On 10/11/2019 9:17 a.m., Bryan Hanson wrote:
On Nov 10, 2019, at 3:36 AM, Martin Maechler <maech...@stat.math.ethz.ch> wrote:
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)
Thanks for the helpful blog post Martin. Is the following
“test_class” %in% class(some_object)
which I think in your symbols would be
“…” %in% class(x)
safe as far as you see it? By safe, I mean equivalent to your suggestion of
inherits(x, “…”) .
Those aren't equivalent if S4 gets involved. You can see it if you run
this code:
example("new") # Creates an object named t2 of class "trackcurve"
# that contains "track"
inherits(t2, "track") # TRUE
"track" %in% class(t2) # FALSE
I can't think of any examples not involving S4.
Duncan Murdoch
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