Question

我正在尝试创建一个函数返回单元（这是为了实现一个RxScala观察器），但是当我将()添加到它的末尾时，我收到一个错误“应用程序不接受参数”。这是我的代码：

val client3MessageStreamObserver: Observable[Message] = client3.messageStream()
client3MessageStreamObserver.subscribe(
  m => println("Unexpected message received by client3"),
  // callback for handling exceptions
  t =>
    println("Ex client3: " + t)
// want to make this line work (which it doesn't) which is why 
// I need to be able to return Unit. 
//        client3TestPromise.success(true)
    ()     // error after adding Unit literal here.
)

添加()后为什么会出现此错误？如何摆脱它？如果我把它遗漏，我会收到错误提示“类型不匹配：预期（可投掷）=＆gt;单位，实际:(可投掷）=＆gt;任何）”。

Answer 1

试试这个：

val client3MessageStreamObserver: Observable[Message] = client3.messageStream()
client3MessageStreamObserver.subscribe(
  m => println("Unexpected message received by client3"),
  t => println("Ex client3: " + t)
 () => ()
)

第三个函数onCompleted是函数Unit => Unit。因此，参数为()，然后在返回时我们可以显式返回()或任何返回()的方法，例如println。

Answer 2

好的，所以我解决了这个问题。因为subscribe期望函数作为它的参数，所以我需要在括号中包含多个指令来创建一个代码块，即：

val client3MessageStreamObserver: Observable[Message] = client3.messageStream()
client3MessageStreamObserver.subscribe(
  // single instruction function doesn't require braces
  m => client3TestPromise.failure(new RuntimeException("Unexpected " +
      "message received by client3")),

  // multi-instruction function does require braces
  t => {
    println("Ex client3: " + t)
    client3TestPromise.success(true)
  }
)

如何从scala函数返回Unit？

2 个答案: