类型标签在代码块范围内不起作用? [英] Typetags not working inside of code block scope?

问题描述

好的，所以我遇到这个问题的真正原因是我的 ScalaTests 无法编译，因为我在测试范围内定义了一些类，这些类调用另一个期望与 TypeTags 一起使用的类文件.请注意，因为 B 类在我的测试"中(假设这是一个 Scala 测试调用)，因此 typetag 不再可行.我怀疑也许我不应该在本地范围内的匿名类上尝试这个，但是有人可以帮我理解吗?谢谢

import scala.reflect.runtime.universe._导入 scala.Symbol类 TypeTagger[T:TypeTag] {val tt = typeTag[T]}对象类型标签{def apply[T]()(implicit tt:TypeTag[T]) = new TypeTagger[T]}对象 TestRunTypeTagger 扩展应用程序 {A级val 测试 = 新的 TypeTagger[A]{B级val test2 = TypeTagger[B]()//失败}}

错误:没有可用于 B 的 TypeTagval test2 = TypeTaggerB

<块引用>

 ^ 方法的参数不足:(隐式 tt:

reflect.runtime.universe.TypeTag[B])chorle.scala.testarea.TypeTagger[B]在对象 TypeTagger 中.未指定值参数 tt.val test2 = TypeTaggerB

<代码> ^

解决方案

它似乎适用于 WeakTypeTag 而不是 TypeTag(也改变 typeTag 到 weakTypeTag).我真的不知道为什么；找不到任何关于此的具体文档.

Ok so the real reason I ran into this is that my ScalaTests failed to compile, because I defined some of the classes inside of the test scope that call another class file expecting to work with TypeTags. Notice that because class B is within my "test" (pretend this is a scala test call) , typetag no longer becomes viable. I suspect maybe I shouldn't be attempting this on an anonymous class inside of a local scope, but could someone help me understand please? Thanks

import scala.reflect.runtime.universe._
import scala.Symbol


class TypeTagger[T:TypeTag] {
  val tt = typeTag[T]
}

object TypeTagger {
  def apply[T]()(implicit  tt:TypeTag[T]) = new TypeTagger[T]
}

object TestRunTypeTagger extends App {
  class A

  val test = new TypeTagger[A]

  {
    class B
    val test2 = TypeTagger[B]()    //fails
  }
}

Error: No TypeTag available for B val test2 = TypeTaggerB

                       ^ not enough arguments for method apply: (implicit tt:

reflect.runtime.universe.TypeTag[B])chorle.scala.testarea.TypeTagger[B] in object TypeTagger. Unspecified value parameter tt. val test2 = TypeTaggerB

                         ^

解决方案

It seems to work with a WeakTypeTag instead of a TypeTag (also change typeTag to weakTypeTag). I have no idea why really; couldn't find any documentation about this specifically.

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