通过给定的泛型类型Scala获取类的伴随对象 [英] Get companion object of class by given generic type Scala

问题描述

我想做的是创建一个函数，它将采用一个通用类并在其中使用一个静态方法（对于Java语言，我的意思是它的伴体对象的方法）。

What I am trying to do is to make a function that would take a generic class and use a static method in it (sorry for Java language, I mean method of its companion object).

trait Worker {def doSth: Unit}

class Base

object Base extends Worker

// this actually wouldn't work, just to show what I'm trying to achieve
def callSthStatic[T that companion object is <: Worker](implicit m: Manifest[T]) {
  // here I want to call T.doSth (on T object)
  m.getMagicallyCompanionObject.doSth
}

任何想法？

推荐答案

Miles Sabin的一个提示可能会给你一个提示：

A gist by Miles Sabin may give you a hint:

trait Companion[T] {
  type C
  def apply() : C
}

object Companion {
  implicit def companion[T](implicit comp : Companion[T]) = comp()
}

object TestCompanion {
  trait Foo

  object Foo {
    def bar = "wibble"

    // Per-companion boilerplate for access via implicit resolution
    implicit def companion = new Companion[Foo] {
      type C = Foo.type
      def apply() = Foo
    }
  }

  import Companion._

  val fc = companion[Foo]  // Type is Foo.type
  val s = fc.bar           // bar is accessible
}

使用 -Ydependent-method-types 标志编译如果使用Scala 2.9.x。

This should be compiled with the -Ydependent-method-types flag if using Scala 2.9.x.

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