List<String> list = ['java', 'c++', 'python', 'javascript', 'dart'];

V test<K, V>(K key, V val) {
  print('$key => $val');
  return val;
}

var name = test('name', '煎蛋');
print(name);

class Mobile<T> {
  final T number;
  Mobile(this.number);
}

var p = Mobile('110');
print(p.number);
var m = Mobile(120);
print(m.number);

class Mobile {
  void powerOn() {
    print('开机...');
  }
}

class Android<T extends Mobile> {
  final T mobile;
  Android(this.mobile);
}

var m = Mobile();
var p = Android<Mobile>(m);
p.mobile.powerOn();