[R] Defining class as a member of another class

[Wacek Kusnierczyk]

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.

vQ