Dart types in action

types_playground.dart

class Car {
  start() {}
}

class Mustang extends Car {
  startGasEngine() {
    print('Starting gas engine.');
  }

  openWindow() {}
}

class ModelS extends Car {
  startElectricEngine() {
    print('Starting electric engine.');
  }

  openWindow() {}
}

Car getCart(bool x) {
  if (x) {
    return new Mustang();
  }

  return new ModelS();
}

void addCar(List<Car> cars, Car car) {
  cars.add(car);
}

void main(List<String> args) {

  Car car = getCart(args[0] == 'mustang');

  // dartanalyzer: The method 'startGasEngine' is not defined for the class 'Car'
  // But it will run just fine.
  car.openWindow();

  // dartanalyzer: no issue
  // Runtime will fail (`dart main.dart mustang`).
  ModelS m = car;
  m.startElectricEngine();


  // dartanalyzer: no issue
  // Runtime fail.
  List<Mustang> cars = [];
  addCar(cars, new ModelS());
  cars[0].startGasEngine();
}