[Rd] BUG?: A copy of base::`+` (primitive) is not a clone but a "pointer"

[Martin Maechler]

>>>>> Tomas Kalibera 
>>>>>     on Mon, 18 Nov 2019 09:36:14 +0100 writes:

    > On 11/18/19 9:18 AM, Martin Maechler wrote:
    >>>>>>> Henrik Bengtsson
    >>>>>>> on Sun, 17 Nov 2019 14:31:07 -0800 writes:
    >> > $ R --vanilla R version 3.6.1 (2019-07-05) -- "Action of
    >> > the Toes" Copyright (C) 2019 The R Foundation for
    >> > Statistical Computing Platform: x86_64-pc-linux-gnu
    >> > (64-bit) ...
    >> 
    >> >> str(base::`+`)
    >> > function (e1, e2)
    >> 
    >> >> plus <- structure(base::`+`, class = "plus") str(plus)
    >> > function (e1, e2) - attr(*, "class")= chr "plus"
    >> 
    >> > ## Hmm ...
    >> >> str(base::`+`)
    >> > function (e1, e2) - attr(*, "class")= chr "plus"
    >> 
    >> >> class(base::`+`) <- NULL str(base::`+`)
    >> > function (e1, e2)
    >> 
    >> > ## Hmm ...
    >> >> str(plus)
    >> > function (e1, e2)
    >> 
    >> > Even without assigning to `plus`, you get this behavior:
    >> 
    >> > $ R --vanilla
    >> >> structure(base::`+`, class = "plus")
    >> > function (e1, e2) .Primitive("+") attr(,"class") [1]
    >> > "plus"
    >> 
    >> > # Hmm...
    >> >> str(base::`+`)
    >> > function (e1, e2) - attr(*, "class")= chr "plus"
    >> 
    >> > Looks to be the case for common (all?) .Primitive
    >> > functions.
    >> 
    >> No need for 'base::' (who would be crazy enough to redefine `+`?)
    >> nor str() actually:
    >> 
    >> attr(`+`, "class") <- NULL  # (reset)
    >> `+`
    >> structure(`+`, class = "plus")
    >> `+`
    >> 
    >> is clearly convincing and minimal
    >> 
    >>> attr(`+`, "class") <- NULL
    >>> `+`
    >> function (e1, e2)  .Primitive("+")
    >>> structure(`+`, class = "plus")
    >> function (e1, e2)  .Primitive("+")
    >> attr(,"class")
    >> [1] "plus"
    >>> `+`
    >> function (e1, e2)  .Primitive("+")
    >> attr(,"class")
    >> [1] "plus"
    >> ---------------------------------------------------------
    >> 
    >> > Is this expected?
    >> 
    >> no.  (at least not by 99.999% of R users)
    >> 
    >> 
    >> > Should I report this one to Bugzilla?
    >> yes, please.
    >> 
    >> > /Henrik

    > A shorter example is

    >> p1 <- .Primitive('+') ; p2 <- p1 ; attr(p1, "myattr") <- 1 ; p2

    > function (e1, e2)  .Primitive("+")
    > attr(,"myattr")
    > [1] 1

beautiful ; thank you, Tomas !

    > Builtins have referential semantics in R (like e.g. environments, but 
    > also some other types).

    > Tomas

 [aarh.. I knew it ... but am showing my age:  I had forgotten about it.]

I forget (and don't have time just now to find out) where we
have documented it;  it may be good to document also in official
user exposed places such say the  ?.Primitive  help page.

Martin