On 28/03/2008, at 3:23 AM, Ken Thomases wrote:
On Mar 26, 2008, at 11:43 PM, Graham Cox wrote:
I have a class that can contain different objects which all derive
from a class R. The container can accept instances of any subclass
of R.
Each subclass of R implements a CLASS method for a particular
feature, returning an array. The container needs to build an array
which is the union of all the arrays returned by each subclass.
Thus it needs to iterate through a list of all possible subclasses
of R, combining the arrays as it goes. Problem is that not all
possible subclasses of R are known until runtime, so I need a way
to be able to get hold of such a list, based on the fact that they
all inherit from R. Note that these are not instances of R, but
classes. (I can get a list of instances I have right now, but that
doesn't cover the possibility of another object instance derived
from R being added after I already built the array).
Hope this makes sense - any ideas?
You seem to have solved this, but there might be a better way:
Implement +initialize on class R. Reading the docs on +initialize,
you'll find that it's called for subclasses of R, too, if those
subclasses don't override +initialize. Even if a subclass does
override +initialize, you can make it a part of the design contract
that they must call [super initialize]. (Yes, that goes against a
suggestion in the docs, but in this case you're doing it with eyes
open for a specific purpose.)
So, now you have arranged that R's +initialize is called for R and
every one of its subclasses. In that method, you can use "self" to
refer to the actual (sub)class being initialized and do whatever is
appropriate from there.
The problem with using initialize is that it's only guaranteed to be
sent just before the first message is sent to that class (which might
not be at all if the class isn't used).
- Chris
_______________________________________________
Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to [EMAIL PROTECTED]
