删除 Scala 中的"eliminated by erasure"警告

Question

我有一个简单的Scala函数，它从Map[String, Any]生成Json文件。

  def mapToString(map:Map[String, Any]) : String = {
    def interpret(value:Any)  = {
      value match {
        case value if (value.isInstanceOf[String]) => """ + value.asInstanceOf[String] + """
        case value if (value.isInstanceOf[Double]) => value.asInstanceOf[Double]
        case value if (value.isInstanceOf[Int]) => value.asInstanceOf[Int]
        case value if (value.isInstanceOf[Seq[Int]]) => value.asInstanceOf[Seq[Int]].toString.replace("List(", "[").replace(")","]")
        case _ => throw new RuntimeException(s"Not supported type ${value}")
      }
    }
    val string:StringBuilder = new StringBuilder("{n")
    map.toList.zipWithIndex foreach {
      case ((key, value), index) => {
        string.append(s"""  "${key}": ${interpret(value)}""")
        if (index != map.size - 1) string.append(",n") else string.append("n")
      }
    }
    string.append("}n")
    string.toString
  }

此代码运行良好，但在编译过程中会发出警告消息。

Warning:(202, 53) non-variable type argument Int in type Seq[Int] (the underlying of Seq[Int]) 
is unchecked since it is eliminated by erasure
        case value if (value.isInstanceOf[Seq[Int]]) => 
value.asInstanceOf[Seq[Int]].toString.replace("List(", "[").replace(")","]")
                                                ^

case value if (value.isInstanceOf[Seq[Int]])行引起警告，我尝试case value @unchecked if (value.isInstanceOf[Seq[Int]])删除警告，但它不起作用。

如何删除警告？

Answer 1

如果你真的不关心组件类型（似乎你不关心，因为你所做的只是字符串）：

case value if (value.isInstanceOf[Seq[_]]) => 
    value.asInstanceOf[Seq[_]].toString.replace("List(", "[").replace(")","]")

仔细想想，你应该可以在任何事情上调用toString：

case value if (value.isInstanceOf[Seq[_]]) => 
    value.toString.replace("List(", "[").replace(")","]")

但考虑Seq#mkString ，而不是toString然后扰乱字符串

value.mkString("[", ",", "]")

最后，模式isInstanceOf/asInstanceOf可以由匹配（在所有情况下）代替

case value: Int => value    // it's an Int already now, no cast needed 
case value: Seq[_] => value.mkString("[", ",", "]")

Answer 2

您可以执行以下操作，

case value: String => ???
case value: Double => ???
case value: Int => ???
case value: Seq[Int] @unchecked => ???

或者正如@Thilo提到的

case value: Seq[_] => 

Answer 3

这是一个更好的代码，它不会生成警告消息（带有Thilo&Łukasz的提示）。

  def mapToString(map:Map[String, Any]) : String = {
    def interpret(value:Any)  = {
      value match {
        case value:String => """ + value + """
        case value:Double => value
        case value:Int => value
        case value:Seq[_] => value.mkString("[",",","]")
        case _ => throw new RuntimeException(s"Not supported type ${value}")
      }
    }
    map.toList.map { case (k, v) => s"""  "$k": ${interpret(v)}""" }.mkString("{n", ",n", "n}n")
  }