Creating ColdFusion Proxy Components With ColdFusion 9's GetFunctionCalledName()

Two comments.

1) You could change this,

<cfset this.getValue = variables.proxyMethod />
<cfset this.getVoid = variables.proxyMethod />
<cfset this.getComponent = variables.proxyMethod />

possibly to a call that gets the metadata on variables.target. You could then loop over the functions and dynamically set your pointers. That way if you add X to Test() you won't have to update Proxy.

2) Any reason though why you just don't use onMissingMethod?

@Ben,

Ok, makes sense to me.

That is neat/cool. Currently can't figure a use for it, but I'm sure I will.

I was chatting about testing for equality between cfc's recently and have written up a few notes.

I like the simplicity of dropping in a uuid as an instance identifier, but thought i'd share how it can be done with java

http://chris.m0nk3y.net/blog/post/testing-for-equality-in-coldfusion

You can test for pointer reference equality not directly though. I only have Railo installed on my Machine so I can't definitively say it will work across the board but both ColdFusion and Railo arrays extend the Java.util.Vector class as far as I am aware which is the key to the solution. The solution is to use the Java contains method available on the Collection type objects. In Railo 3.1.2.001 the following works:

<cfset myObject1 = CreateObject( "component", "Test" )/>
<cfset myObject2 = CreateObject( "component", "Test" )/>
<cfset myObject3 = myObject1/>
 
<cfset arr = [myObject1]/>
<!--- The following dumps: true --->
<cfdump var="#arr.contains(myObject1)#"/>
<!--- The following dumps: false--->
<cfdump var="#arr.contains(myObject2)#"/>
<!--- The following dumps: true --->
<cfdump var="#arr.contains(myObject3)#"/>

Perhaps this will be useful to some. Certainly made my life easier with what I was doing...

As a follow up to my comment my "solution" does not work in CF8... all the above cases result in the dump being true. Perhaps ColdFusion trying to be too clever? I'm glad I tried it in Railo first though.

@Chris,

Here's how to test for CFC reference equality using the underlying Java layer in CF9 without writing a Java class to handle it:

component
{
	_internalObj = getPageContent().getPage();
	// get the CFC's compiled page class instance;
	// we can call its underlying Java methods
 
	/**
	* Proxy for the internal object's equals method.
	* CF9 does not allow us to name a method 'equals'
	* as it is a reserved keyword.
	* It's honestly pretty silly, because you can
	* assign the isEqualTo method to this.equals later.
	**/
	function isEqualTo(obj)
	{
	return obj.equals(_internalObj);
	}
	isEqualTo.getMetadata().name = "equals";
	// getMetadata is a method on the UDFMethod Java class,
	// but you could call getMetadata(isEqualTo)
	// and it'd be the same.
	this.equals = isEqualTo;
	structDelete(this, "isEqualTo");
	// reassigning it to the name "equals" is actually
	// an important part of making this work
	// as you'll see below.
}

That's all there is to it.

You might look at this and think "won't that cause an infinite loop?" Well here are the steps that are taken when you call objA.equals(objB):

1. objA passes its _internalObj variable to objB's equals method.

2. objB calls objA's _internalObj equals method and passes its own _internalObj to that method, returning the result.

As you can see, with the isEqualTo method being renamed to "equals" it allows us to bounce the function execution between the two variables' methods in order to reach a scenario where we are essentially calling objA._internalObj.equals(objB_internalObj), resulting in a correct reference equality comparison between the two variables without actually exposing their internal objects (the compiled CFComponent Java class) outside the CFC itself.

Actually looking at my code and my comment about not "exposing their internal objects ... outside the CFC itself." is incorrect, as an object passed to the equals method could have its own equals method written to intercept the internal object passed to it. The following change closes that hole:

	function isEqualTo(obj)
	{
		// if equals is null, then we're at the Java object OR if it's not null then we can check the hashCode equality to see if it's THIS method and not some imposter method or a Java object's field.
		if (isNull(obj.equals) || this.equals.hashCode() == obj.equals.hashCode())
			return obj.equals(_internalObj);
		else
			// if we reach this point then the object references will never be equal.
			return false;
	}
	isEqualTo.getMetadata().name = "equals";
	this.equals = variables.isEqualTo;
	structDelete(this, "isEqualTo");

And finally, doing some more investigating, replacing the entire body of the isEqualTo method with

return objectEquals(this, obj);

works exactly the same.

As for pointer reference equality, I know that MXUnit uses the java.lang.System.identityHashcode() method for its implementation of assertSame(). It seems to be working perfectly across different platforms.

Ehm, actually it is identityHashCode(). That matters, since Java is obviously case sensitive.

http://download.oracle.com/javase/1.4.2/docs/api/java/lang/System.html#identityHashCode(java.lang.Object)

@Ben, @Graeme

Building a simple proxy at the moment, and though don't fully understand all that is going on I have it working.

so if I understand things correctly would

return objectEquals(this, obj);

replace the UUID check you do?

@Ray

I've only use onMissingMethod a couple of times. In this proxy how would I implement.

thanks

@Kevin,

Having dug into ColdFusion's Java bytecode; the simplest way I can explain it is that objectEquals(obj1, obj2) invokes the java.lang.Object.equals(obj) method on obj1 and is given obj2 as its parameter. (It does a little bit more than that but those details aren't pertinent here.)

So essentially any time you want to verify whether two different ColdFusion variables are referencing the exact same object, objectEquals will be able to give you the answer to that. So yes, if you're using UUIDs to track object identity so you can use it to compare whether two variables reference the same object, you can replace it with objectEquals.

I just found this post and was wondering (please don't laugh too hard if it's a dumb question), can this technique be used to proxy web services as well?

wow great work