2021-03-04 flutter null类型赋值给其他类型

void main() {
  var b = null;//可以
  try {
    double a = b;//不会抛异常
    print(a);//null
    if (a is double) {//不执行
      print('a is double');
    }
    if (a == null) {//a is null
      print('a is null');
    }
  } catch (e) {
    print(e);
  }
  String string = '👩👩👦👨👨👧';
  print(string.length);
  String trimString = string.trim();
  print(trimString.length);
  print(trimString);

  String result = string.substring(0, 10);
  print(result);
  for (int i = 0; i < 5; i++) {
    print('hello ${i + 1}');
  }
}