5ddb118c78
In some cases the actual value of an IMR object is not know at the serialisation time. If the type is fixed-size we can use a placeholder to defer writing it to a more conveninent moment.
64 lines
1.8 KiB
C++
64 lines
1.8 KiB
C++
/*
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* Copyright (C) 2018 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include "utils/fragment_range.hh"
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namespace imr {
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/// No-op deserialisation context
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///
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/// This is a dummy deserialisation context to be used when there is no need
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/// for one, but the interface expects a context object.
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static const struct no_context_t {
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template<typename Tag, typename... Args>
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const no_context_t& context_for(Args&&...) const noexcept { return *this; }
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} no_context;
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struct no_op_continuation {
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template<typename T>
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static T run(T value) noexcept {
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return value;
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}
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};
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template<typename T>
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class placeholder {
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uint8_t* _pointer = nullptr;
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public:
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placeholder() = default;
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explicit placeholder(uint8_t* ptr) noexcept : _pointer(ptr) { }
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void set_pointer(uint8_t* ptr) noexcept { _pointer = ptr; }
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template<typename... Args>
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void serialize(Args&&... args) noexcept {
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if (!_pointer) {
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// We lose the information whether we are in the sizing or
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// serializing phase, hence the need for this run-time check.
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return;
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}
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T::serialize(_pointer, std::forward<Args>(args)...);
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}
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};
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}
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