Re: [Rd] attributes of environments

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Wed 05 Jul 2006 - 20:18:21 GMT

On 7/5/2006 3:47 PM, Gabor Grothendieck wrote: > On 7/5/06, Duncan Murdoch <murdoch@stats.uwo.ca> wrote:
>> On 7/5/2006 2:23 PM, Gabor Grothendieck wrote:

>> I think by this time I have shown that subclassing of
>> > environments does not work yet it could if it were designed differently
>> > and furthermore there are significant problems with the workarounds.
>>
>> I don't think you've shown that subclassing of environments doesn't
>> work. You have an example that shows that shows that R implements
>> Henrik's "Case 2" rather than his "Case 1", but as Thomas and I said,
>> that really has nothing to do with subclassing.
>>
>> Subclassing is about defining a new class, not about copying objects.
>> You can (and did!) define a new class which inherits from the
>> environment class.

> 
> But by subclassing in the way allowed one comes up with something that
> is not useful.

You haven't shown that. Show an example where you define a new class that should inherit from environment but doesn't.

All you've shown so far is that when you try to change the class of an object to a new class, it appears that the class of another object also changes. (The explanation being that they are really just different names for the same object.)

> That is why tcltk and Henrik's package wrap environments in lists and define
> a completely different class but by doing that they are not able to take
> advantage of inheritance.

I think they did that because they wanted explicit references to objects, rather than the built-in implicit ones. I've wanted explicit references to things on a number of occasions too, but that's really unrelated to inheritance as far as I can see.

Duncan Murdoch



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