Scala-'for-yield'子句在某些情况下不会产生任何收益吗? [英] Scala - can 'for-yield' clause yields nothing for some condition?

问题描述

在Scala语言中，我想编写一个在给定范围内产生奇数的函数.该函数在迭代偶数时会打印一些日志.该函数的第一个版本是:

In Scala language, I want to write a function that yields odd numbers within a given range. The function prints some log when iterating even numbers. The first version of the function is:

def getOdds(N: Int): Traversable[Int] = {
  val list = new mutable.MutableList[Int]
  for (n <- 0 until N) {
    if (n % 2 == 1) {
      list += n
    } else {
      println("skip even number " + n)
    }
  }
  return list
}

如果我省略打印日志，则实现变得非常简单:

If I omit printing logs, the implementation become very simple:

def getOddsWithoutPrint(N: Int) =
  for (n <- 0 until N if (n % 2 == 1)) yield n

但是，我不想错过记录部分.如何更紧凑地重写第一个版本?如果可以像这样重写它，那就太好了

However, I don't want to miss the logging part. How do I rewrite the first version more compactly? It would be great if it can be rewritten similar to this:

def IWantToDoSomethingSimilar(N: Int) =
  for (n <- 0 until N) if (n % 2 == 1) yield n else println("skip even number " + n)

推荐答案

def IWantToDoSomethingSimilar(N: Int) = 
  for {
    n <- 0 until N
    if n % 2 != 0 || { println("skip even number " + n); false }
  } yield n

使用filter代替for表达式会更简单.

Using filter instead of a for expression would be slightly simpler though.

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