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

[Tomas Kalibera]

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

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

Tomas


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