Question

当它是一个嵌套类型时，我无法通过其密封超级特征的反射来恢复单例实例：

import reflect.runtime.universe._
import reflect.runtime.{currentMirror => cm}

object Foo {
  case object Bar extends Foo
}
sealed trait Foo

def getModule(tpe: Type): Any = {
  val classSymbol  = tpe.typeSymbol.asClass
  val compSymbol   = classSymbol.companionSymbol  // gives <none> !
  val moduleSymbol = compSymbol.asModule
  val moduleMirror = cm.reflectModule(moduleSymbol)
  moduleMirror.instance
}

val subs     = typeOf[Foo].typeSymbol.asClass.knownDirectSubclasses
val tpeOther = subs.last.asType.toType

val res = getModule(tpeOther)
println(res)

对companionSymbol的调用产生“无”，asModule失败并带有

scala.ScalaReflectionException: <none> is not a module

（我从Eugene Burmako的this Gist身上取走了身体。）

如果您更改为

sealed trait Foo
case object Bar extends Foo  // not nested in object Foo

它有效......

Answer 1

这还不是答案，但也许是一种解决方法，以防它对任何人都有帮助。

它第一次对我有用，但不是第二次，因为复制结果不是科学吗？：

scala> res22.head
res24: reflect.runtime.universe.Symbol = object Bar

scala> .asClass
res25: reflect.runtime.universe.ClassSymbol = object Bar

scala> .isModule
isModule        isModuleClass   

scala> .isModuleClass
res26: Boolean = true

scala> res25.companionSymbol
res27: reflect.runtime.universe.Symbol = object Bar

scala> .isModule
res28: Boolean = true

让我查一下：

scala> cm reflectModule res27.asModule
res30: reflect.runtime.universe.ModuleMirror = module mirror for Foo.Bar (bound to null)

scala> .instance
res31: Any = Bar

复制每个命令确实有效，所以不是竞争条件：

scala> typeOf[Foo].typeSymbol.asClass.knownDirectSubclasses.head
res29: reflect.runtime.universe.Symbol = object Bar

scala> .asClass
res30: reflect.runtime.universe.ClassSymbol = object Bar

scala> .companionSymbol
res31: reflect.runtime.universe.Symbol = object Bar

scala> .asModule
res32: reflect.runtime.universe.ModuleSymbol = object Bar

有些东西被初始化了，但我还没看到什么。我注意到我这样做了：

scala> cm reflect Foo
res13: reflect.runtime.universe.InstanceMirror = instance mirror for Foo$@3a854a76

嗯，这是一个成绩单，在你去的时候调用typeSig：

scala> import reflect.runtime.universe._
import reflect.runtime.universe._

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

scala> :pa
// Entering paste mode (ctrl-D to finish)

sealed trait Foo
object Foo {
  case object Bar extends Foo
}

// Exiting paste mode, now interpreting.

defined trait Foo
defined object Foo

scala> typeOf[Foo].typeSymbol
res0: reflect.runtime.universe.Symbol = trait Foo

scala> res0.typeSignature
res1: reflect.runtime.universe.Type = scala.AnyRef

scala> res0.asClass
res2: reflect.runtime.universe.ClassSymbol = trait Foo

scala> .companionSymbol
res3: reflect.runtime.universe.Symbol = object Foo

scala> .typeSignature
res4: reflect.runtime.universe.Type = Foo.type

scala> res2.knownDirectSubclasses.head.asClass
res5: reflect.runtime.universe.ClassSymbol = object Bar

在这种情况下不需要这个：

scala> res5.typeSignature
res6: reflect.runtime.universe.Type = 
scala.AnyRef
        with Foo
        with scala.Product
        with scala.Serializable {
  def <init>(): Foo.Bar.type
  override def productPrefix: java.lang.String
  def productArity: scala.Int
  def productElement(x$1: scala.Int): scala.Any
  override def productIterator: Iterator[scala.Any]
  def canEqual(x$1: scala.Any): scala.Boolean
  override def hashCode(): scala.Int
  override def toString(): java.lang.String
  private def readResolve(): java.lang.Object
}

scala> res5.companionSymbol
res7: reflect.runtime.universe.Symbol = object Bar

scala> res7.isModule
res8: Boolean = true

scala> cm reflectModule res7.asModule
res9: reflect.runtime.universe.ModuleMirror = module mirror for Foo.Bar (bound to null)

scala> .instance
res10: Any = Bar

也许我们已经够大了，难以记住this bug.

为了完整性而非关闭：

object Driller extends App {
  def getModule(sym: Symbol): Any = {
    val classSymbol = sym.asClass
    val compSymbol = classSymbol.companionSymbol // gives <none> !
    val moduleSymbol = compSymbol.asModule
    val moduleMirror = cm.reflectModule(moduleSymbol)
    moduleMirror.instance
  }
  val foo = typeOf[Foo].typeSymbol.asClass
  foo.typeSignature
  foo.companionSymbol.typeSignature
  val bar = foo.knownDirectSubclasses.head.asClass
  val res = getModule(bar)
  println(res)
}

当类型嵌套时，通过密封超级特征的反射恢复单例实例

1 个答案: