[Rd] structure(<primitive function>, ...) is sticky: a bug, or should it be an error?

[Martin Maechler]

>>>>> Henrik Bengtsson 
>>>>>     on Thu, 20 Mar 2025 11:55:05 -0700 writes:

    >> 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

In such cases, I always go to  https://developer.r-project.org/
and look at the release schedule.

Important for this Q seems

* Friday 2025-03-14: GRAND-FEATURE FREEZE (4.5.0 alpha)
* Friday 2025-03-28: FEATURE FREEZE (4.5.0 beta)
* Friday 2025-04-04: CODE FREEZE (4.5.0 RC) 

So, yes there's a possibility  ... but as you mentioned, too,
it depends quite a bit on if the fix is easily affectiong useR
and CRAN/Bioc package space.

Martin

    > On Thu, Mar 20, 2025 at 3:31 AM Martin Maechler
    > <maechler using 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