group generics

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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?

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

A different error this time, one that looks a lot like the report from
Stephen.Pope at ubs.com on 2007-12-24 concerning callNextMethod:, except
this is with
callGeneric.

HOWEVER, the problem is erratic; when I started from scratch and took
this code into a workspace and executed the commands, they worked as
expected.  I had various false starts and revisions, as well as the real
code on which the example is based, when the error occurred.  I tried
taking in the real code (which defines generics with Arith from my
actual classes, and which also fails as below), and the example still
worked.


My revised code:

setClass("A",
         representation=representation(xa="numeric")
         )

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

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

setMethod("Arith", signature(e1="numeric", e2="B"), function(e1, e2) {
  new("B", xb=e1*e2 at xb, callNextMethod())
}
)

Results:

options(error=recover)
tb <- new("B", xb=1:3, new("A", xa=10))
3*tb

Error in get(fname, envir = envir) : object '.nextMethod' not found

Enter a frame number, or 0 to exit

 1: 3 * tb
 2: 3 * tb
 3: test.R#16: new("B", xb = e1 * e2 at xb, callNextMethod())
 4: initialize(value, ...)
 5: initialize(value, ...)
 6: callNextMethod()
 7: .nextMethod(e1 = e1, e2 = e2)
 8: test.R#6: new("A", xa = callGeneric(e1, e2 at xa))
 9: initialize(value, ...)
10: initialize(value, ...)
11: callGeneric(e1, e2 at xa)
12: get(fname, envir = envir)

Selection: 0

The callGeneric in frame 11 is trying to get the primitive for
multiplying numeric times numeric.  Quoting from Pope's analysis:
[The primitive...]

does not get the various "magic" variables such as .Generic, .Method,
etc. defined in its frame. Thus, callGeneric() fails when, failing to
find ".Generic" then takes the function symbol for the call (which
callNextMethod() has constructed to be ".nextMethod") and attempts to
look it up, which of course also fails, leading to the resulting error
seen above.

I'm baffled, and hoping someone on the list has an idea.
I'm running R 2.10 under ESS (in particular, I use c-c c-l in the code
file to read in the code) on XP.
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