Skip to content

Instantly share code, notes, and snippets.

@oluies
Forked from gkossakowski/Proxy.scala
Created October 3, 2011 07:08
Show Gist options
  • Save oluies/1258594 to your computer and use it in GitHub Desktop.
Save oluies/1258594 to your computer and use it in GitHub Desktop.
ScalaProxy example
package test;
import java.lang.{reflect => jreflect}
import scala.reflect.mirror._
/**
* Scala counterpart of java.lang.reflect.InvocationHandler
*/
trait InvocationHandler {
def invoke(proxy: AnyRef, method: Symbol, args: Array[AnyRef]): AnyRef
}
object ScalaProxy {
def apply[T <: AnyRef](handler: InvocationHandler)(implicit manifest: Manifest[T]): T = {
val clazz = manifest.erasure
val h = new ScalaHandler(handler)
jreflect.Proxy.newProxyInstance(clazz.getClassLoader(), Array(clazz), h).asInstanceOf[T]
}
private class ScalaHandler(handler: InvocationHandler) extends jreflect.InvocationHandler {
def invoke(proxy: Object, method: jreflect.Method, args: Array[Object]): Object = {
val m = methodToSymbol(method)
handler.invoke(proxy, m, if (args != null) args else Array.empty)
}
/**
* Maps java.lang.reflect.Method to scala.reflect.api.Symbols.Symbol
* corresponding to that method.
*
* TODO: Improved (complete) implementation of this method should
be in Mirror class similarly to classToType method defined there.
*/
private def methodToSymbol(m: jreflect.Method): Symbol = {
val ClassInfoType(_, decls, _) = classToSymbol(m.getDeclaringClass).info
val jname = m.getName
//TODO: handle overloaded defs
decls.find(_.encodedName == jname).get
}
}
}
trait Foo {
def foo(x: Int, y: String): Unit
def bar_!(): Unit
}
/**
* Test of ScalaProxy. Run using trunk version of compiler.
* Type
* scalac Proxy.scala && scala test.Test
*/
object Test extends App {
val h = new InvocationHandler {
def invoke(proxy: AnyRef, m: Symbol, args: Array[AnyRef]): AnyRef = {
//TODO: if method has multiple argument list resultType will be MethodType again
//so we need recursive extraction below
val MethodType(params, resultType) = m.info
val paramsStr = {
val names = params.map(_.name.toString)
val types = params.map(_.info.toString)
((names zip args zip types) map { case ((n, a), t) => n + ": " + t + " = " + a }).mkString("(", ", ", ")")
}
println("called " + m.decodedName + paramsStr + ": " + resultType)
null
}
}
val p = ScalaProxy[Foo](h)
p.foo(1, "str")
p.bar_!()
//prints:
//called foo(x: Int = 1, y: String = str): Unit
//called bar_!(): Unit
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment