unnamed_factory.dart

final _alreadyCreatedCircleInstances = Map<int, Circle>();

class Circle {
  final int size;
  Circle._(this.size);

  factory Circle(int size) {
    _alreadyCreatedCircleInstances[size] = _alreadyCreatedCircleInstances[size] ?? Circle._(size);
    return _alreadyCreatedCircleInstances[size]!;
  }
}

void main(){
    var c1 = Circle(40);
    var c2 = Circle(40);
    print("${c1 == c2}");
}