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.
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
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