anchor.diff:      return completer.future;
     }
     
  -  Future distinct(String field, [selector]){
  -    Completer completer = new Completer();
  -    db.executeDbCommand(DbCommand.createDistinctCommand(db,collectionName,field,_selectorBuilder2Map(selector))).then((reply){
  -      completer.complete(reply);
  -    });
  -    return completer.future;
  -  }
  +  Future distinct(String field, [selector]) =>
  +    db.executeDbCommand(DbCommand.createDistinctCommand(db,collectionName,field,_selectorBuilder2Map(selector)))
     
     Future aggregate(List pipeline){
  -    Completer completer = new Completer();
       var cmd = DbCommand.createAggregateCommand(db,collectionName,pipeline);
  -    db.executeDbCommand(cmd)
  -      .then((reply){
  -      completer.complete(reply);
  -    });
  -    
  -    return completer.future;
  +    return db.executeDbCommand(cmd);
     }
     
     Future insert(Map document, {WriteConcern writeConcern}) => insertAll([document], writeConcern: writeConcern);
  
positive.code:       }
      }
      if (id != null){
        update({"_id": id}, document, writeConcern: writeConcern);
      }
      else{
        if (createId) {
          document["_id"] = new ObjectId();
        }
        insert(document, writeConcern: writeConcern);
      }
    }
   Future insertAll(List<Map> documents, {WriteConcern writeConcern}){
  
negative.code:     }
      return selector;
    }
  }
  