状態変数の読み込みと書き込みを局所化

state2.dart

class State {
  bool aisatu = false;
  int onigiriPrice = 100;
}

var state = new State();

void onMessage(String message) {
  state = updateState(state, message);
}

State updateState(State _state, String message) {
  switch (message) {
    case "こんにちは":
      return onAisatu(_state);
    case "おにぎり3個ください":
      return onOnigiriRequest(_state);
  }
}

State onAisatu(State _state) {
  print("こんにちは");
  return new State()
    ..onigiriPrice = _state.onigiriPrice
    ..aisatu = true;
}

State onOnigiriRequest(State _state) {
  if (_state.aisatu) {
    var sum = _state.onigiriPrice * 3;
    print("$sum 円です");
    return new State()
      ..onigiriPrice = _state.onigiriPrice
      ..aisatu = false;
  }
  return _state;
}