Wacek Kusnierczyk wrote:
Martin Morgan wrote:
Gabor Grothendieck wrote:
Try this:
setClass("zoo")
[1] "zoo"
'zoo' is I guess intended as an S3 class (from library zoo), so
setOldClass('zoo') is appropriate. Otherwise, setClass("zoo") creates a
new virtual class.
setClass("Work",representation=(x="zoo"))
This syntax representation=(x="zoo") is doing something quite strange;
Strange? If there's is something strange here, it's is the idea that
setClass('bar', representation=c('foo'))
creates a subclass of 'foo', while
setClass('bar', representation=c(x='foo'))
creates a class with 'foo' as a component. it's just a design choice,
but it's confusing and surely begging for trouble. but given this is as
it is, there is nothing strange with
setClass('bar', representation=(x='foo'))
as far as i am able to understand r, it's equivalent to
x = 'foo'
setClass('bar', representation='foo')
hence, bar extends foo. just a little and useless pattern.
Yes, assuming standard evaluation. I think the point was that if you
were expecting it to generate a slot "x", then setClass() would need to
do something strange internally -- recognizing the assignment and
deparsing its LHS for the component name.
Having results depending on whether or not a character vector is named
does look like an accident waiting to happen, I agree. However, as of
2.9.0, Martin's code doesn't seem to actually work:
> setClass("Work",representation=c(x="integer"))
Error in validObject(.Object) :
invalid class "classRepresentation" object: invalid object for slot
"slots" in class "classRepresentation": got class "character", should be
or extend class "list"
The documentation says that representation is a named _list_, so you'd
want representation=list(x="integer") to get slot "x".
The actual implementation does have
if (is.character(representation) && length(representation) ==
1L && is.null(names(representation)))
representation <- list(representation)
which is what allows representation="integer" to work. IIUC, this is a
compatibility feature for a compatibility feature.
--
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~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907
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