Getting access to parent model

I'd like to be able to do something like this in a template:

// shows raw text
${my_variable}

// converts to a date type
${my_variable.asDate)

// runs some other arbitrary function on my_variable
${my_variable.asSomethingElse)

I got it to work (partially) by making "my_variable" a class that 
implements both TemplateScalarModel and TemplateHashModelEx. I can get 
both ${my_variable} and ${my_variable.whatever} to return scalars.

Now the tricky part: I need to return the hash values as objects that 
implement TemplateMethodModelEx, and those methods need to get access to 
the text of my_variable.

Unfortunately, Freemarker throws an error when it sees the 
TemplateMethodModelEx ("Expecting a string, date or number here"), and I 
haven't figured out how to get access to the parent model from within my 
method so I can get the text value of "my_variable".

Is what I'm trying to do possible?







I think I could implement the bottom two by making my_variable a 
TemplateHashModel and passing the string value to be converted to it.

The trouble is the top one. FreeMarker throws an exception rather than 
just calling toString() on it. ERROR: Error on line X, column Y in 
/results Expecting a string, date or number here, Expression item is 
instead a com.MyHashModel.OrWhatever.

I'd be happy to do it using ? syntax instead: ${my_variable?asDate}, but 
you can't create your own builtins (according to our exchange on this 
topic Dec 9, 2010).

Is there any way to


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