I think Spencer's point of it likely being compatible with most current code is important (since it currently always returns 9 so its unlikely to be used meaningfully in existing code).
On 7/24/06, Martin Maechler <[EMAIL PROTECTED]> wrote: > So I did open a new subject and move the discussion to R-devel > now. > > >>>>> "MM" == Martin Maechler <[EMAIL PROTECTED]> > >>>>> on Mon, 24 Jul 2006 11:46:05 +0200 writes: > > >>>>> "Gabor" == Gabor Grothendieck <[EMAIL PROTECTED]> > >>>>> on Sun, 23 Jul 2006 09:02:35 -0400 writes: > > Gabor> Looking at the diff.POSIXt code we see the problem is > Gabor> that it takes the length of the input using length > Gabor> which is wrong since in the case of POSIXlt the > Gabor> length is always 9 (or maybe length should be defined > Gabor> differently for POSIXlt?). > > MM> Though I agree with Spencer that a user may expect > MM> length() to behave differently, but I don't think this > MM> would be a good idea. Yes, length() is generic, but its > MM> help() emphasizes that for lists, length() should be the > MM> number of list elements. Of course anyone one *can* > MM> define length() methods that behave differently for > MM> his/her classes, but then one would also want to make > MM> sure that e.g. x[length(x)] or 'x[length(x)] <- value' > MM> works and -- in a case of simple S3 class built on a > MM> list, would work differently than if x was a the simple list. > > Hmm, after thinking a bit more, and particularly after seeing > all the other methods we already have working for "POSIXlt", > I'm much less sure if (re)definining length(<POSIXlt>) > would be such a bad idea. > Indeed, "[", and "[<-" and "[[" already work with an implicit > length of 'length_of_series' and not length 9, and so does str(). > > So it seems to me, there is more reasonable momentum *for* a > length.POSIXlt() method than I first considered. > > Still not sure what the wisest decision would be, and I am > asking for more opinions or arguments pro / con. > Since Brian Ripley has done the most work on the POSIX[cl]?t > classes, we should also wait on his opinion. > > Martin > > MM> In my view, I would only consider redefing length() for > MM> "non-basic" S4 classes, i.e. those with slots, where no > MM> confusion is possible, since these objects are > MM> definitely not simple vectors nor lists (aka "generic" > MM> vectors). > > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
