Question

我希望能够做到：

object AddOrSubtract {
  def apply(x: Int, adding: Int) = x + adding
  def apply(x: Int, subtracting: Int) = x - subtracting
}

AddOrSubtract(1, adding = 5) // should be 6
AddOrSubtract(1, subtracting = 5) // should be -4

但我收到错误：

Error:(1331, 7) method apply is defined twice;
  the conflicting method apply was defined at line 1330:7
  def apply(x: Int, subtracting: Int) = x - subtracting

据我所知，这是因为这两种方法具有相同的签名。是否有一些模式可以解决这个问题？我唯一能想到的是使用隐式来改变值的类型，例如：

object AddOrSubtract {
  implicit class AddInt(val x: Int)
  implicit class SubInt(val x: Int)

  def apply(x: Int, adding: AddInt) = x + adding.x
  def apply(x: Int, subtracting: SubInt) = x - subtracting.x

  def run(): Unit = {
    AddOrSubtract(1, adding = 5)
    AddOrSubtract(1, subtracting = 5)
  }
}

但我很好奇是否有其他不那么不优雅的方式来实现这个目标？

Answer 1

您的示例代码可能会针对您的实际用例进行过度简化。如果是，则此解决方案将不适用。

object AddOrSubtract {
  def apply(x: Int, adding: Int=0, subtracting: Int=0) = x + adding - subtracting
}

AddOrSubtract(1, adding = 5)      // res0: Int = 6
AddOrSubtract(1, subtracting = 5) // res1: Int = -4

Answer 2

AFAIK没有好的解决方案。我能想象的唯一解决方法是

  object AddOrSubtract {
    def apply(x: Int, adding: Int = 0, subtracting: Int = 0) = 
      match (adding, subtracting) {
        case (0, 0) => throw Error("either adding or subtracting is required")
        case (x, 0) => x + adding
        case (0, x) => x - subtracting
       case (_, _) => throw Error("for now both adding and subtracting is not allowed")
   }

 AddOrSubtract(1, adding = 5) // should be 6
 AddOrSubtract(1, subtracting = 5) // should be -4

但它远非完美

同样方法的模式＆amp; scala中的参数相同但参数名称不同

2 个答案: