Scala:如何避免在这里使用var [英] Scala: How to avoid var here

问题描述

我有一个这样的代码段:

I have a code snippet like this:

def until(terminationCond: List[A]=>Boolean, combiner: List[A]=>List[A] )(obj: List[A]): A = {
      var tempObj = obj
      while(!terminationCond(tempObj)) {
          tempObj = combiner(obj)
      }
    tempObj.head
    }

我正在寻找一种以功能编程样式编写此代码的方法，从而避免使用任何 mutable 类型.

I am looking out a way to write this code from functional programming style, avoiding any mutable types.

推荐答案

我发现以下内容比显式递归版本更具声明性:

I find the following a little more declarative than the explicitly recursive version:

def until[A](
  terminationCond: List[A] => Boolean,
  combiner: List[A] => List[A]
)(obj: List[A]): A =
  Stream.iterate(obj)(combiner).dropWhile(!terminationCond(_)).head.head

即我们通过迭代地应用combiner来创建结果流，只要不满足终止条件就将其丢弃，然后返回它所针对的第一个对象的头部.

I.e. we create a stream of results by iteratively applying combiner, drop as long as the termination condition doesn't hold, and then return the head of the first for which it does.

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