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

[Jeff Newmiller]

R encourages the use of ... particularly in S3 generics, to avoid over-depending on inheritance to enable flexible use of these generics. That is, when you call the generic without knowing which class you are giving it, you cannot specify class-specific arguments. However, some methods have obvious alternative class-specific behaviors that are typically enabled using class-specific arguments (e.g. plot). You cannot support both fully-generic calls and class-specific calls without giving the generic some flexibility that won't get used in some cases.


On March 8, 2020 9:41:51 AM PDT, David Hugh-Jones <davidhughjones using gmail.com> wrote:
>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]]
>> >
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>>
>> --
>> Sent from my phone. Please excuse my brevity.
>>

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