anchor.diff:  
   main() {
     var series = new GameFactory('Professor Falken', 'Joshua');
  -  print(series);
   
  -  var game;
  -  game = series.createBoardGame('Checkers');
  -  print(game);
  -
  -  game = series.createBoardGame('Thermo Nuclear War');
  -  print(game);
  -
  -  game = series.createBoardGame();
  -  print(game);
  +  series
  +    ..start()
  +    ..createBoardGame('Checkers').play()
  +    ..createBoardGame('Thermo Nuclear War').play()
  +    ..createBoardGame().play();
   }
  
positive.code: class GameFactory {
    String playerOne, playerTwo;
    GameFactory(this.playerOne, this.playerTwo);
    String toString() => "*** $playerOne vs. $playerTwo ***";
  
    // The factory method
  
negative.code: class BoardGame {
    List playerOnePieces = [];
    List playerTwoPieces = [];
    void play() { print(this); }
    String get winner => new Random().nextBool() ? "Player One" : "Player Two";
    String toString() =>
      "  ${this.runtimeType}\n"
      "    Player One starts with: ${playerOnePieces.join(', ')}\n"
      "    Player Two starts with: ${playerTwoPieces.join(', ')}\n"
      "    --\n"
      "    Winner: $winner\n";
  }
  
  