Question

我有两个类似方法的对象〜（...）。我还定义了隐式转换，它应该将pair（String，A）转换为DemoObject或WopWopWop

class DemoObject[A](t: (String, A)) {
  def ~(t: (String, A)) = "demo"
}

class WopWopWop[A](t: (String, A)) {
  def ~(t: AnyVal) = "wop wop wop"
}

object ImplicitDemoConversions {
  implicit def pair2DemoObject[A](t: (String, A)) = new DemoObject(t)
}

object ImplicitWopWopWopConversions {
  implicit def pair2WopWopWop[A](t: (String, A)) = new WopWopWop(t)
}

然而，有点像

import ImplicitDemoConversions._
object Hello {
  def main(args: Array[String]): Unit = {
    import ImplicitWopWopWopConversions._
    val pair = ("LolTest" -> "A") ~ ("whoa" -> "wop wop wop")

    println(pair) 
  }
}

将打印回答演示，而不是预期 wop wop wop 。看起来scala编译器会忽略ImplicitWopWopWopConversions的第二次导入._

问题是为什么我认为（String，String）对应该转换为 WopWopWop ，我如何获得WopWopWop对象而不是DemoObject？

你可以在https://github.com/json4s/json4s/issues/121

找到真实的例子

Answer 1

您可以使用别名隐藏导入。

import ImplicitDemoConversions.{pair2DemoObject => i}
object Hello {
  def main(args: Array[String]): Unit = {
    import ImplicitWopWopWopConversions.{pair2WopWopWop => i}
    val pair = ("LolTest" -> "A") ~ ("whoa" -> "wop wop wop")

    println(pair) 
  }
}

修改

您的元组转换为DemoObject而不是WopWopWop的原因是因为DemoObject＆n; ~方法参数类型比WopWopWop＆＃39; S

就像这个例子一样：

object A { def m(x: AnyVal) { println(x) } def m(x: (Int, String)) { println(x) } // This will call the first method, because the second method can't be // applied to an Int a(1) // Either method could be applied to a (Int, String), but the second // method will be chosen, because it's argument type is more specific. a((1 -> "hello")) }

Scala隐式转换顺序

1 个答案: