Scala:如何抑制未经检查的警告/正确执行地图的模式匹配? [英] Scala: How to suppress unchecked warnings / do pattern matching of maps correctly?

问题描述

在测试调用中返回一个 Option[Any] 的第三方函数.我知道如果这个函数返回一个 Map，它就是一个 Map[String, Any].在这种情况下，我想检查单个地图元素.

In a test call a third-party function which returns an Option[Any]. I know if this function returns a Map, it is a Map[String, Any]. In this case, I want to check for individual map elements.

theFunction(...) match {
  case Some(m: Map[String, Any]) =>
    m("some key") match {
      case some_condition => ... (my check)
    }
  case _ => fail("Invalid type")
}

但编译器警告 case Some(m: Map[String, Any]) 未选中.当我改用 Map[_,_] 时，编译器会在我检查 m("some key") 的时候退出.

But the compiler warns that case Some(m: Map[String, Any]) is unchecked. When I use Map[_,_] instead, the compiler bails out at the point where I check m("some key").

如何抑制此警告，或者更好:如何正确执行此检查?我能想到的唯一方法是

How do I suppress this warning, or better: how do I do this check correctly? The only approach I can think of is something like

theFunction(...) match {
  case Some(m: Map[_,_]) =>
    val m1: Map[String, Any] = m.toSeq.map(t => t._1.asInstanceOf[String] -> t._2).toMap
    m1("some key") match {
      case some_condition => ... (my check)
    }
}

但在我看来，这看起来很丑陋，并且引入了不必要的映射到 Seq 的转换，反之亦然.

but in my eyes, this looks ugly and introduces unnecessary converting of the map to a Seq and vice-versa.

推荐答案

目前没有办法在 Scala 中抑制这些警告.此处有一些关于该主题的有趣讨论.您可以忽略警告，或使用 asInstanceOf:

There is currently no way to suppress these warnings in Scala. There's some interesting discussion about the topic here. You can ignore the warning, or use asInstanceOf:

m.asInstanceOf[Map[String, Any]]("some key") match { ... }

这些类型的运行时操作容易出错，并且通常指向糟糕的类型系统.在极少数情况下，方法应该返回 Option[Any].在 Scala 中，几乎任何使用 Any 作为返回类型都是一个危险信号.

These types of runtime operations are error prone, and usually point to a poor type system. There are very few situations in which a method should return Option[Any]. Almost any use of Any as a return type is a red flag in Scala.

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