Scala：某些 UDT 上的运算符重载最小 "Type Class"？

Question

我正在尝试学习 scala "Type Class" 功能，但这是我失败的尝试。在此示例中，我尝试在 UDT 上创建可插入运算符：

package playground 

// my UDT
class Element(val value : Integer)

trait AdditiveOps {
    def +(e2: Element): Element
    def -(e2: Element): Element
}

// One possible implementation of AdditiveOps
class AdditiveOpsImpl(val e1: Element) extends AdditiveOps {
    def +(e2: Element): Element = {
      new Element(e1.value + e2.value)
    }

    def -(e2: Element): Element = {
      new Element(e1.value - e2.value)
    }
}

// What needs to be imported
object ElementOps {
  implicit def +(e1: Element) : AdditiveOps = {
    new AdditiveOpsImpl(e1)
  }

  implicit def -(e1: Element) : AdditiveOps = {
    new AdditiveOpsImpl(e1) 
  }
}

然后像这样使用它：

package playground 

object Main {
  import ElementOps._

  def main(args: Array[String]): Unit = {
    val e1 = new Element(2)
    val e2 = new Element(3)
    val e3 = e1 + e2

    println("Hello Class Types %s".format(e3.value))
  }
}

但我收到以下编译器错误：

type mismatch;  found   : e1.type (with underlying type playground.Element)  required: ?{def +(x: ? >: playground.Element): ?} Note that implicit conversions are not applicable because they are ambiguous:  both method + in object ElementOps of type (e1: playground.Element)playground.AdditiveOps  and method - in object ElementOps of type (e1: playground.Element)playground.AdditiveOps  are possible conversion functions from e1.type to ?{def +(x: ? >: playground.Element): ?}    Main.scala  /Playground/src/playground  line 9  Scala Problem

Answer 1

哦，发现问题了，它在我的 ElementOps 对象实现中。我需要：

object ElementOps {
   implicit def additive(e1: Element) : AdditiveOps = {
      new AdditiveOpsImpl(e1)
   }
}

基本上只实现一次隐式方法并以我喜欢的任何方式命名它，例如additive 但它可以是 whatever 并且不使用运算符。修复后，预期的输出是：Hello class types 5

Scala：某些 UDT 上的运算符重载最小 "Type Class"？

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