R help - Dec 2009 - Ops method does not dispatch on either of two classes

I have defined boolean methods for bit and bitwhich objects, for example
|.bit <- function(e1,e2)
and
|.bitwhich <- function(e1,e2)

Both methods coerce their arguments to the respective class, however if I do
something like

bit_obj | bitwhich_obj

then I get a warning 

Warning message:
Incompatible methods ("|.bit", "|.bitwhich") for
"|"

and none of the two methods is called. Instead the (internal) method for
logicals seems to be called - not even coercing its arguments to logical. Same
problem with Ops.bit and Ops.bitwhich .

What is the recommended way to get my methods reliably dispatched? 

Jens Oehlschl?gel

This is as documented on the help page for Ops (the page in base, not 
the one in Methods) which is linked from ?"|".  For background you 
should also read the reference on that help page.

You are wrong in asserting that the internal method is 'for logicals': 
please do study the help page.  It covers e.g. integer vectors which 
is what I suspect you have here (assuming this is something to do with 
package 'bit', unmentioned).

On Mon, 28 Dec 2009, Jens Oehlschl?gel wrote:
> I have defined boolean methods for bit and bitwhich objects, for example
> |.bit <- function(e1,e2)
> and
> |.bitwhich <- function(e1,e2)
>
> Both methods coerce their arguments to the respective class, however 
> if I do something like
>
> bit_obj | bitwhich_obj
>
> then I get a warning
>
> Warning message:
> Incompatible methods ("|.bit", "|.bitwhich") for
"|"
>
> and none of the two methods is called. Instead the (internal) method 
> for logicals seems to be called - not even coercing its arguments to 
> logical. Same problem with Ops.bit and Ops.bitwhich .
>
> What is the recommended way to get my methods reliably dispatched?
They are!  Take a look at what classes in R itself have S3 Ops methods 
and how they achieve what you seem to want via class inheritance.
> Jens Oehlschl?gel
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Thanks Brian,
> This is as documented on the help page for Ops (the page in base, not 
> the one in Methods) which is linked from ?"|".  For background
you
> should also read the reference on that help page.
Unfortunately I have no access to that book.
> You are wrong in asserting that the internal method is 'for
logicals':
> please do study the help page.  It covers e.g. integer vectors which 
> is what I suspect you have here (assuming this is something to do with 
> package 'bit', unmentioned).
Yes, both "bit" and "bitwhich" are integer with an S3 class
attribute (bitwhich sometimes is logical instead).

I am lost. What do I need to do to get "|.a" dispatched if calling 
a | b
where "a" and "b" are objects from S3 classes "a"
and "b" that both have methods defined for "|"
?

In the R Language definition I find
"If they do not suggest a single method then the default method is
used."
Does this mean it is not possible to write Ops methods for classes "a"
and "b" such that "|.a" is called in
a | b
?

I don't see how I can get any hook into the dispatch mechanism, my methods
are always bypassed if the classes of e1 and e2 differ (simple example below).
Best wishes for 2010

Jens Oehlschl?gel


> ca <- function(x){
+   x <- as.integer(x)
+   oldClass(x) <- "a"
+   x
+ }
> cb <- function(x){
+   x <- as.integer(x)
+   oldClass(x) <- "b"
+   x
+ }
> 
> a <- ca(1)
> b <- cb(1)
> 
> Ops.a <-
+ function(e1, e2){
+   cat("here Ops.a \n")
+   NULL
+ }
> 
> Ops.b <-
+ function(e1, e2){
+   cat("here Ops.a \n")
+   NULL
+ }
> 
> # OK, "Ops.a" dispatched
> a | a
here |.a 
NULL
> 
> # BUT both, "Ops.a" and "Ops.b" bypassed
> a | b
[1] TRUE
Warning message:
Incompatible methods ("|.a", "|.b") for "|"
> 
> 
> "|.a" <- function(e1, e2){
+ cat("here |.a \n")
+ NULL
+ }
> 
> "|.b" <- function(e1, e2){
+ cat("here |.b \n")
+ NULL
+ }
> 
> # OK, "|.a" dispatched
> a | a
here |.a 
NULL
> 
> # BUT both, "|.a" and "|.b" bypassed
> a | b
[1] TRUE
Warning message:
Incompatible methods ("|.a", "|.b") for "|"