CFML: getObjectMetadata()

G'day:
This is a strange article, this one. It started off just being a feature request which I was typing into the Adobe bug tracker, but decided to write my thoughts up here, by way of soliciting other people's thoughts too. On re-read just before pressing "publish", I realise the framing for the point is about five times longer than the point itself. Oops. Oh well. It's a slow news day here. It's Monday after all.

ColdFusion has a function getMetadata(),  which can be called on a variety of objects: an CFC instance, a user-defined function, a property, a query. I'm just focusing on on its usage with "objects".

Here's an example of getMetadata() being called on an object:

// Bloggable.cfc
interface {

    public void function g(required numeric x);

}

// Parent.cfc
/**
@hint Parent component
*/
component {

    /**
    * @hint Method defined in Parent
    */
    public void function g(required numeric x){
        return;
    }

}

// Sub.cfc
/**
@hint Demonstrating getMetadata() results
*/
component extends="Parent" implements="Bloggable" {

    /**
    * @hint Method defined in Sub
    * @x A number
    */
    public void function f(required numeric x){
        return;
    }

}

<!--- test.cfm --->
<cfdump var="#getMetadata(new Sub())#">

Output:

struct
EXTENDS	struct EXTENDS struct FULLNAME WEB-INF.cftags.component NAME WEB-INF.cftags.component PATH C:\Apps\JRunservers\www.scribble.local\ cfusion.ear\cfusion.war\WEB-INF\cftags\component.cfc TYPE component FULLNAME cf.cfml.functions.system.getMetadata.blog.Parent FUNCTIONS array 1 struct ACCESS public HINT Method defined in Parent NAME g PARAMETERS array 1 struct NAME x REQUIRED true TYPE numeric RETURNTYPE void HINT Parent component NAME cf.cfml.functions.system.getMetadata.blog.Parent PATH D:\websites\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\Parent.cfc TYPE component
FULLNAME	cf.cfml.functions.system.getMetadata.blog.Sub
FUNCTIONS	array 1 struct ACCESS public HINT Method defined in Sub NAME f PARAMETERS array 1 struct HINT A number NAME x REQUIRED true TYPE numeric RETURNTYPE void
HINT	Demonstrating getMetadata() results
IMPLEMENTS	struct Bloggable struct EXTENDS struct WEB-INF.cftags.interface struct FULLNAME WEB-INF.cftags.interface NAME WEB-INF.cftags.interface PATH C:\Apps\JRunservers\www.scribble.local\ cfusion.ear\cfusion.war\WEB-INF\cftags\interface.cfc TYPE interface FULLNAME cf.cfml.functions.system.getMetadata.blog.Bloggable FUNCTIONS array 1 struct ACCESS public NAME g PARAMETERS array 1 struct NAME x REQUIRED true TYPE numeric RETURNTYPE void NAME cf.cfml.functions.system.getMetadata.blog.Bloggable PATH D:\websites\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\Bloggable.cfc TYPE interface
NAME	cf.cfml.functions.system.getMetadata.blog.Sub
PATH	D:\websites\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\Sub.cfc
TYPE	component

Lovely: everything we'd want to know about that object.

Despite being called on an object, getMetadata() returns the metadata for the CFC, not the actual object. Changes made to the object after it's been instantiated are not reflected in the returned metadata, eg:

<!--- test.cfm --->
<cfscript>
    o = new Sub();

    function h(){
        writeOutput("Hi!");
    }
    o.h = h;    // stick it in the object
    o.h(); // prove it works

    writeDump(getMetadata(o));    // but where is it?
</cfscript>

Output:

Hi!

struct
EXTENDS
FULLNAME	cf.cfml.functions.system.getMetadata.blog.Sub
FUNCTIONS	array 1 struct ACCESS public HINT Method defined in Sub NAME f PARAMETERS array 1 struct HINT A number NAME x REQUIRED true TYPE numeric RETURNTYPE void
HINT	Demonstrating getMetadata() results
IMPLEMENTS
NAME	cf.cfml.functions.system.getMetadata.blog.Sub
PATH	D:\websites\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\Sub.cfc
TYPE	component

(I've collapsed a bit of it so as to minimise repetitive clutter).

This - to me - is a bug: we've got a function getComponentMetadata(), and that should be getting the metadata for a component. getMetadata(), when having an object passed to it, should get metadata on that object. Not on the object's underlying component. Anyway, I've already dwelt on that and I have nothing new to add.

What would work around this bug would be to have a getObjectMetadata(), which simply does what it claims it does: gets the metadata of the actual object passed to it, rather than the CFC it was an instance of.

That in itself is not so interesting, but I'd also envisage the metadata to be writable. For example, if I push another function into the metadata, this is reflected in the object. We can already push functions into objects - as demonstrated above - but there's other stuff we can't do. How about pushing functions into the object so that it fulfills an interface contract, and then also setting the object's implements metadata to tell it it now implements that interface; so it can then be used in situations in which we need that interface. Or - and god knows the ramifications of this - changing the extends metadata of the object so it extends some different parent component?

TBH, the most useful thing would be for it to return the metadata of the actual object, not the component the object is an instance of. But I've had situations in which being able to make an existing object fulfill an interface contract would have been useful. But then again I bring this upon  myself because I use interfaces. Maybe I just shouldn't.

Anyway, any thoughts on this sort of thing? I've raised it as E/R 3594771.

---

Update:
Ooh. I forgot... what does Railo do about all this? Well Railo does actually include some metadata for the injected function, h():

functions

Array 1 Struct access string public closure boolean false description string hint string Method defined in Sub name string f output boolean true owner string C:\Apps\railo-express-jre-win64\webapps\railo\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\Sub.cfc parameters Array 1 Struct hint string A number name string x required boolean true type string numeric returnFormat string wddx returntype string void 2 Public Function h source:C:\Apps\railo-express-jre-win64\webapps\railo\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\test2.cfm arguments label name required type default hint return type any

Although it's clearly not being considered in quite the same way that the compile-time-present functions are. The metadata here is a bit sparse (and not correct, either). For the purposes of this example, I changed h() to be:

public void function h() hint="Hi!"{
    writeOutput("Hi!");
}

So in that dump, Railo is omitting the hint, and reporting the returntype incorrectly. If I dump output on the function itself, rather than the object, I get a more pleasing (if not aesthetically) result:

Struct
access	string public
closure	boolean false
description	string
hint	string Hi!
name	string h
output	boolean true
owner	string C:\Apps\railo-express-jre-win64\webapps\railo\www.scribble.local\cf\cfml\functions\system\getMetadata\blog\test.cfm
parameters	Array
returnFormat	string wddx
returntype	string void

So this is something. Good ole Railo.


--
Adam