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/**
* Copyright (C) 2017 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#pragma once
#include "mongo/db/matcher/expression_parser.h"
namespace mongo {
/**
* Classes that must be copyable but want to own a MatchExpression (which deletes its copy
* constructor) can instead store a CopyableMatchExpression.
*
* CopyableMatchExpression stores the BSON expression used to created its MatchExpression, so that
* when we want to copy it, we can create a new MatchExpression that is identical to the old one. We
* only actually perform this operation, however, when the client wants to mutate the
* MatchExpression (by calling setCollator()). The rest of the time, copies of a
* CopyableMatchExpression all point to the same immutable MatchExpression. This pattern is similar
* to copy-on-write semantics.
*/
class CopyableMatchExpression {
public:
/**
* Parse 'matchAST' to create a new MatchExpression, throwing a UserException if we encounter an
* error.
*/
CopyableMatchExpression(BSONObj matchAST,
std::unique_ptr<const ExtensionsCallback> extensionsCallback,
const CollatorInterface* collator)
: _matchAST(matchAST), _extensionsCallback(std::move(extensionsCallback)) {
StatusWithMatchExpression parseResult =
MatchExpressionParser::parse(_matchAST, *_extensionsCallback, collator);
uassertStatusOK(parseResult.getStatus());
_matchExpr = std::move(parseResult.getValue());
}
/**
* Semantically, this behaves as if the client called setCollator() on the underlying
* MatchExpression (which is impossible, because it's const).
*
* Behind the scenes, it actually makes a new MatchExpression with the new collator. That way,
* if there other CopyableMatchExpression objects referencing this MatchExpression, they don't
* see the change in collator.
*/
void setCollator(const CollatorInterface* collator) {
StatusWithMatchExpression parseResult =
MatchExpressionParser::parse(_matchAST, *_extensionsCallback, collator);
invariantOK(parseResult.getStatus());
_matchExpr = std::move(parseResult.getValue());
}
/**
* Overload * so that CopyableMatchExpression can be dereferenced as if it were a pointer to the
* underlying MatchExpression.
*/
const MatchExpression& operator*() {
return *_matchExpr;
}
/**
* Overload -> so that CopyableMatchExpression can be dereferenced as if it were a pointer to
* the underlying MatchExpression.
*/
const MatchExpression* operator->() {
return &(*_matchExpr);
}
private:
BSONObj _matchAST;
std::shared_ptr<const ExtensionsCallback> _extensionsCallback;
std::shared_ptr<const MatchExpression> _matchExpr;
};
} // namespace mongo
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