This is the inconsistency I am talking about:
> getClass("POSIXt")
Virtual Class
No Slots, prototype of class "NULL"
Extends:
Class "POSIXct", directly
Class "oldClass", by class "POSIXct"
> getClass("POSIXct")
Virtual Class
No Slots, prototype of class "NULL"
Extends: "oldClass"
Known Subclasses: "POSIXt"
> getClass("POSIXlt")
Error in getClass("POSIXlt") : "POSIXlt" is not a defined class
But to quote from the online help:
"POSIXct" is more convenient for including in data frames, and "POSIXlt" is
closer to human-readable forms. A virtual class "POSIXt" inherits from both
of the classes: it is used to allow operations such as subtraction to mix
the two classes.
In a S4 world wouldn't make more sense for POSIXt to be a virtual superclass
and POSIXct and POSIXlt to be subclasses?
But I think you have answered my other question about the future of s3.
> -----Original Message-----
> From: Prof Brian Ripley [mailto:[EMAIL PROTECTED]
> Sent: 05 August 2003 19:05
> To: Marsland, John
> Cc: [EMAIL PROTECTED]
> Subject: Re: [Rd] s4 methods and base
>
>
> On Tue, 5 Aug 2003, Marsland, John wrote:
>
> > I'm sure that many people are in the same position as me in
> that they are
> > trying to write packages and code that is vaguely "future proof".
> >
> > Would it be possible to get some guidance on how the R-core
> team see the
> > evolution of the "base" package with regard to s4 methods.
> >
> > There seem to be quite a lot of inconsistencies between s3
> and s4 methods
> > and classes currently and this (I'm sure) is only to be
> expected in a period
> > of transition. eg POSIXlt vs POSIXt and POSIXct. And there
> seem like dozens
>
> Those are S3 classes, and there is nothing transitional about them!
> There are no S4 classes in `base R' that I am aware of to be
> inconsistent.
> Are you sure you understand the difference?
>
> > of print methods to convert
>
> First you need to define S4 classes, and there are currently
> no moves to
> do that for the statistical modelling software, for example.
>
> > - it's not an enviable task and I'm sure it will
> > take time! ... if indeed you do see R being purged of s3 by
> some point in
> > the future.
>
> We are still using S3 classes designed a decade ago, and I
> expect to be
> still using them in another decade. I even have S4 versions
> of some of
> them (e.g. lda, multinom) and no plans to use those in R.
>
> --
> Brian D. Ripley, [EMAIL PROTECTED]
> 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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