一种状态机转换写法

kudu中tablet replica的状态机为：

// NOT_INITIALIZED -> INITIALIZED -> BOOTSTRAPPING -> RUNNING -> STOPPING -> STOPPED -> SHUTDOWN
//             |              |                |                  ^ ^ ^
//             |              |                |                  | | |
//             |              |                +------------------+ | |
//             |              +-------------------------------------+ |
//             +------------------------------------------------------+

代码如下：

void TabletReplica::set_state(TabletStatePB new_state) {
  switch (new_state) {
    case NOT_INITIALIZED:
      LOG(FATAL) << "Cannot transition to NOT_INITIALIZED state";
      return;
    case INITIALIZED:
      CHECK_EQ(NOT_INITIALIZED, state_);
      break;
    case BOOTSTRAPPING:
      CHECK_EQ(INITIALIZED, state_);
      break;
    case RUNNING:
      CHECK_EQ(BOOTSTRAPPING, state_);
      break;
    case STOPPING:
      CHECK_NE(STOPPED, state_);
      CHECK_NE(SHUTDOWN, state_);
      break;
    case STOPPED:
      CHECK_EQ(STOPPING, state_);
      break;
    case SHUTDOWN: FALLTHROUGH_INTENDED;
    case FAILED:
      CHECK_EQ(STOPPED, state_) << TabletStatePB_Name(state_);
      break;
    default:
      break;
  }
  state_ = new_state;
}