[R-pkg-devel] slightly polemic question re R CMD check

[David Hugh-Jones]

Hi Jeff,

I wouldn't say R encourages that in general. Non-generic functions will
throw an error if you use a non-existent argument. And some generic
functions check for it:

seq(1, 3, blah = 1)
[1] 1 2 3
Warning message:
In seq.default(1, 3, blah = 1) :
 extra argument ‘blah’ will be disregarded

In fact there is even a `chkDots()` function to help with this - which,
despite having used R or 17 years, I first discovered today :-). So, it
seems the R base developers thought lenient argument checking could be a
bad thing, presumably because it lets errors go undetected.

Maybe chkDots is a reasonable workaround. But I wonder what the rationale
is for R CMD check enforcing that methods *must* be as lenient as the
generic. It seems to lead to a lot of documentation of the form:

@param ... Not used.

Cheers,
David


On Sun, 8 Mar 2020 at 16:24, Jeff Newmiller <jdnewmil using dcn.davis.ca.us>
wrote:

> You seem to think this is a bad thing. R does encourage lenient argument
> checking... what rock have you been under for the last 20 years?
>
> On March 8, 2020 5:41:51 AM PDT, David Hugh-Jones <
> davidhughjones using gmail.com> wrote:
> >You're quite right :-) But I think the polemic still holds, because I
> >have
> >to add manual argument checking to all my methods, which has a cost in
> >lines of code. Indeed, few base R methods have chosen to do this. In
> >effect, the current setup encourages writing methods with "lenient"
> >argument specifications.
> >
> >Thank you for the suggestion about ellipsis.
> >
> >On Sun, 8 Mar 2020, 11:04 Gábor Csárdi, <csardi.gabor using gmail.com> wrote:
> >
> >> You can add the ... argument to chop.default(), and then check that
> >> length(list(...)) is zero.
> >>
> >> Also, you might be interested in the ellipsis package.
> >>
> >> Gabor
> >>
> >> On Sun, Mar 8, 2020 at 10:56 AM David Hugh-Jones
> >> <davidhughjones using gmail.com> wrote:
> >> >
> >> > Hi all,
> >> >
> >> > My package defines the following method and generic:
> >> >
> >> > chop <- function (x, ...) UseMethod("chop")
> >> >
> >> > chop.default <- function (x, breaks, labels, extend = NULL, drop =
> >TRUE)
> >> {
> >> > ... }
> >> >
> >> > R CMD check then gives a warning:
> >> >
> >> > W  checking S3 generic/method consistency (695ms)
> >> >    chop:
> >> >      function(x, ...)
> >> >    chop.default:
> >> >      function(x, breaks, labels, extend, drop)
> >> >
> >> >    See section ‘Generic functions and methods’ in the ‘Writing R
> >> >    Extensions’ manual.
> >> >
> >> > I can fix this by adding a ... argument to chop.default:
> >> >
> >> > chop.default <- function (x, breaks, labels, extend = NULL, drop =
> >> > TRUE, ...)
> >> >
> >> > But that makes the code less robust because e.g.
> >> >
> >> > chop(x, Breaks = 1:3)
> >> >
> >> > will no longer throw an error from the misspelled argument.
> >> >
> >> > Or I can write:
> >> >
> >> > chop(x, breaks, labels, extend, drop) UseMethod("chop")
> >> >
> >> > but this means I cannot use a different interface for a different
> >method.
> >> >
> >> > This seems like a mistake. (That's the polemic.) Or am I missing a
> >better
> >> > way? (That's the question.)
> >> >
> >> > David
> >> >
> >> >         [[alternative HTML version deleted]]
> >> >
> >> > ______________________________________________
> >> > R-package-devel using r-project.org mailing list
> >> > https://stat.ethz.ch/mailman/listinfo/r-package-devel
> >>
> >
> >       [[alternative HTML version deleted]]
> >
> >______________________________________________
> >R-package-devel using r-project.org mailing list
> >https://stat.ethz.ch/mailman/listinfo/r-package-devel
>
> --
> Sent from my phone. Please excuse my brevity.
>

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