Re: [Rd] (PR#7320) Internal function isUME() in findGeneric() is wrong

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Sat 30 Oct 2004 - 04:43:01 EST


On Fri, 29 Oct 2004, Jeffrey J. Hallman wrote:

> OK, I looked at the documentation and you're right about that. However,
> I'm curious about why the first argument to UseMethod is ever necessary.
> Is there ever a good reason for it to be something other than the name
> of the calling function? (Wouldn't that lead to confusing code?) If
> not, why bother with it at all?

Yes. See coefficients(), fitted.values(). Also, you can have anonymous functions in R, operator functions ....

>
> I've become spoiled by programming a lot recently in Smalltalk, which is
> the cleanest language I've used yet.
>
> Jeff
>
>
> Prof Brian Ripley <ripley@stats.ox.ac.uk> wrote:
>
> br> The issue is the use of UseMethod(), which you claim to be valid. As it
> br> is inconsistent with the prime documentation, the help page, I would
> br> question if it is `perfectly legal'. I expect the author of isUME
> br> implemented the behaviour described on the help page.
>
> br> It is documented in S-PLUS as *strongly discouraged*, and although it is
> br> documented in R-lang, I believe the right thing to do is to make the code
> br> agree with the prime documentation.
>
> br> I see no uses of UseMethod() in the R sources, and on CRAN only
> br> one in a comment (and none in BioC).
>
> br> On Thu, 28 Oct 2004 jhallman@frb.gov wrote:
>
> >> Full_Name: Jeff Hallman
> >> Version: 2.0
> >> OS: Linux
> >> Submission from: (NULL) (132.200.32.34)
> >>
> >>
> >> The function findGeneric() in the utils namespace contains this internal
> >> function:
> >>
> >> isUME <- function(e) {
> >> if (is.call(e) && (is.name(e[[1]]) || is.character(e[[1]]))) {
> >> switch(as.character(e[[1]]), UseMethod = as.character(e[[2]]),
> >> "{" = isUMEbrace(e), "if" = isUMEif(e), "")
> >> }
> >> else ""
> >> }
> >>
> >> This fails if the generic called UseMethod() without an argument, which is
> >> perfectly legal. Changing it to this seems to work:
> >>
> >> isUME <- function(e) {
> >> if(is.call(e) &&(is.name(e[[1]]) || is.character(e[[1]]))) {
> >> switch(as.character(e[[1]]),
> >> UseMethod = ifelse(length(e) == 1, fname, as.character(e[[2]])),
> >> "{" = isUMEbrace(e),
> >> "if" = isUMEif(e),
> >> "")
> >> }
> >> else ""
> >> }
> >>
> >>
> >> Jeff
> >>
> >> ______________________________________________
> >> R-devel@stat.math.ethz.ch mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>
> >>
>
> br> --
> br> Brian D. Ripley, ripley@stats.ox.ac.uk
> br> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
> br> University of Oxford, Tel: +44 1865 272861 (self)
> br> 1 South Parks Road, +44 1865 272866 (PA)
> br> Oxford OX1 3TG, UK Fax: +44 1865 272595
>
>
>

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Sat Oct 30 04:57:51 2004

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