[Rd] [R] assign / environment side effect on R 2.4.0

[Peter Dalgaard]

"Gabor Grothendieck" <ggrothendieck at gmail.com> writes:

> I have moved this discussion to r-devel.
> 
> The example of the poster suggests that the functionality as implemented
> so far in the upcoming 2.4.0 is at this point not correct and needs to
> be fixed prior to release.
> 
> It violates the idea in R that if one modifies a list in a function then a copy
> of that list gets created (at least conceptually) for use within a function
> (rather than the original list being modified) and effectively turns what would
> have been a local variable into an error-prone global variable.
> 
> 
> On 6/26/06, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
> > Please do study the posting guide, as there is no `R 2.4.0'.
> >
> > This seems to be related to the NEWS item
> >
> >     o  [[ on a list does not duplicate the extracted element unless
> >        necessary.  (It did not duplicate in other cases, e.g. a
> >        pairlist.)
> >
> > Now in so far as I can follow it, in your example [[ behaves in the same
> > way as $ always did (which is what informed people would expect).

Well, informed people would expect $ and [[ to behave the same, but
they would _not_ expect

> e1 <- environment(L$test)
> solver(L)
> e2 <- environment(L$test)
> print(e1)
<environment: R_GlobalEnv>
> print(e2)
<environment: 0x12f23a8>

unless perhaps substitute() or similar magic was invoked inside
solver() to create call-by-reference semantics. What we have is an
assignment to "test" in the evaluation frame of solver(), which is a
shallow copy of a shallow copy of L$test, so NAMED should be 2 and
modification should force duplication.

In R-devel, this happens with both [[ and $, and in earlier versions
apparently only with $, which seems to be a case where fixing one bug
unmasks another - i.e. $ was always wrong, now both are.

As far as I can see, either assign() or environment<-() has the bug. 

> > R-help is not the place to discuss unreleased versions of R, nor for
> > questions about code development.  (Did I mention studying the posting
> > guide?)
> >
> >
> > On Fri, 23 Jun 2006, Thomas Petzoldt wrote:
> >
> > > Sorry,
> > >
> > > the posted example had the side effect on all platforms (correctly: R
> > > 2.2.1/Windows, 2.3.1/Linux, 2.4.0/Windows), but in the following
> > > corrected example the behavior of 2.4.0 differs from the older versions.
> > >
> > > The only difference between the "wrong" and the "new" example is
> > > L[["test"]] vs. L$test in the assign.
> > >
> > > Thomas P.
> > >
> > >
> > > envfun <- function(L) {
> > > #  L <- as.list(unlist(L))
> > >  p <- parent.frame()
> > >  assign("test", L[["test"]], p) ## [["test"]] instead of $test
> > >  environment(p[["test"]]) <- p
> > > }
> > >
> > >
> > > solver <- function(L) {
> > >  envfun(L)
> > >  # some other stuff
> > > }
> > >
> > > L <- list(test = function() 1 + 2)
> > >
> > > e1 <- environment(L$test)
> > > solver(L)
> > > e2 <- environment(L$test)
> > >
> > > print(e1)
> > > print(e2)
> > >
> > > ______________________________________________
> > > R-help at stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> > >
> >
> > --
> > Brian D. Ripley,                  ripley at stats.ox.ac.uk
> > Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> > University of Oxford,             Tel:  +44 1865 272861 (self)
> > 1 South Parks Road,                     +44 1865 272866 (PA)
> > Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> >
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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