>>>>> Gabriel Becker
>>>>> on Sat, 2 Nov 2019 12:37:08 -0700 writes:
> I agree that we can be careful and narrow and still see a
> nice improvement in behavior. While Herve's point is valid
> and I understand his frustration, I think staying within
> the matrix vs c(matrix, array) space is the right scope
> for this work in terms of fiddling with inheritance.
[.................]
> > Also, we seem to have a rule that inherits(x, c) iff c %in% class(x),
>
> good point, and that's why my usage of inherits(.,.) was not
> quite to the point. [OTOH, it was to the point, as indeed from
> the ?class / ?inherits docu, S3 method dispatch and inherits
> must be consistent ]
>
> > which would break -- unless we change class(x) to return the whole
> set of inherited classes, which I sense that we'd rather not do....
[................]
> Note again that both "matrix" and "array" are special [see ?class] as
> being of __implicit class__ and I am considering that this
> implicit class behavior for these two should be slightly
> changed ....
>
> And indeed I think you are right on spot and this would mean
> that indeed the implicit class
> "matrix" should rather become c("matrix", "array").
I've made up my mind (and not been contradicted by my fellow R
corers) to try go there for R 4.0.0 next April.
I've found the few places in base R that needed a change (to
pass 'make check-all' in the R sources) and found that indeed a
overzealous check in 'Matrix' needed also a change (a place
where the checking code assume class(<matrix>) |--> "matrix" ).
There are certainly many more package (codes and checks) that
need adaption .. i.e., should be changed rather *before* the
above change is activated in R-devel (and then will affect all CRAN
and Bioconductor checks.)
To this end, I've published an 'R Blog' yesterday,
http://bit.ly/R_blog_class_think_2x
which translates to
https://developer.r-project.org/Blog/public/2019/11/09/when-you-think-class.-think-again/index.html
notably mentioning why using class(x) == "...." (or '!=') or
switch(class(.) ...) is quite unsafe and hence bad and you
should very often not replace class(x) by class(x)[1] but
really use the "only truly correct" ;-)
inherits(x, "...")
or
is(x, "....") # if you're advanced/brave enough (:-) to
# use formal classes (S4)
Martin Maechler
ETH Zurich and R Core Team
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