.Alias and memory

[Prof Brian Ripley]

> Date: Thu, 11 Mar 1999 09:37:53 +0000 (GMT)
> From: Jonathan Rougier <J.C.Rougier@durham.ac.uk>
> To: Paul Gilbert <pgilbert@bank-banque-canada.ca>
> 
> On Wed, 10 Mar 1999, Paul Gilbert wrote:
> 
> > In an effort to encapsulate my dependence on class in order to deal with
> > oldclass/class in Splus  I defined the functions
> 
> [ ... ]
>  
> > This last allows me to end a function definition with
> >   ...
> >   classed(somecalc, "whatever") }
> > 
> > rather than
> >   ...
> >   obj <- somecalc
> >   class(obj) <- "whatever"
> >   obj }
> 
> I may be missing the point, but it seems to me that you could achieve a
> `one-line return' using
> 
>     structure(somecalc, class = "whatever")
> 
> which would also avoid passing somecalc into another function.

In part you are. That is equivalent to

attr(somecalc, "class") <- "whatever"

and whereas that happens to be how class<- is defined on S3 and R, it
is not how it works in S-PLUS 5 (although oldClass<- is currently
defined that way).  When you want to change to S-PLUS 5-style classes
you have to remember that you have subverted the system!

More generally, using the representation not the public method in
object-oriented programming is a recipe for disaster.


-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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