Dart可变参数，命名参数

void main() {
  for (int i = 0; i < 5; i++) {
    print('hello ${i + 1}');
  }
  show_info("Tom");
  show_info("Lucy", 20);
  show_info2("Cat");
  show_info2("Mouse", age:10, sex:'femail');
}

void show_info(String name, [int? age]) {
  if (age != null) {
    print("name:$name, age:$age");
  } else {
    print("name:$name");
  }
}

void show_info2(String name, {int? age, String sex='male'}) {
  if (age != null) {
    print("name:$name, age:$age, sex:$sex");
  } else {
    print("name:$name, sex:$sex");
  }
}