如何使用Scala反射递归访问对象的所有公共成员？

Question

我不知道如何在不知道/指定其类型的情况下如何访问对象成员RECURSIVELY.在我的情况下,问题仅限于我想要访问的lazy vals和object成员.对象可以嵌套到lazy vals存在于其中的任何深度.例如:

object TestShallow {
  lazy val value1 = 1
}

object TestDeep {
  lazy val value1 = 1

  object NestedObj {
    lazy val value2 = 2
  }
}

这是我到目前为止:

import scala.reflect.ClassTag
import scala.reflect.runtime.universe._

  def evalMemberValues[A: TypeTag](topLevelObj: A)(implicit c: ClassTag[A]): Unit = {
    val mirror = runtimeMirror(getClass.getClassLoader)

    def loop[B: TypeTag](obj: B)(implicit c: ClassTag[B]): Unit = {
      println(s"INSPECTING: $obj: ${typeOf[B]}")
      val members = typeOf[B].decls.filter(_.isPublic)
      members.foreach { m =>
        if(m.isTerm && m.isModule) {
          println(s"MODULE: $m")
          // THE PROBLEM IS HERE !!!:
          val inst = mirror.reflectModule(m.asModule).instance // type is Any
          loop(inst)
        }
        else if(m.isTerm && ! m.isConstructor && m.isMethod && m.typeSignature.paramLists.isEmpty && ! m.typeSignature.takesTypeArgs) {
          val im = mirror.reflect(obj)
          val value = im.reflectMethod(m.asMethod)()
          println(s"VAL/DEF: $m = $value")
        }
        else {
          println(s"OTHERS: $m")
        }
      }
    }

    loop(topLevelObj)
  }

它适用于第一级声明:

scala> evalMemberValues(TestShallow)
INSPECTING: $line7.$read$$iw$$iw$$iw$$iw$TestShallow$@1669f4e5: TestShallow.type
OTHERS: constructor TestShallow
VAL/DEF: lazy value value1 = 1

但是,它无法正确递归:

scala> evalMemberValues(TestDeep)
INSPECTING: $line11.$read$$iw$$iw$$iw$$iw$TestDeep$@3c2f310c: TestDeep.type
OTHERS: constructor TestDeep
VAL/DEF: lazy value value1 = 1
MODULE: object NestedObj
INSPECTING: $line11.$read$$iw$$iw$$iw$$iw$TestDeep$NestedObj$@4f1f2f84: Any
OTHERS: method ==
OTHERS: method !=
OTHERS: method equals
OTHERS: method hashCode
OTHERS: method toString
OTHERS: method getClass
OTHERS: method isInstanceOf
OTHERS: method asInstanceOf
OTHERS: method ##

正如您所看到的问题在于这一行:

val inst = mirror.reflectModule(m.asModule).instance

因为它给了我一个类型的实例,Any信息丢失了.理想情况下,我会得到一个实例,TypeTag并提供与之ClassTag对应的正确类型的详细信息m.我没有找到如何从中获取Symbol,这m就是,我猜编译器不会生成它.我也没看到如何使用它instanceOf[_].也许我可以通过其他方式获得声明/成员？我发现的所有示例都没有动态获取实例类型,也没有在实例上递归以获得下一级声明.

此外,有什么更好的办法来检查Symbol是val或lazy val？我只看到在这样的检查ModuleSymbol:isVal,isLazy这是一种怪我.

Answer 1

This works for me:

  import scala.reflect.runtime.universe._

  def evalMemberValues[A](topLevelObj: A)(implicit c: TypeTag[A]): Unit = {

    val mirror = runtimeMirror(getClass.getClassLoader)

    def loop(obj: Any, tp: Type): Unit = {
      println(s"INSPECTING: $tp:")
      val objMirror = mirror.reflect(obj)
      val members = tp.decls.filter(_.isPublic)
      members.foreach { m =>
        if (m.isTerm && m.isModule) {
          println(s"MODULE: $m")
          loop(mirror.reflectModule(m.asModule).instance, m.info)
        }
        else if (m.isTerm && !m.isConstructor && m.isMethod && m.typeSignature.paramLists.isEmpty && !m.typeSignature.takesTypeArgs) {
          val value = objMirror.reflectMethod(m.asMethod)()
          println(s"VAL/DEF: $m = $value")
        }
        else {
          println(s"OTHERS: $m")

        }
      }
    }

    loop(topLevelObj, c.tpe)
  }

Some explanation:

I am using an implicit TypeTag instead of a ClassTag, because TypeTag comes with the convenient tpe property, which contains full information about the inspected type. I pass this Type property down to the loop method.