R devel - Nov 2009 - group generics

I have classes A and B, where B contains A.  In the implementation of
the group generic for B I would like to use the corresponding group
generic for A.  Is there a way to do that?

I would also appreciate any comments if what I'm trying to do seems like
the wrong approach.

Here's a stripped down example:
setClass("A",
         representation=representation(xa="numeric")
         )

setMethod("Arith", signature(e1="numeric",
e2="A"), function(e1, e2) {
  new("A", ax=e1*e2 at xa)
}
          )

setClass("B",
         representation=representation(xb="numeric"),
         contains=c("A")
         )

setMethod("Arith", signature(e1="numeric",
e2="B"), function(e1, e2) {
	# the next line does not work right
  v <- selectMethod("callGeneric", signature=c("numeric",
"A"))(e1, e2)
  print(v)
  new("B", v, xb=e1*e2 at xb)
}
)


Results:
> t1 <- new("B", new("A", xa=4), xb=2)
> t1
An object of class ?B?
Slot "xb":
[1] 2

Slot "xa":
[1] 4
> 3*t1
Error in getGeneric(f, !optional) : 
  no generic function found for "callGeneric"

Thanks.
Ross Boylan

Hi Ross -- 

Ross Boylan <ross at biostat.ucsf.edu> writes:
> I have classes A and B, where B contains A.  In the implementation of
> the group generic for B I would like to use the corresponding group
> generic for A.  Is there a way to do that?
>
> I would also appreciate any comments if what I'm trying to do seems
like
> the wrong approach.
>
> Here's a stripped down example:
> setClass("A",
>          representation=representation(xa="numeric")
>          )
>
> setMethod("Arith", signature(e1="numeric",
e2="A"), function(e1, e2) {
>   new("A", ax=e1*e2 at xa)
typo, I guess, xa = e1...
> }
>           )
>
> setClass("B",
>          representation=representation(xb="numeric"),
>          contains=c("A")
>          )
>
> setMethod("Arith", signature(e1="numeric",
e2="B"), function(e1, e2) {
> 	# the next line does not work right
>   v <- selectMethod("callGeneric",
signature=c("numeric", "A"))(e1, e2)
    v <- callGeneric(e1, as(e2, "A"))

or probably

   v <- callNextMethod(e1, e2)

Martin
>   print(v)
>   new("B", v, xb=e1*e2 at xb)
> }
> )
>
>
> Results:
>> t1 <- new("B", new("A", xa=4), xb=2)
>> t1
> An object of class ?B?
> Slot "xb":
> [1] 2
>
> Slot "xa":
> [1] 4
>
>> 3*t1
> Error in getGeneric(f, !optional) : 
>   no generic function found for "callGeneric"
>
> Thanks.
> Ross Boylan
>
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-- 
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
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