&& tvalue, F&& f), but accepts
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/// two or more rvalue parameters, which are held in memory while
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/// \c f executes. \c f will be called with all arguments as
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/// reference parameters.
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template <typename T1, typename T2, typename T3_or_F, typename... More>
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inline
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auto
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do_with(T1&& rv1, T2&& rv2, T3_or_F&& rv3, More&&... more) {
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auto all = std::forward_as_tuple(
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std::forward<T1>(rv1),
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std::forward<T2>(rv2),
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std::forward<T3_or_F>(rv3),
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std::forward<More>(more)...);
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constexpr size_t nr = std::tuple_size<decltype(all)>::value - 1;
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using idx = std::make_index_sequence<nr>;
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auto&& just_values = cherry_pick_tuple(idx(), std::move(all));
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auto&& just_func = std::move(std::get<nr>(std::move(all)));
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auto obj = std::make_unique<std::remove_reference_t<decltype(just_values)>>(std::move(just_values));
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auto fut = apply(just_func, *obj);
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return fut.finally([obj = std::move(obj)] () {});
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}
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/// @}
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