R devel - Jun 2009 - Accessing an object from the function in its .Data slot?

I have an S4 object extending "function". Is it there a good way to
access the object (resp. its slots) from within the function in .Data?

If I'm reading help files correctly, it is not possible to overload
'(' (which would be the most elegant solution, I suppose).  I can
enclose the slotted data in the function when it is created, but that
obviously doesn't work when that data changes later on (also it
duplicates the data).

I tried to use the call stack, and this does seem to work:
> setClass("abcd", representation(.Data="function",
x="character"))
> a = new("abcd",
>     .Data=function() str( get( as.character( sys.call()[[1]] ),
pos=parent.frame() ) ),
>     x="testtxt")
> a()
Formal class 'abcd' [package ".GlobalEnv"] with 2 slots
  ..@ .Data:function (x)
  ..@ x    : chr "testtxt"

That is obviously a not-so-elegant hack, and I'm not sure it works
under all circumstances as I'm not an expert on R's call system.

Is there any better way to achieve this?

Thanks in advance
Martin

Martin Kober wrote:
> I have an S4 object extending "function". Is it there a good way
to
> access the object (resp. its slots) from within the function in .Data?
>   
I don't think so.  That's not really the way the S4 object system is 
designed to work.  If a function needs access to an object, the object 
should be one of the args to the function, or defined in its 
environment.  Where the function happens to be stored is irrelevant.

Duncan Murdoch
> If I'm reading help files correctly, it is not possible to overload
> '(' (which would be the most elegant solution, I suppose).  I can
> enclose the slotted data in the function when it is created, but that
> obviously doesn't work when that data changes later on (also it
> duplicates the data).
>
> I tried to use the call stack, and this does seem to work:
>
>   
>> setClass("abcd", representation(.Data="function",
x="character"))
>> a = new("abcd",
>>     .Data=function() str( get( as.character( sys.call()[[1]] ),
pos=parent.frame() ) ),
>>     x="testtxt")
>> a()
>>     
> Formal class 'abcd' [package ".GlobalEnv"] with 2 slots
>   ..@ .Data:function (x)
>   ..@ x    : chr "testtxt"
>
> That is obviously a not-so-elegant hack, and I'm not sure it works
> under all circumstances as I'm not an expert on R's call system.
>
> Is there any better way to achieve this?
>
> Thanks in advance
> Martin
>
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