Assignment to a slot in an S4 object in a list seems to violate copy rules?

On Thu, Sep 30, 2010 at 8:15 AM, peter dalgaard <pdalgd at gmail.com> wrote:

On Sep 30, 2010, at 16:19 , Niels Richard Hansen wrote:

setClass("A", representation(a = "numeric"))
B <- list()
myA <- new("A", a = 1)
B$otherA <- myA
B$otherA at a <- 2
myA at a

R version 2.12.0 Under development (unstable) (2010-09-13 r52905)
Platform: i386-apple-darwin9.8.0/i386 (32-bit)

--- not anymore, it seems: ---

setClass("A", representation(a = "numeric"))

[1] "A"

B <- list()
myA <- new("A", a = 1)
B$otherA <- myA
B$otherA at a <- 2
myA at a

[1] 1

sessionInfo()

R version 2.12.0 alpha (2010-09-29 r53067)
Platform: x86_64-apple-darwin10.4.0 (64-bit)

So somewhere in the last 162 commits, this got caught. Probably r52914, but it looks like it hasn't been recored in NEWS (and it should be as this was apparently a live bug, not an obscure corner case):

r52914 | luke | 2010-09-15 19:06:13 +0200 (Wed, 15 Sep 2010) | 4 lines

Modified applydefine to duplicate if necessary to ensure that the
assignment target in calls to assignment functions via the complex
assignment mechanism always has NAMED == 1.

Yes, that was the one.  It was reported as a bug back then too, and
there was quite a bit of discussion that ended up with Luke's fix.

     -thomas

-- 
Thomas Lumley
Professor of Biostatistics
University of Washington, Seattle