[ZODB-Dev] Fwd: [Zope3-dev] directory hierarchy proposal (Martijn Faassen)

[Steve Alexander]

>   SA> Is there any reason why we have xI and xO versions of sets?
> 
>   SA> For example, IOTreeSet and IITreeSet would seem to work pretty
>   SA> much identically, except that they are different classes, and
>   SA> you get them as return values from methods of different kinds of
>   SA> BTree.
> 
>   SA> Is this just an implementation issue? Can this issue be hidden
>   SA> from users of the btrees module?
> 
> Tim says there is a reason for this, but he can't remember what it
> is.  Maybe Jim knows.  If you see him, can you ask him :-).

I asked Jim.

If I have this right, the official reason is that an xOSet has a 
different default weighting in a weighted set operation than an xISet.

The unofficial reason is that it made the code less complex to have 
separate classes for xISet and xOSet.

Personally, I'd be happy to require that the weighting is made explicit, 
  and have only ISet, OSet, ITreeSet, and OTreeSet.

--
Steve Alexander