Stephen Colebourne wrote:Thinking about this some more, the semantics of keySet() would be difficult with "CompositeMap" approach that I have suggested above. We would either have to require that T be idempotent - i.e., T(T(x)) = T(x) or have the user supply a (partial) inverse transformer to return *a* pre-image for each transformed key.
I would like to propose an alternative solution to the problem that IMO fits
well with current [collections] direction.
Consider a new Map implementation that acts as a direct replacement for
HashMap, call it HashMapA (A for apache ;-). This class contains basically
the same code as HashMap, although it must be written without using cut and
paste (ie from scratch - Sun licence issues).
HashMapA differs from HashMap in that the hashing algorithm and equals
comparison methods are dedicated protected methods. It then becomes easy for
a subclass to be written that compares keys using case insensitivity
(amongst other things). HashMapA would also have a mapIterator() method to
access the new map iterator concept.
Finally, there would probably need to be a MapA interface to allow access to
the map iterator.
I see this more like Janek does -- the CaseInsensitiveHashMap requirement is really a key transformation requirement, not a hashing algorithm overriding requirement. I think that it would be *much harder* for users of this class to develop well-performing (and reliable) custom hash functions than to supply key transformations. I may be misunderstanding your proposal. Please explain more and why in particular it would not be better to set up something similar to TransformedMap that does key transformations on get -- effectively making a composite map, M o T, where T is the tranformer. The value of this is when T is not 1-1, as in the case of CaseInsensitiveHashMap.
Phil
Phil
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