Earlier you wrote > changing "me" to "b1" in A's bB(), allows A to use B's setGeneric() and here mention "intra-class name clashes" (I'm not sure what you mean by this).
In R, classes do not "own" (or contain) generic functions. They can supply methods for generic functions but a generic function is an object that exists outside of any class. C++ and Java do things differently. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf > Of Greg Minshall > Sent: Friday, February 15, 2013 3:35 AM > To: Martin Morgan > Cc: r-help@r-project.org > Subject: Re: [R] 2 setGeneric's, same name, different method signatures > > Martin, > > fantastic. thank you *very* much! that clears lots of things up for > me. > > (for the record: i think that setGeneric overwriting a previous is more > surprising -- thus violating the principle of least surprise -- than one > function overwriting a previous, in that we think of (or, one way to > think of) OOP is that, after finagling to have no clashes on *class* > names, we should not worry about other than intra-class name clashes. > as i said, for the record.) > > thanks again. > > cheers, Greg > ---- > Martin Morgan <mtmor...@fhcrc.org> wrote: > > > > Hi Greg -- > > > > this setGeneric is over-writing the first, as would > > > > f = function() "first" > > f = function() "second" > > f() # "second" > > > > If you'd like to dispatch on a single argument, then > > > > setGeneric("one", function(x, ...) standardGeneric("one")) > > setMethod("one", "A", function(x, ...) "A-method") > > setMetohd("one", "B", function(x, y, ...) "B-method") > > > > The '...' in the generic allow you to add arguments that are 'picked > > off' by methods. The user could provide any value for y, not only an > > object of class "B". > > > > If you'd like to dispatch sometimes on two arguments then > > > > setGeneric("two", function(x, y, ...) standardGeneric("two")) > > setMethod("two", c("A", "ANY"), function(x, y, ...) "A,ANY-method") > > setMethod("two", c("B", "B"), function(x, y, ...) "B,B-method") > > > > then two(new("A")), two(new("A"), new("A")) and two(new("A"), > > new("B")) end up in A,ANY,two-method while two(new("B"), new("B")) > > ends up in "B,B,two-method". Other combinations are errors. One might > > instead not define A,ANY but instead > > > > setMethod("two", c("A", "missing"), function(x, y, ...) "A,missing-method") > > > > and then two(new("A"), new("A")) would be an error. > > > > Multiple dispatch is complicated, and perhaps best to avoid if possible. > > > > It's possible to write a generic and methods that dispatch on '...', > > with the requirement that all classes are the same; this in the spirit > > of comparing two B's and returning the smaller; see ?dotsMethods > > though again this is not a trivial use case. > > > > Hope that helps enough. > > > > Martin > > ______________________________________________ > R-help@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. ______________________________________________ R-help@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.
