Question

假设

class SpecificAPI extends APIConnection{
   def annotate(...) = //definition of annotate function
}

我有一个班主任：

class Father{
   protected def processMessage[A<:APIConnection](recordToAnalyze: RecordToAnalyze, api:Option[A] = None): Option[IndexEnrichment]
}

class Child extends Father{
   override def processMessage[SpecificAPI](recordToAnalyze: RecordToAnalyze, api: Option[SpecificAPI]): Option[IndexEnrichment] = {

    api.get.annotate(...) //I cannot access to this function
}

为什么我无法访问Child类中SpecificAPI的方法？

基本上我想定义一个泛型方法来实例化与不同API的连接，我想只更改Children类中的函数processMessage。我错过了什么吗？

Answer 1

因为类SpecificAPI中的Child是类型参数。所以它与实际输入processMessage[A] ...

相同

你可能想要的是将类型参数提升到类定义，这样你就可以将SpecificApi传递给Child：

class Father[A<:APIConnection]{
   protected def processMessage(recordToAnalyze: RecordToAnalyze, api:Option[A] = None): Option[IndexEnrichment]
}

class Child extends Father[SpecificAPI]{
   override def processMessage(recordToAnalyze: RecordToAnalyze, api: Option[SpecificAPI]): Option[IndexEnrichment] = {

    api.get.annotate(...) //I cannot access to this function
}

作为旁注，请不要直接在Option上使用get，除非你只是为了做这个例子。

Answer 2

SpecificAPI类的processMessage中的类型参数Child是一个无约束的类型参数，名称极其混乱。如果您想更好地了解代码的作用，请将其重命名为X：

class Child extends Father{
  override def processMessage[X](
    recordToAnalyze: RecordToAnalyze, 
    api: Option[X]
  ): Option[IndexEnrichment] = {
    api.get.annotate(...) //I cannot access to this function
    // Well, why should an arbitrary `X` have method `annotate`?
  }
}

现在很明显，这无法编译。

我有一种模糊的感觉，你可能有这样的意思：

trait APIConnection
class IndexEnrichment
class RecordToAnalyze

class SpecificAPI extends APIConnection {
  def annotate(): Unit = ???
}

trait Father [A <: APIConnection] {
  protected def processMessage(
    recordToAnalyze: RecordToAnalyze, 
    api:Option[A] = None
  ): Option[IndexEnrichment]
}

class Child extends Father[SpecificAPI] {
  override def processMessage(
    recordToAnalyze: RecordToAnalyze, 
    api: Option[SpecificAPI]
  ): Option[IndexEnrichment] = {
    api.get.annotate()
    ???
  }
}

scala：类之间函数的上限和下限

2 个答案: