[Zope3-dev] Re: proposal: replace zope.schema.Sequence with zope.schema.Collection

[Fred Drake]

On Wednesday 28 April 2004 03:28 pm, Gary Poster wrote:
 > In zope/schema/_field.py, Stephan implements Sequence, then subclasses
 > Sequence for Tuple, List, and Set.  This is ok, since its
 > implementation, but ISet also subclasses ISequence, which is wrong
 > (since a set is not a sequence: it is not ordered).

Definately!

 > IMO, Stephan has identified a clear place in which our model could be
 > improved.  Rather than merely making ISet not subclass ISequence (and
 > make it just subclass IField, I suppose), I propose that
 >
 >     * "Sequence" be renamed to "Collection" (and "ISequence" to
 >       "ICollection");
 >     * "Collection" include an "ordered=True" keyword argument;
 >     * "List" and "Tuple" subclass "Collection" (and same for interfaces)
 >       and disallow setting of "ordered" (it must always be True);
 >     * "Set" subclass "Collection" (and same for interfaces) and disallow
 >       setting of "ordered" (it must always be False); and
 >     * (less importantly) "Set" default to creating a Sets.set.

I just spoke with Gary, and am proposing a slight modification of this change:

- Collection is added as a base for Sequence (and ICollection for ISequence)

- Sequence will set ordered=True and disallow changing it

- List and Tuple subclass Sequence

 > I'll give this a whirl unless someone stops me.  Thoughts?

Some days, yes.


  -Fred

-- 
Fred L. Drake, Jr.  <fred at zope.com>
PythonLabs at Zope Corporation