Types Promotion: Dart vs Swift

main.dart

void main() {}

abstract class Shape {}

class Square implements Shape {
  String? id;
}

class Circle implements Shape {
  String? name;
}

class Rectangle implements Shape {
  String? desc;
}

class Option {
  String? id;
  Shape? shape;
}

// It works. Dart can figure out types (subtypes).
void printShape(Shape shape) {
  if (shape is Square) {
    print(shape.id);
  } else if (shape is Circle) {
    print(shape.name);
  } else if (shape is Rectangle) {
    print(shape.desc);
  }
}

// It doesn't work. Dart can't figure out a type.
void printOptions(Option option) {
  if (option.shape is Square) {
    if (option.shape != null) {
      print(option.shape!.id);
    }
  } else if (option.shape is Circle) {
    if (option.shape != null) {
      print(option.shape!.name);
    }
  } else if (option is Rectangle) {
    if (option.shape != null) {
      print(option.shape!.desc);
    }
  }
}