Webware extensibility WAS: Re: [Webware-discuss] notify me when the session ends

[Jason H. <ja...@pe...>]

On Wed, 2004-02-25 at 13:37, Aaron Held wrote:
> Personally I would be against subclassing a 'core' class such as
> sessions,
> I would rather see some hooks for calling implementation specific
> code.

Hi Aaron,

I'm curious as to your rationale for preferring hooks over using subclasses
to do customization.  I keep my own copies of modified Webware source in CVS
(merging is a painful operation), so I'm interested in making Webware more 
extensibile too, but I'm unsure of how we can best achieve this.

<storytime>
Several years ago I wrote a framework in PHP which provided a lot of
callbacks for customization.  On problem I ran into is that depending on
how you need to customize, you might want to execute some code before,
instead of, or after an event:

    preCommit()
    commit()
    postCommit()

This led to a proliferation of callback functions which achieved the goal of
customizability, but had several shortcomings:

    - difficult to keep track of all the callback methods and their names

    - to maintain sanity, the three callbacks for an event (pre, the
      event itself, and post) need to have the same parameters, which
      means changing in three places

    - I ended up with a pile of 'bare' callback functions (not attached to a
      class), for which it would be difficult for someone else to understand
      the interplay.

I eventually realized that using classes would clean a lot of this up.
With classes you only need one method per event.  Any subclass which
overrides this method can call the superclass' method (or not) when it
needs to, thereby controlling whether the new functionality is executed
before, instead of, or after the event.
</storytime>

This is food for thought.  I'd like to hear more about what you envision for
a good way to make Webware extensible -- maybe we can make some progress on
this front.

peace,
Jason