Greg Ewing wrote:
Paul Moore wrote:
I'd rather see a solution which addressed the wider visitor use case (I think I just sprained my back bending over backwards to avoid mentioning generic functions :-))
Speaking of generic functions, while thinking about the recent discussion on proxy objects, it occurred to me that this is something you can do with an OO system that you can't do so easily with a generic function system. If the operations being proxied were generic functions rather than methods, you'd have to override them all individually instead of having a central point to catch them all.
I don't think it would actually be that much worse - something like typetools.ProxyMixin would just involve a whole series of register calls instead of method definitions. I wouldn't expect the total amount of code involved to change much.
That said, a recursive flatten() implementation is indeed a problem that generic functions are well suited to solving - have the default implementation attempt to iterate over the passed in object yielding its contents, yielding the object itself only if iteration fails, and then, for the types the application wishes to consider atomic, register an alternative implementation that just yields the object without attempting to iterate over it.