any way to get a method handle in scala?

[Ittay Dror]

Hi,

Given:

class Foo {
  def bar(s: String) = ???
}

Is there a way to get a reference to 'bar' in a type safe way, so that I can inspect its argument list and invoke it at runtime?

This is in contrast to `_.bar _` that wraps it in a function object that cannot be inspected (or maybe there is a way with the new reflection?) or using the method name as string with is not type safe.

Regards,
Ittay

[Dennis Haupt]

what do you mean by type safe?

> -------- Original-Nachricht --------
> Datum: Wed, 29 Aug 2012 14:52:44 +0300
> Von: Ittay Dror <ittay...@gmail.com>
> An: scala-user <scala...@googlegroups.com>
> Betreff: [scala-user] any way to get a method handle in scala?

[Ittay Dror]

not getting it by using a string name .

[Dennis Haupt]

is what you want to do a function wrapper with generic type information available at runtime?
should be possible, create your own function wrappers with manifests.

> -------- Original-Nachricht --------
> Datum: Wed, 29 Aug 2012 16:23:30 +0300
> Von: Ittay Dror <ittay...@gmail.com>
> An: Dennis Haupt <h-s...@gmx.de>
> CC: scala...@googlegroups.com
> Betreff: Re: [scala-user] any way to get a method handle in scala?

[Ittay Dror]

There are manifests for methods?

[Dennis Haupt]

i was thinking:

class ManifestFunction1[R:Manifest,T:Manifest](wrapped:Function1[R,T]) {
....
}

val magic = new manifestfunction(method _)

untested, but should work

> -------- Original-Nachricht --------
> Datum: Wed, 29 Aug 2012 17:48:33 +0300

[Daniel Sobral]

Not really. You can approach that somewhat using reflection and
macros, to get a MethodSymbol. You still need to pass a String, but
the macro will make it checked at compile time.

Now, to invoke it you need a method mirror, and a method mirror
requires an instance mirror. All this mirroring is necessary because
to find stuff you need to go through a class loader.

--
Daniel C. Sobral

I travel to the future all the time.

[Flávio W. Brasil]

It's possible to do reflection in a type-safe way using the scala.reflect.Code.

I've been using this trick for a while in a non open source project. I extracted the code to a LGPL project at Github.

It is very based on heuristics and I've not finished to port the unit tests. Probably the framework will be re-written or deprecated with 2.10 reflection.

https://github.com/fwbrasil/sReflection

import net.fwbrasil.sReflection.SReflection._

object Example extends App {

class MyClass {

var string = "a"

def method(s: String) = {

string = s

}

}

val sField = classOf[MyClass].sField(_.string).get

val sMethod = classOf[MyClass].sMethod[String](_.method(_)).get

val obj = new MyClass

require(sField.get(obj) == "a")

sMethod.invoke(obj, "b")

require(sField.get(obj) == "b")

}

-- 

Flávio W. Brasil

fwbrasil.net

[Daniel Sobral]

Mmmmm. I had not thought of having it ask for a function and get the
eta expansion of the method. Workable indeed.