scala - 在 Scala 中分解函数

Question

所以我有以下函数定义。

def partition[A, B, C](
    partitionF: A => Either[B, C])

其中 A、B 和 C 是任意类型。

现在我定义一个函数传入

sealed trait Response
case object ThisResponse extends Response
case object ThatResponse extends Response

case object ThisDirection
case object ThatDirection

def responsePartition(response: Response): 
    Either[ThisDirection, ThatDirection] = response match {
  case ThisResponse => Left(ThisDirection)
  case ThatResponse => Right(ThatDirection)
}

然后我们将按如下方式传入

partition(responsePartition)

在业务逻辑中。

现在我试图单独获取在 responsePartition 中定义的 A => B 和 A => C 方法

所以我要找的是

val partitionFonB : A => B = ??? // This is case of this example would be ThisResponse => ThisDirection

和

val partitionFonC : A => C = ??? // This is case of this example would be ThatResponse => ThatDirection

有没有办法做到这一点？我尝试了右投影和左投影，但无法获得正确的类型。

Answer 1

在一般情况下，您不能从 A => 类型的函数中提取(总的)A => B 或 A => C 函数要么 [B, C]。如果函数为特定值 a1 生成 B，则 A => C 函数不会在那里定义，反之亦然。

你能做的最好，如果你只有 A => Either[B, C] 是 A => Option[B] 和 A = > 选项[C](使用_.toLeft.toOption 和_.toOption)。

对于您的特定情况，您可以提取 ThisResponse => ThisDirection 和 ThatResponse => ThatDirection 作为单独的函数开始，然后将它们组合起来以获得 Response => Either[ThisDirection, ThatDirection] 函数:

def thisResponse(response: ThisResponse): ThisDirection = ThisDirection // or any This-specific functionality

def thatResponse(response: ThatResponse): ThatDirection = ThatDirection // or any That-specific functionality

def responsePartition(response: Response): 
    Either[ThisDirection, ThatDirection] = response match {
  case r:ThisResponse => Left(thisResponse(r))
  case r:ThatResponse => Right(thatResponse(r))
}