[Zope3-Users] How to manually define an object's provided interfaces?

[Frank Burkhardt]

Hi,

On Mon, May 29, 2006 at 01:31:03PM +0200, Lennart Regebro wrote:
> On 5/29/06, Frank Burkhardt <fbo2 at gmx.net> wrote:
> >I'm going to write an alternative implementation of
> >zope.app.file.interfaces.IFile . This implementation will automatically
> >determine the mime type of the data it's containing.
> >
> >I would like to add a method that determines (guesses), if the current file
> >object contains an image...
> >
> > isimage=(mimetype(self.data).split('/')[0] == 'image')
> >
> >... and I want to dynamically make the object implement another interface ...
> 
> Ehhh. Really? I must say that I find that a very suspiscious way of
> handling that problem. Rather I would use a factory that generates the
> correct type of object (image or file) from the data.

Different factories won't help because the user should be able to update
the file object's content after ist was created.

> > if isimage:
> >    IImage.provide(self)
> > else:
> >    IImage.dontprovide(self)
> >
> >Unfortunately, there is no 'provide' method on interfaces :-( .
> 
> Of course, you don't want to make an interface dynamically be another
> interface, that just doens't make any sense. You could probably do it
> by making the OBJECT provide different interfaces dynamically.

OK - this was a bit confusing. One more try:

 I want to make an object provided one interface (IFile) always and one
 interface (IImage) "sometimes". Sometimes means "whenever libmagic thinks,
 the file is an Image". I don't want to modify any interface but only the
 object's list of provided interfaces.

Regards,

Frank