反射：从内部类获取模块镜像混合成单例对象

在以下情况下，如果将案例类定义为内部类，则无法找到案例类的伴随对象的apply方法：

case class Outer()

trait Foo {
  case class Inner()
}

object Bar extends Foo

迄今为止的做法：

import reflect.runtime.{currentMirror => cm, universe => ru}

def getApplyMethod[A: ru.TypeTag]: ru.MethodSymbol = {
  val sym     = ru.typeOf[A].typeSymbol
  val clazz   = sym.asClass
  val mod     = clazz.companionSymbol.asModule
  if (!mod.isStatic) println(s"Oh oh... $mod")  // and now?
  val im      = cm.reflect(cm.reflectModule(mod).instance)
  val ts      = im.symbol.typeSignature
  val mApply  = ts.member(ru.newTermName("apply")).asMethod
  mApply
}

getApplyMethod[Outer]
getApplyMethod[Bar.Inner]  // oh oh, detected, but what do to?

编译器的建议是：

object Inner is an inner module,
  use reflectModule on an InstanceMirror to obtain its ModuleMirror

因此， getApplyMethod唯一的信息就是TypeTag[Bar.Inner] ，我该怎么去解决这个问题呢？

---

请注意 ，这个问题是通过在Inner从特质中混合来引入的。 如果我有

object Bar { case class Inner() }

它工作正常， Inner模块是“静态”的。

---

问题是，如果类型是路径依赖的，TypeTag是否对路径进行编码？

因为从实例工作很容易：

scala> trait Foo { case class Inner(i: Int) }
defined trait Foo

scala> object Bar extends Foo
defined object Bar

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

scala> import universe._
import universe._

scala> currentMirror reflect Bar.Inner
res0: reflect.runtime.universe.InstanceMirror = instance mirror for Inner

scala> res0.symbol.typeSignature.member(newTermName("apply")).asMethod
res1: reflect.runtime.universe.MethodSymbol = method apply

scala> res0 reflectMethod res1
res3: reflect.runtime.universe.MethodMirror = method mirror for Foo.Inner.apply(i: scala.Int): Foo.this.Inner (bound to Inner)

scala> res3(7)
res4: Any = Inner(7)

用手从类型中获取封闭对象：

scala> typeOf[Bar.Inner]
res0: reflect.runtime.universe.Type = Bar.Inner

scala> val TypeRef(pre, sym, args) = res0
pre: reflect.runtime.universe.Type = Bar.type
sym: reflect.runtime.universe.Symbol = class Inner
args: List[reflect.runtime.universe.Type] = List()

scala> pre.typeSymbol.asClass.companionSymbol.asModule
res1: reflect.runtime.universe.ModuleSymbol = object Bar

scala> currentMirror reflectModule res1
res2: reflect.runtime.universe.ModuleMirror = module mirror for Bar (bound to null)

scala> res2.instance
res3: Any = Bar$@22a71ac

scala> currentMirror reflect res3
res4: reflect.runtime.universe.InstanceMirror = instance mirror for Bar$@22a71ac

scala> res4.symbol
res5: reflect.runtime.universe.ClassSymbol = object Bar

然后向下钻回Inner ：

scala> res5.typeSignature.member(newTermName("Inner"))
res7: reflect.runtime.universe.Symbol = object Inner

scala> res7.asModule
res9: reflect.runtime.universe.ModuleSymbol = object Inner

scala> res9.moduleClass
res10: reflect.runtime.universe.Symbol = object Inner

scala> res10.typeSignature
res11: reflect.runtime.universe.Type = 
scala.runtime.AbstractFunction1[scala.Int,Foo.this.Inner]
        with scala.Serializable {
  def <init>(): Foo.this.Inner.type
  final override def toString(): java.lang.String
  case def apply(i: scala.Int): Foo.this.Inner
  case def unapply(x$0: Foo.this.Inner): scala.Option[scala.Int]
  private def readResolve(): java.lang.Object
}

scala> res11.member(newTermName("apply"))
res12: reflect.runtime.universe.Symbol = method apply

或者使用sym ：

scala> res5.typeSignature.member(sym.name)
res16: reflect.runtime.universe.Symbol = class Inner

scala> res16.asClass.companionSymbol
res17: reflect.runtime.universe.Symbol = object Inner

scala> res17.typeSignature.member(newTermName("apply"))
res18: reflect.runtime.universe.Symbol = method apply

使用它：

scala> res4 reflectModule res9
res20: reflect.runtime.universe.ModuleMirror = module mirror for Foo.Inner (bound to Bar$@22a71ac)

scala> res20.instance
res22: Any = Inner

scala> currentMirror reflect res22
res23: reflect.runtime.universe.InstanceMirror = instance mirror for Inner

scala> res23 reflectMethod res18.asMethod
res24: reflect.runtime.universe.MethodMirror = method mirror for Foo.Inner.apply(i: scala.Int): Foo.this.Inner (bound to Inner)

scala> res24(7)
res25: Any = Inner(7)

链接地址: http://www.djcxy.com/p/76525.html

上一篇: Reflection: Getting module mirror from inner class mixed into a singleton object

下一篇: Finding enclosing instance (if any) by Scala reflection