Dynamic object method invocation using reflection in scala

Question

I'm looking to create a way to dynamically call logic depending on template id within scala. So template id 1 calls logic a, template id 2 call logic b, etc. The logic will be diverse but will have the same inputs/outputs. Also the number of different template ids will get into the thousands and will not be known ahead of time, so a loose coupling feels the way to go.

I've started looking at reflection to do this using scala 2.11.1 and can statically use reflection when I know the logic to be used ahead of time but have not found the correct way to dynamically use reflection, so for example passing in template id 2 will call logic b.

Below is a cut down example showing how the static version works and the skeleton I have so far for the dynamic version.

package thePackage

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

trait theTrait { def theMethod(x: String): Unit }

// the different logic held in different objects
object object1 extends theTrait {
  def theMethod(x: String) = { println("a " + x ) }
}

object object2 extends theTrait { 
  def theMethod(x: String) = { println("b " + x ) }
}

object object3 extends theTrait {
  def theMethod(x: String) = { println("c " + x ) }
}

// run static/dynamic reflection methods
object ReflectionTest {

  // "static" invocation calling object1.theMethod
  def staticInvocation() = {
    val m = ru.runtimeMirror(getClass.getClassLoader)
    val im = m.reflect(thePackage.object1)
    val method = ru.typeOf[thePackage.object1.type]
                   .decl(ru.TermName("theMethod")).asMethod
    val methodRun = im.reflectMethod(method)
    methodRun("test")
  }

  staticInvocation

  // "dynamic" invocation using integer to call different methods
  def dynamicInvocation( y: Integer) = {
    val m = ru.runtimeMirror(getClass.getClassLoader)
    val module = m.staticModule("thePackage.object" + y)
    val im = m.reflectModule(module)

    //  stuck... static approach does not work here

  }

  dynamicInvocation(1)
  dynamicInvocation(2)
  dynamicInvocation(3)

}

What needs to be added/changed to the dynamicInvocation method to make this work, or should I be using a different approach?

Iulian Dragos · Accepted Answer · 2014-07-25 10:49:35Z

5

You need to get an instance mirror for your module, on which you can reflect the method.

def dynamicInvocation( y: Integer) = {
  val m = ru.runtimeMirror(getClass.getClassLoader)
  val module = m.staticModule("thePackage.object" + y)
  val im = m.reflectModule(module)
  val method = im.symbol.info.decl(ru.TermName("theMethod")).asMethod

  val objMirror = m.reflect(im.instance)
  objMirror.reflectMethod(method)("test")
}

answered Jul 25, 2014 at 10:49

Iulian Dragos

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Comments

Saurabh Gupte · Accepted Answer · 2016-02-04 18:39:15Z

1

It seems that TermName method in above solution has been replaced by newTermName and also the info.decl seems to not work. Below line worked for me

val method = im.symbol.typeSignature.member(ru.newTermName("testMethod")).asMethod

answered Feb 4, 2016 at 18:39

Saurabh Gupte

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