本文介绍了理解`andThen`的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我遇到了andThen，但没有正确理解.
I encountered andThen, but did not properly understand it.
为了进一步研究，我阅读了 Function1.andThen 文档
To look at it further, I read the Function1.andThen docs
def andThen[A](g: (R) ⇒ A): (T1) ⇒ A
mm 是一个 MultiMap 实例.
scala> mm
res29: scala.collection.mutable.HashMap[Int,scala.collection.mutable.Set[String]] with scala.collection.mutable.MultiMap[Int,String] =
Map(2 -> Set(b) , 1 -> Set(c, a))
scala> mm.keys.toList.sortWith(_ < _).map(mm.andThen(_.toList))
res26: List[List[String]] = List(List(c, a), List(b))
scala> mm.keys.toList.sortWith(_ < _).map(x => mm.apply(x).toList)
res27: List[List[String]] = List(List(c, a), List(b))
注意 - 来自 DSLs in Action
andThen 强大吗?基于这个例子，它看起来像 mm.andThen de-sugars to x =>mm.apply(x).如果andThen还有更深的含义，那我还没看懂.
Is andThen powerful? Based on this example, it looks like mm.andThen de-sugars to x => mm.apply(x). If there is a deeper meaning of andThen, then I haven’t understood it yet.
推荐答案
andThen 只是函数组合.给定一个函数 f
andThen is just function composition. Given a function f
val f: String => Int = s => s.length
andThen 创建一个新函数，它应用 f 后跟参数函数
andThen creates a new function which applies f followed by the argument function
val g: Int => Int = i => i * 2
val h = f.andThen(g)
h(x) 然后是 g(f(x))
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