text: // matchable.h
  
  /**
   *    Copyright (C) 2013 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/>.
   *
   *    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/bson/bsonobj.h"
  #include "mongo/db/field_ref.h"
  #include "mongo/db/matcher/path.h"
  
  namespace mongo {
  
  class MatchableDocument {
  public:
      // Inlining to allow subclasses to see that this is a no-op and avoid a function call.
      // Speeds up query execution measurably.
      virtual ~MatchableDocument() {}
  
      virtual BSONObj toBSON() const = 0;
  
      /**
       * The neewly returned ElementIterator is allowed to keep a pointer to path.
       * So the caller of this function should make sure path is in scope until
       * the ElementIterator is deallocated
      */
      virtual ElementIterator* allocateIterator(const ElementPath* path) const = 0;
  
      virtual void releaseIterator(ElementIterator* iterator) const = 0;
  
      class IteratorHolder {
      public:
          IteratorHolder(const MatchableDocument* doc, const ElementPath* path) {
              _doc = doc;
              _iterator = _doc->allocateIterator(path);
          }
  
          ~IteratorHolder() {
              _doc->releaseIterator(_iterator);
          }
  
          ElementIterator* operator->() const {
              return _iterator;
          }
  
      private:
          const MatchableDocument* _doc;
          ElementIterator* _iterator;
      };
  };
  
  class BSONMatchableDocument : public MatchableDocument {
  public:
      BSONMatchableDocument(const BSONObj& obj);
      virtual ~BSONMatchableDocument();
  
      virtual BSONObj toBSON() const {
          return _obj;
      }
  
      virtual ElementIterator* allocateIterator(const ElementPath* path) const {
          if (_iteratorUsed)
              return new BSONElementIterator(path, _obj);
          _iteratorUsed = true;
          _iterator.reset(path, _obj);
          return &_iterator;
      }
  
      virtual void releaseIterator(ElementIterator* iterator) const {
          if (iterator == &_iterator) {
              _iteratorUsed = false;
          } else {
              delete iterator;
          }
      }
  
  private:
      BSONObj _obj;
      mutable BSONElementIterator _iterator;
      mutable bool _iteratorUsed;
  };
  }
  