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.
I hope that's useful,
Ken
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