[Zope3-Users] Interface confusion (still)

[Tim Cook]

On Tue, 2008-07-15 at 18:56 -0400, Benji York wrote:
> On Tue, Jul 15, 2008 at 6:31 PM, Tim Cook <timothywayne.cook at gmail.com> wrote:
> 
> >> Note: classes *implement* interfaces, their instances *provide* them.
> >
> > ... and I am still confused about a use case for classProvides.
> 
> When one says that a class *provides* an interface they're saying that
> instances of that class *implements* the interface.
> 
> On the other hand, lets say you had an IFooFactory interface that only
> required that objects *providing* it be callable.  In that case a class
> Foo itself can *provide* the interface (because the class is callable).
> 
> Make sense?

Hmmm, not really.  I tend to be VERY applied so how about an example
from Zope?

==========================================================================
class Maildir(object):
    """See `zope.sendmail.interfaces.IMaildir`"""

    classProvides(IMaildirFactory)
    implements(IMaildir)


class IMaildirFactory(Interface):

    def __call__(dirname, create=False):
        """Opens a `Maildir` folder at a given filesystem path.

...


class IMaildir(Interface):
    """Read/write access to `Maildir` folders.

    See http://www.qmail.org/man/man5/maildir.html for detailed format
    description.
    """

    def __iter__():
        """Returns an iterator over the pathnames of messages in this
folder.
        """

    def newMessage():
        """Creates a new message in the `maildir`.
=============================================================================

Now why wouldn't IMaildir just not inherit from IMaildirFactory instead
of from Interface?  If it did; what would be the effect of the
difference(s) in approach to the rest of the application?

Thanks,
Tim

  





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