产量的scala表示类型不匹配

Question

Eclipse抛出异常：

type mismatch; found : scala.concurrent.Future[Any] required: scala.concurrent.Future[Boolean]

我在scala中比较新，所以我只需要返回一个布尔值，无论extractWord结果是否存在..

这段代码有什么问题？我误解了一些事情......

override def checkAccessAuthorized(implicit request: RequestHeader, context: ExecutionContext,sessionTimeoutInSeconds: Int): Future[Boolean] = {

      (for {
        word <- extractWord
      } yield for {
            Some(userId) <- cacheUtils.get(word)
            _ = cacheUtils.prolongTimeout(word, sessionTimeoutInSeconds)
        } yield {
         Future.successful(true)
      }).getOrElse {
        Future.successful(false)
      }
}

prolongTimeout方法的标题是：

def prolongTimeout(word: AuthenticityWord, timeoutInSeconds: Int)(implicit request: RequestHeader, context: ExecutionContext) : Unit