[Rd] `slot<-` performs an in-place modification

[Hervé Pagès]

Ah,  looks like this was already reported and discussed here a couple of 
years ago:

https://stat.ethz.ch/pipermail/r-devel/2019-September/078478.html

Had no idea that "core of Bioconductor once took advantage of this 
feature", seems that I've been fooled all these years ;-)

Sounds like this would deserve a big warning in ?`slot<-`

Thanks,

H.


On 22/03/2022 22:17, Hervé Pagès wrote:
> Hi,
>
> I just found out that `slot<-` performs an in-place modification of 
> the object:
>
>   setClass("A", slots=c(stuff="ANY"))
>   x <- new("A", stuff=11:14)
>   y <- `slot<-`(x, "stuff", value=99)
>
> Then:
>
>   y
>   # An object of class "A"
>   # Slot "stuff":
>   # [1] 99
>
>   x
>   # An object of class "A"
>   # Slot "stuff":
>   # [1] 99
>
> That doesn't seem right!
>
> Is this violation of the standard pass-by-value semantic somehow 
> intended here because most of the time people are expected to do 
> 'slot(x, "stuff") <- 99' instead, in which case the violation cannot 
> be observed so does not matter? I didn't find anything in the man page 
> about this.
>
> I see this behavior with R 4.1.3 and current R devel.
>
> Thanks,
>
> H.
>
-- 
Hervé Pagès

Bioconductor Core Team
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