38a54df863
People keep tripping over the old copyrights and copy-pasting them to new files. Search and replace "Cloudius Systems" with "ScyllaDB". Message-Id: <1460013664-25966-1-git-send-email-penberg@scylladb.com>
70 lines
2.1 KiB
C++
70 lines
2.1 KiB
C++
/*
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* Copyright (C) 2016 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/allocation_strategy.hh"
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#include <seastar/util/defer.hh>
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//
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// ~~ Definitions ~~
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//
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// Mergeable type is a type which has an associated "apply" binary operation (T x T -> T)
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// which forms a commutative semigroup with instances of that type.
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//
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// ReversiblyMergeable type is a Mergeable type which has two binary operations associated,
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// "apply_reversibly" and "revert", both working on objects of that type (T x T -> T x T)
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// with the following properties:
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//
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// apply_reversibly(x, y) = (x', y')
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// revert(x', y') = (x'', y'')
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//
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// x' = apply(x, y)
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// x'' = x
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// apply(x'', y'') = apply(x, y)
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//
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// Note that it is not guaranteed that y'' = y and the state of y' is unspecified.
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//
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// ~~ API ~~
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//
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// "apply_reversibly" and "revert" are usually implemented as instance methods or functions
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// mutating both arguments to store the result of the operation in them.
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//
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// "revert" is not allowed to throw. If "apply_reversibly" throws the objects on which it operates
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// are left in valid states, with guarantees the same as if a successful apply_reversibly() was
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// followed by revert().
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//
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template<typename T>
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struct default_reversible_applier {
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void operator()(T& dst, T& src) const {
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dst.apply_reversibly(src);
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}
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};
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template<typename T>
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struct default_reverter {
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void operator()(T& dst, T& src) const noexcept {
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dst.revert(src);
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}
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};
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