final String name = "Po";
  final int age = 18;
  print("I am $name, $age years old");
  // I am Po, 18 years old

  int.parse("1") // 1
  double.parse('1.1') // 1.1
  try {
    int.parse("1xx");
  } catch (e) {
     print(e.toString());
     // FormatException: 1xx
  }

  final String text = "123213,321321";
  text.split(',') // [123213, 321321]

  final List<String> list = ["123213", "321321"];
  list.join(',') // "123213,321321"

  final List<Point> list = [Point(3, 4), Point(1, 2)];
  Map.fromIterable(list, key: (e) => e.x, value: (e) => e.y); // {3: 4, 1: 2}

  final List<Point> list = [Point(3, 4), Point(1, 2)];
  final List<String> listWithIndex = list.asMap().entries.map((entry) {
    final int index = entry.key;
    final Point value = entry.value;
    return "${index}:{${value.x},${value.y}}";
  }).toList(growable: false);
  // ["0:{3,4}", "1:{1,2}"]

  // compute the sum of all length
  final List<String> list = ['a', 'bb', 'ccc'];
  final int result = list.fold(
      0,
      (final int previousValue, final String element) => previousValue + element.length);
  print(result); // 6

  final List<String> keys = ['x', 'y', 'z'];
  final List<int> values = [1, 2, 3];

  Map<String, int>.fromIterables(keys, values);  // {x: 1, y: 2, z: 3}

  final Map<String, int> map = {"x": 3, "y": 4};
  final List<int> list = [];
  map.forEach((k, v) => list.add(v));
  print(list); // [3, 4]