【Dart】入門04-計算屬性

計算屬性我認爲get是方便調用並且保證內部變量的私密性，set是爲了確保程序的健壯性。我們以一個小計算器爲例。

void main() {
  var _calculator = Calculator(1, 1);
  try {
    _calculator.operation = '++';
  } catch (e) {
    print(e.toString());
  }

  _calculator.operation = '+';
  print(_calculator.result);
}

class Calculator {
  num num1, num2;
  String _operation;
  Calculator(
    this.num1,
    this.num2,
  );
  num get result {
    num _result;
    switch (this._operation) {
      case "+":
        _result = num1 + num2;
        break;
      case "-":
        _result = num1 - num2;
        break;
      case "*":
        _result = num1 * num2;
        break;
      case "/":
        _result = num1 / num2;
        break;
    }
    return _result;
  }

  set operation(String value) {
    if (value.length == 1) {
      if (!'+-*/'.contains(value)) {
        throw Exception('operation Error');
      } else {
        this._operation = value;
      }
    } else {
      throw Exception('operation lengthError');
    }
    //
  }
}

運行結果