NoSwitch.cs

static State ChangeState(State current, Transition transition, bool hasKey)
{
  if (current == Opened && transition == Close)
    return Closed;
  else if (current == Closed && transition == Open)
    return Open;
  else if (current == Closed && transition == Lock && hasKey)
    return Locked;
  else if (current == Locked && transition == Unlock && hasKey)
    return Closed;
  else
    throw new InvalidOperationException($"Invalid transition");
}