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/**
* Copyright (C) 2012 10gen 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/>.
*/
#pragma once
#include <boost/scoped_array.hpp>
#include <string>
#include <vector>
#include "mongo/base/disallow_copying.h"
#include "mongo/base/string_data.h"
namespace mongo {
/**
* A FieldPath represents a path in a document, starting from the root. The path
* is made of "field parts" separated by dots. The class provides an efficient means to
* "split" the dotted fields in its parts, but no validation is done.
*
* Any field part may be replaced, after the "original" field reference was parsed. Any
* part can be accessed through a StringData object.
*
* The class is not thread safe.
*/
class FieldRef {
MONGO_DISALLOW_COPYING(FieldRef);
public:
FieldRef() : _size(0) {}
/**
* Field parts accessed through getPart() calls no longer would be valid, after the
* destructor ran.
*/
~FieldRef() {}
/**
* Builds a field path out of each field part in 'dottedField'.
*/
void parse(const StringData& dottedField);
/**
* Sets the 'i-th' field part to point to 'part'. Assumes i < size(). Behavior is
* undefined otherwise.
*/
void setPart(size_t i, const StringData& part);
/**
* Returns the 'i-th' field part. Assumes i < size(). Behavior is undefined otherwise.
*/
StringData getPart(size_t i) const;
/**
* Returns a copy of the full dotted field in its current state (i.e., some parts may
* have been replaced since the parse() call).
*/
std::string dottedField() const;
/**
* Resets the internal state. See note in parse() call.
*/
void clear();
//
// accessors
//
/**
* Returns the number of parts in this FieldRef.
*/
size_t numParts() const { return _size; }
/**
* Returns the number of fields parts that were replaced so far. Replacing the same
* fields several times only counts for 1.
*/
size_t numReplaced() const;
private:
// Dotted fields are most often not longer than three parts. We use a mixed structure
// here that will not require any extra memory allocation when that is the case. And
// handle larger dotted fields if it is. The idea is not to penalize the common case
// with allocations.
static const size_t kReserveAhead = 4;
size_t _size; // # of field parts stored
StringData _fixed[kReserveAhead]; // first kResevedAhead field components
std::vector<StringData> _variable; // remaining field components
// Areas that _fixed and _variable point to.
boost::scoped_array<char> _fieldBase; // concatenation of null-terminated parts
std::vector<std::string> _replacements; // added with the setPart call
/** Converts the field part index to the variable part equivalent */
size_t getIndex(size_t i) const { return i-kReserveAhead; }
/**
* Returns the new number of parts after appending 'part' to this field path. It
* assumes that 'part' is pointing to an internally allocated area.
*/
size_t appendPart(const StringData& part);
};
} // namespace mongo
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