如何处理退货 [英] how do I process returned Either

问题描述

如果是scala函数，则

if a scala function is

def A(): Either[Exception, ArrayBuffer[Int]] = {
...
}

什么是处理返回结果的正确方法? val a = A() 和?

what should be the right way to process the returned result? val a = A() and ?

推荐答案

我通常更喜欢使用fold.您可以像地图一样使用它:

I generally prefer using fold. You can use it like map:

scala> def a: Either[Exception,String] = Right("On")

a.fold(l => Left(l), r => Right(r.length))
res0: Product with Either[Exception,Int] = Right(2)

或者您可以像模式匹配一​​样使用它:

Or you can use it like a pattern match:

scala> a.fold( l => {
     |   println("This was bad")
     | }, r => {
     |   println("Hurray! " + r)
     | })
Hurray! On

或者您可以像Option中的getOrElse一样使用它:

Or you can use it like getOrElse in Option:

scala> a.fold( l => "Default" , r => r )
res2: String = On

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