Hi all,
Thanks for the reply, Lloyd.
Lloyd Kvam said unto the world upon 2005-03-17 20:36:
You want a method in a base class to parse input and create instances of certain derived classes.
Not quite. One class (Tree) parses a file and creates instances of Node1 and Node2 (derived from Node). None of the Node classes inherit Tree. But I don't think that difference matters for what you suggested. :-)
Your sample code looks like: if some_condition_on_chunk_contents: node = Node1(chunk_contents) else: node = Node2(chunk_contents)
I'd suggest changing the method to use a variable to determine the class. Following your pattern of coding: #Toolkit.py class Tree: node1 = Node1 node2 = Node2 ... class Node1(Node): ...
#Application.py class Tree(Toolkit.Tree):
<SNIP -- same as in Tree immediately above>
if some_condition_on_chunk_contents: node = self.node1(chunk_contents) else: node = self.node2(chunk_contents)
This requires that the class constructors be similar enough so that they
take the same parameters.
Happily, the interfaces are identical. :-) (I need different Node classes as the chunk_contents are in different formats, the tasks are the same, modulo differences due to format.)
It is also a manual effort to keep the node assignments in Tree in sync with the Node classes that you write. You also face a similar issue keeping Application.py and Toolkit.py in sync.
Hmm. I think I do see some appeal to the route you suggest, but I'm feeling unhappy about the need to keep multiple things in sync.
I think I will play with this and other alternatives and see what feels right. Thanks so much for the input :-)
Best to all,
Brian vdB
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