Victor,
If you give a closer look to my example, you will notice a difference: > $map[$setA] and $map[$setB] point to the same storage which I think is not > possible with SPLObjectStorage. > Well, how could you do that? Without implementing object comparison methods at least (which is outside the scope of this discussion)? I could see a type-specific map which knows how to compare the classes, but in general you'd need to defer comparison to the objects themselves (so $obj1 == $obj2 would fire $obj1->compareTo($obj2) === 0)... Unless I've got something confused...
