[Zope] Zope and Polymorphism

[Tres Seaver]

Ingo Assenmacher wrote:
> 
> Hi Tres!
> 
> Am 10-Feb-00 schrieb Tres Seaver:
> > Or, as an alternative, we could extend the <dtml-in> tag to pass in a filter
> > expression as an additional argument::
> >
> >   <dtml-in name=objectValues filter="self.hasMetaType( 'Document' )">
> >
> > The implementation would likely need to construct a Python code object by
> > synthesizing a function around the expression
> 
> That would be absolutely ok of course. Can I be of any help?

On further thought, this is better solved by repeating 

 <dtml-forever>
  <dtml-mantra> Separate content from presentation! </dtml-mantra>
 </dtml-forever>

More seriously, PythonMethods are the Right Thing (TM) here.  For example::

  PM ID:        folderishOnly
  Parameters:   self
  Body:
  ------------------------------
  result = []
  for obj in self.objectValues():
      if obj.isPrincipiaFolderish:
         result.append( obj )
  return result
  ------------------------------

Then I write in DTML:

  <dtml-in folderishOnly>
  </dtml-in>

This is better, by almost any criteria, than mangling the filter expression into
the <dtml-in> tag.

P.S.:  This would be even cooler, except PythonMethods don't have map/filter
available:

  return _.filter( isPrincipiaFolderish, self.objectValues() )

Actually, given _.filter, one could do this in DTML:

  <dtml-in expr="_.filter( isPrincipiaFolderish, self.objectValues() )">
-- 
=========================================================
Tres Seaver         tseaver@palladion.com    713-523-6582
Palladion Software  http://www.palladion.com