做一些N次或直到Scala满足条件 [英] Do something up to N times or until condition is met in Scala

问题描述

我有一些Scala代码应该为网络服务查询某个标记，然后将该标记与预期标记进行比较。我希望继续查询预期的令牌，直到找到它，或者直到我尝试了N次尝试失败为止。

以下是如何在Java-tacular时尚：

  def keepLo​​oking（expectedToken：String，maxTries：Int）{
 var attempts = 0 
 var token =
 do {
 Thread.sleep（试试* 1000）//不要通过调用太快来压倒服务！ （尝试< = maxTries&&& token！= expectedToken）
 
 token = makeSomeNetworkCall（）
 tries + = 1 
} b  

我想在功能上做得更多。我有一个想法：

  1.to（maxTries）map {tryNum => 
 Thread.sleep（tryNum  -  1 * 1000）//不要通过调用太快来压倒服务！ 
 makeSomeNetworkCall（）
}存在（_ == expectedToken）
  

提出了两个问题：
$ b $ ol

map 是懒惰的，所以存在应该将它短路，对吧？如果我在第二次通话中找到我的代币，我不想进行10次网络通话。

有没有更符合我个人喜好的习惯？

解决方案

回答1：

<$ c $如果您将范围转换为流，则 （1到10）.toStream map（i => {println（i）; i}）exists（_ == 2）（b =

  ）
 //将打印
 // 1 
 // 2 
  

I have some Scala code that should query a network service for a certain token, then compare that token to an expected one. I want to keep querying for the expected token until I find it, or until I've made N unsuccessful attempts.

Here's how it could be done in a Java-tacular fashion:

def keepLooking(expectedToken: String, maxTries: Int) {
  var tries = 0
  var token = ""
  do {
    Thread.sleep(tries * 1000) // don't overwhelm the service by calling it too fast!

    token = makeSomeNetworkCall()
    tries += 1
  } while (tries <= maxTries && token != expectedToken)
}

I'd like to do it more functionally. I have one idea:

1.to(maxTries) map { tryNum =>
  Thread.sleep(tryNum - 1 * 1000) // don't overwhelm the service by calling it too fast!
  makeSomeNetworkCall()
} exists (_ == expectedToken)

But this raises two questions:

1. map is lazy, so exists should short circuit it, right? I don't want to make 10 network calls if I find my token on the second call.
2. Is there a more idiomatic way to achieve what I want?

解决方案

Answer to 1.:

map is only lazy if you convert the Range to a Stream:

(1 to 10).toStream map (i => { println(i); i }) exists (_ == 2)
// will print
// 1
// 2

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