R devel - Jun 2008 - is() and S3 classes

The is() function begins with the following code:

    cl <- class(object)
    if (length(cl) > 1) {
        if (is.na(match(cl[[1]],
names(getClass("oldClass")@subclasses))))
            return(class2 %in% cl)

As one can see, it uses S3 inheritance if the first element of the class
attribute is an "oldClass". In R prior to 2.7, is() would check S4
inheritance if any (not just the first) classes named in the class attribute
were derived from "oldClass".

It seems to me that S3 inheritance would imply that an R object is an
instance of "oldClass" if any of its classes are derived from
"oldClass".
Could the current behavior be changed, please?

Thanks,
Michael

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On Wed, Jun 4, 2008 at 8:05 PM, Michael Lawrence <mflawren@fhcrc.org>
wrote:
> The is() function begins with the following code:
>
>     cl <- class(object)
>     if (length(cl) > 1) {
>         if (is.na(match(cl[[1]],
names(getClass("oldClass")@subclasses))))
>
>             return(class2 %in% cl)
>
> As one can see, it uses S3 inheritance if the first element of the class
> attribute is an "oldClass". In R prior to 2.7, is() would check
S4
> inheritance if any (not just the first) classes named in the class
attribute
> were derived from "oldClass".
>
Sorry just checked and this is how it basically behaved pre R 2.7, so I
guess I withdraw my request ;)

> It seems to me that S3 inheritance would imply that an R object is an
> instance of "oldClass" if any of its classes are derived from
"oldClass".
> Could the current behavior be changed, please?
>
> Thanks,
> Michael
>
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