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

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 at 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 at 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 G?bor Cs?rdi, <csardi.gabor at 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 at 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

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--
Sent from my phone. Please excuse my brevity.