Thanks Martin. What i'm hoping to do is have a class object, with a member method that can change values of slots in the object, without having to assign values by external assignment to the object. Something like this: setClass ( "Element", representation ( x = "numeric", y = "numeric" ),
prototype = list( x = 0, y = 1 ) ) setGeneric( name = "ComputeX", def = function( self ) standardGeneric("ComputeX") ) setMethod( "ComputeX", signature = "Element", function ( self ) { if ( self @ y > 0 ) { self @ x = pi } } ) so that a call to the method ComputeX assigns ('internally') a value to the slot x of the global object. One can do : a = new( 'Element' ) a @ x = 2 but i would prefer to have a class method do the work without having to explicitly call a @ x = 2. Having to do this means that i need code in my main processing app that does things on slots that normally i would do in a class method. As I understand it, Reference Classes provide this. So i'm naturally wondering if i should switch my app from S4 to RC. Fundamentally, I don't clearly understand S4 and what the difference is between creating a SetReplaceMethod vs a SetMethod, since it seems that in either case one has to 'externally' assign the slot value. My limitation, of course. On 9/14/2011 12:17 AM, Martin Morgan wrote: On 09/13/2011 10:54 AM, Joseph Park wrote: Hi, I'm looking for some guidance on whether to use S4 or Reference Classes for an analysis application I'm developing. I'm a C++/Python developer, and like to 'think' in OOD. I started my app with S4, thinking that was the best set of OO features in R. However, it appears that one needs Reference Classes to allow object methods to assign values (other than the .Object in the initialize method) to slots of the object. With setClass("A", representation=representation(slt="numeric")) a slot can be updated with @<- and an object updated with a replacement method setGeneric("slt<-", function(x, ..., value) standardGeneric("slt<-")) setReplaceMethod("slt", c("A", "numeric"), function(x, ..., value) { x@slt <- value x }) so > a = new("A", slt=1) > slt(a) = 2 > a An object of class "A" Slot "slt": [1] 2 The default initialize method also works as a copy constructor with validity check, e.g., allowing multiple slot updates setReplaceMethod("slt", c("A", "ANY"), function(x, ..., value) { initialize(x, slt=as.numeric(value)) }) > slt(a) = "1" This is typically what I prefer: creating an object, then operating on the object (reference) calling object methods to access/modify slots. So I'm wondering what (dis)advantages there are in developing with S4 vs Reference Classes. R's copy-on-change semantics leads me to expect that b = a slt(a) = 2 leaves b unchanged, which S4 does (necessarily copying and thus with a time and memory performance cost). A reference class might be appropriate when the entity referred to exists in a single copy, as e.g., an on-disk data base, or an external pointer to a C++ class. Martin Things of interest: Performance (i.e. memory management) Integration compatibility with R packages ??? other issues Thanks! ______________________________________________ [1]R-help@r-project.org mailing list [2]https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide [3]http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. References 1. mailto:R-help@r-project.org 2. https://stat.ethz.ch/mailman/listinfo/r-help 3. http://www.R-project.org/posting-guide.html ______________________________________________ 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.