Stavros Macrakis wrote:
On Thu, Jul 30, 2009 at 12:01 PM, Martin Morgan<mtmor...@fhcrc.org> wrote:
S4 objects do not have the semantics of environments, but of lists (or of most
other R objects), so it is as meaningful to ask why identical(s1, s2) returns
TRUE as it is to ask why identical(list(x=1), list(x=1)) returns TRUE.
Thanks for the clarification.
For some reason, I thought that S4 objects (unlike S3 objects) were
objects in the conventional computer science sense, that is, mutable.
S4 objects are mutable in the sense that one can write replacement
methods for them
setClass("A", representation=representation(aValue="logical"))
setGeneric("aValue<-",
function(object, value) standardGeneric("aValue<-"))
setReplaceMethod("aValue", "A", function(object, value) {
slot(object, "aValue") <- value
object
})
> a <- b <- new("A", aValue=FALSE)
> aValue(a) <- TRUE
> a
An object of class "A"
Slot "aValue":
[1] TRUE
while preserving copy-on-change
> b
An object of class "A"
Slot "aValue":
[1] FALSE
Martin
Compare proto objects, which *are* objects in the usual sense:
proto1 <- proto(expr= {x=23})
proto2 <- proto1
proto1$x <- 45
proto2$x
[1] 45 # proto1 and proto2 are the same object
setClass("test",representation(a="logical"))
[1] "test"
s41 <- new("test")
s42 <- s41
s...@a <- TRUE
s...@a # s41 and s42 are different objects
logical(0)
It would thus perhaps be clearer to speak of S4 "values" rather than
S4 "objects".
-s
--
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109
Location: Arnold Building M1 B861
Phone: (206) 667-2793
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