Plugging in

After releasing z3c.pt I've had some inquiries as to whether it will be possible to plug in expressions like you can with zope.pagetemplate (currently only Python-expressions are supported). I'd like to try and shoot down this idea using zope.contentprovider as ammunition.

All non-trivial templates should be associated with a view. Hence, if we could agree on an easy way to lookup, instantiate and update content providers in a view without writing any code, I think we're set. It could look like this:

   class MyView(BrowserView):
      header = ContentProvider('plone.Header')

On class instantiation, all available content providers would be instantiated and updated such that we can call the ``render``-method directly from the template (i.e. view.header.render()).

This approach has the advantage that it's actually honoring the requirement that all content providers should be updated before they're rendered (see zope/contentprovider/tales.py:41).

Obviously, this argument doesn't apply to other kinds of expressions that one could wish to plug in. Perhaps the ``string`` expression is quite handy, but very much so only because TAL doen't allow interpolation. It could look like this:

   <a href="${item.getURL()}/folder_listing">
     Listing of all items in ${item.Title}
   </a>

There's a pattern here. Although it may seem like there's a real need for different kinds of expressions, it's really just symptom treatment. As part of our on-going effort to lower the entry bar for Zope-development, let's keep in mind that less is often more, a notion that easily extends to complexity.