Scala - 使用案例类尝试获取 TypeTag 时没有可用的 TypeTag 异常? [英] Scala - No TypeTag Available Exception when using case class to try to get TypeTag?

问题描述

我正在查看 scala 反射 API，但我收到了很多异常.

I'm looking at the scala reflect API and I'm getting lots of exceptions.

文档参考:http://docs.scala-lang.org/overviews/reflection/environment-universes-mirrors.html

如何从泛型中获取 typetag?

How do I get the typetag from a generic?

  def getChildSettings[T: ru.TypeTag](path: String, settingsParameterObject: T) = {

    import scala.reflect.runtime.{ currentMirror => m }

    val m = ru.runtimeMirror(getClass.getClassLoader)
    val classC = ru.typeOf[T].typeSymbol.asClass
}

我得到一个例外:

No TypeTag available for ParameterObject.type

即使是一个非常简单的例子似乎也不起作用(编辑是的，它在 repl 中起作用)

Even a very simple example doesn't seem to work (edit yes it does in the repl)

import scala.reflect.runtime.universe._
import scala.reflect.runtime.currentMirror
import scala.reflect.runtime.{universe => ru}

def getTypeTag[T: ru.TypeTag](obj: T) = ru.typeTag[T]

case class ParameterObject(stringType: String, optionType: Option[String])

getTypeTag(ParameterObject)

我猜这与我调用方法的方式有关.

I'm guessing it's something about how I'm invoking the method.

推荐答案

我终于找到了问题所在.案例类必须在顶级定义 - 它们不能嵌套.这样的事情会失败.

I finally found out what the issue was. The case classes must be defined top level - they cannot be nested. Something like this would fail.

class Foo {
  describe("getSettings") {
    case class ParameterObject(foo: String)
    settings.getTypeTag(path, ParameterObject)
  }
}

class Clazzy {
      def getTypeTag[T: TypeTag](obj: T) = ru.typeTag[T]
}

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