anchor.diff:  
       cursor.skip = skip;
       cursor.limit = limit;
  -        
  +    
  +    var sc = new StreamController();
  +    
       return cursor.stream.asyncMap((m) {
         if(!_known.containsKey(m["_id"])) {
           var obj = _dty.mirror.newInstance(#revive, [m]).reflectee;
  
positive.code:       } else {
          // Explicitly *DONT* override members here to avoid clobbering unsaved
          // changes
          print("Map ${m} to known ${m['_id']}");
          return _known[m["_id"]];
        }
      });
  
negative.code: 
  class Database {
    String _connStr;
    mdb.Db _db;
    Future _openFuture;
    
    Database(String connectionString) 
        : _connStr = connectionString
        , _db = new mdb.Db(connectionString) {
    }
    
    Future<Connection> connect() {
      if(_openFuture == null) {
        _openFuture = _db.open();
      }
      
      return _openFuture.then((_) => new _Connection(_db));
    }
  }
  
  