dart_state_repo.dart

abstract class State {}

class StateA implements State {
  StateA({this.name = "Hello"});
  final String name;
}

class StateB implements State {}

class StateHandlerNotWorking {
  StateHandlerNotWorking({this.state});
  
  final State state;
  
  void update() {
    if (state is StateA) {
      print(state.name);
    }
  }
}

class StateHandlerWorking {
  StateHandlerWorking({this.state});
  
  final State state;
  
  void update() {
    final state = this.state;
    
    if (state is StateA) {
      print(state.name);
    }
  }
}

void main() {}