gistfile1.txt

class Fruit {
  final String someString;

  Fruit(this.someString);

  void printString() {
    print(someString);
  }
}

String modString(String someString) {
  return "$someString + extra";
}

class Apple extends Fruit {
  Apple(String someString) : super(modString(someString));
}

void main() {
  var apple = Apple("This is an apple");
  apple.printString();
}