Abstract Class example

login_state.dart

abstract class LoginState {}

class LoginLoadingState extends LoginState{}
class LoginSuccessState extends LoginState{}  
class LoginFailureState extends LoginState{}

void handleLoginState(LoginState state) {
  switch(state) {
     case LoginLoadingState():
      print('Logging in...'); // Handle loading state
      break;
    case LoginSuccessState():
      print('Welcome'); // Handle success state
      break;
    case LoginFailureState():
      print('Error'); // Handle failure state
      break;
  }
}

  
void main() {
  handleLoginState(LoginLoadingState()); 
  handleLoginState(LoginSuccessState()); 
  handleLoginState(LoginFailureState());
}