Getting derived classes

[Robert Fraser]

Bruno Medeiros wrote:
> Getting that information at *runtime* might be sensible, but I'm not 
> seeing much usefulness in that.

The main use case I can see is a plugin solution. For example, 
automatically instantiate all classes that extend IPlugin or something. 
However, requiring a config file that includes the class name and maybe 
some metadata isn't too hard to do and is potentially more efficient.