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!
______________________________________________
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.
--
Computational Biology
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109
Location: M1-B861
Telephone: 206 667-2793
______________________________________________
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.
