[Rd] Allowing S3 methods of rounding functions to take `...`

[Abby Spurdle]

That's a great suggestion Davis.

While, we're on the topic...
Could we have a "dots" argument in base::t, the transpose function?


On Fri, Jan 29, 2021 at 4:48 AM Davis Vaughan <davis using rstudio.com> wrote:
>
> I should also say that I would be willing to attempt a patch for this, if
> others agree that this would be useful.
>
> - Davis
>
> On Thu, Jan 28, 2021 at 9:14 AM Davis Vaughan <davis using rstudio.com> wrote:
>
> > Hi all,
> >
> > I would like to propose adding `...` to the signatures of the following
> > rounding functions:
> >
> > - floor(x)
> > - ceiling(x)
> > - round(x, digits = 0)
> > - And possibly signif(x, digits = 6)
> >
> > The purpose would be to allow S3 methods to add additional arguments as
> > required.
> >
> > A few arguments in favor of this change:
> >
> > `trunc(x, ...)` already takes dots, which sets a precedent for the others
> > to do so as well. It is documented in the same help file as the other
> > rounding functions.
> >
> > Internally at the C level, a check is done to ensure that there is exactly
> > 1 arg for floor() and ceiling(), and either 1 or 2 args for round(). The
> > actual names of those arguments are not checked, however, and I believe
> > this is what allows `round.Date(x, ...)` and `round.POSIXt(x, unit)` to
> > exist, solely because they have 2 arguments. It seems like this is a bit of
> > a hack, since you couldn't create something similar for floor, like
> > `floor.POSIXt(x, unit)` (not saying this should exist, it is just for
> > argument's sake), because the 1 argument check would error on this. I think
> > adding `...` to the signature of the generics would better support what is
> > being done here.
> >
> > Additionally, I have a custom date-like S3 class of my own that I would
> > like to write floor(), ceiling(), and round() methods for, and they would
> > require passing additional arguments.
> >
> > If R core would like to make this change, they could probably tweak
> > `do_trunc()` to be a bit more general, and use it for floor() and
> > ceiling(), since it already allows `...`.
> >
> > A few references:
> >
> > Check for 1 arg in do_math1(), used by floor() and ceiling()
> >
> > https://github.com/wch/r-source/blob/fe82da3baf849fcd3cc7dbc31c6abc72b57aa083/src/main/arithmetic.c#L1270
> >
> > Check for 2 args in do_Math2(), used by round()
> >
> > https://github.com/wch/r-source/blob/fe82da3baf849fcd3cc7dbc31c6abc72b57aa083/src/main/arithmetic.c#L1655
> >
> > do_trunc() definition that allows `...`
> >
> > https://github.com/wch/r-source/blob/fe82da3baf849fcd3cc7dbc31c6abc72b57aa083/src/main/arithmetic.c#L1329-L1340
> >
> > - Davis
> >
>
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>
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