> I'm pretty convinced we should fix it by checking for primitive
> functions inside the C code of `attributes<-` :
> arguably the bug is really there, rather than in structure().
>
> Patches are welcome (via R's Bugzilla or just here).
Thank you Martin. I'll make sure I create a brief BugZilla report on
this, and hopefully a follow with a patch later on.
One question on urgency or not: Is it too late to get such a change in
for the R 4.5.0 release? I suspect so, because it has a potential of
breaking existing packages. But if there's a possibility of fixing
this in R 4.5.0, I'll make this a top priority. Please let me know.
/Henrik
On Thu, Mar 20, 2025 at 3:31 AM Martin Maechler
<maech...@stat.math.ethz.ch> wrote:
>
> >>>>> Henrik Bengtsson
> >>>>> on Wed, 19 Mar 2025 10:58:46 -0700 writes:
>
> > Hello.
> > I just (re-)discovered that structure(sum, init = 100) is "sticky",
> > i.e. it stays with base::sum(). Here's an minimal example:
>
> > $ R --vanilla --quiet
> >> void <- structure(sum, some_attr = TRUE)
> >> str(sum)
> > function (..., na.rm = FALSE)
> > - attr(*, "some_attr")= logi TRUE
>
> >> From my very basic troubleshooting, it looks like this is happening
> > for primitive functions. I think I understand that this comes down to
> > primitive functions cannot be copied and baseenv() being special, i.e.
> > in structure() there will be no copy made of the primitive function,
> > and then attributes()<- ends up modifying the original primitive
> > function. Even if this is a documented feature, I believe, it is a
> > silent feature with risky side effects. We might already have code out
> > there that silently produces incorrect results, because of this
> > behavior. For example, I was about to a custom reduce() function where
> > I control the initial value via an "init" attribute of the reducer
> > function, e.g.
>
> > x <- 1:10
> > sum1 <- reduce(x, `+`)
> > sum2 <- reduce(x, structure(`+`, init = 100)) # == 100 + sum1
>
> > If I then call:
>
> > sum3 <- reduce(x, `+`)
>
> > the 'init' attribute that was set in the sum2 statement will affect
> > sum3 such that sum3 == sum2, not sum3 == sum1 as one would expect.
>
>
> > SUGGESTIONS:
>
> > If this is a bug, then I think it needs to be fixed. If it cannot be
> > fixed, maybe this could be protected against, e.g.
>
> >> void <- structure(sum, some_attr = TRUE)
> > Error: You must not set attributes on a primitive function: sum
>
> > Maybe it's sufficient to implement a protection against this in
> > attr()<-, attributes()<-, and class()<-.
>
> > Comments?
>
> > /Henrik
>
> Yes, this is a bug -- a version of your code above:
>
> > void <- structure(sum, foo = TRUE)
> > identical(void, sum)
> [1] TRUE
> > sum
> function (..., na.rm = FALSE) .Primitive("sum")
> attr(,"foo")
> [1] TRUE
> >
>
> Above, you are already looking at ways to deal with it; and that
> *is* more delicate, indeed:
>
> One thing we (R core) found previously (a couple of years ago)
> was that the `structure(..)` function was
> already too "slow" for it to be used in some base R functions,
> and adding another if(..) to it will not help making it faster ...
>
> OTOH, structure() being a pure R function (no direct .Internal(), .Call() ..)
> is also important I think, as it keeps its code nicely self documenting.
>
> I'm pretty convinced we should fix it by checking for primitive
> functions inside the C code of `attributes<-` :
> arguably the bug is really there, rather than in structure().
>
> Patches are welcome (via R's Bugzilla or just here).
>
> Martin
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
