On Thu, 11 May 2006, Parlamis Franklin wrote:
> Using the '@' operator, I am able to extract a 'names' attribute
> assigned to a formal object.
> However, I can not use the replacement form ('@<-') to assign that
> attribute.
>
> > setClass("foo", representation("numeric"))
> [1] "foo"
> > (new("foo", 1:4)->a)
> An object of class ?foo?
> [1] 1 2 3 4
> > names(a) <- LETTERS[1:4]
> > [EMAIL PROTECTED]
> [1] "A" "B" "C" "D"
> > [EMAIL PROTECTED] <- LETTERS[5:8]
> Error in checkSlotAssignment(object, name, value) :
> "names" is not a slot in class "foo"
>
> I don't know that this asymmetry will ever cause a problem, but I
> just wanted to note it because it appears from the help pages
> 'slot {methods}' and 'slotOp {base}' that the '@' operator is only
> intended to provide access to defined slots.
Yes, it is intended so. It is a side effect of the current implementation
that @ will also access attributes, but that may change. Note that the
help page for @ says
These operators support the formal classes of package 'methods'.
See 'slot' for further details. Currently there is no checking
that the object is an instance of a class.
so this should not come as a surprise to you.
--
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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