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class Test {
    import scala.collection._

    class Parent
    class Child extends Parent

    implicit val children = mutable.Map[String, Child]()

    def createEntities[T <: Parent](names: String*) = names.foreach(createEntity[T])


    def createEntity[T <: Parent](name: String)(implicit map: mutable.Map[String, T]): Unit = map.get(name) match {
        case None => println( name + " not defined.")
        case _ =>
    }
}

为什么编译器抱怨:

错误:找不到参数映射的隐式值:scala.collection.mutable.Map[String,T] names.foreach(createEntity[T])

?

4

1 回答 1

4

如果你调用,例如,createEntities[Parent]("A", "B")(你可以,因为Parent它是 的子类型Parent),它需要一个隐式的mutable.Map[String, Parent],并且没有。更准确地说,您的定义要求您mutable.Map[String, T]为 的每个子类型提供一个Parent,而不仅仅是那些已经定义的:

implicit def aMap[T <: Parent]: mutable.Map[String, T] = ...
于 2010-09-15T08:42:21.770 回答