[Zope-dev] Why are ZClasses bad?

[Joachim Werner]

Hi!

I guess ZClasses are not "evil" or so. But as somebody who has worked with
ZClasses for a long time and then switched to Python Products instead, I see
a lot of problems/disadvantages ZClasses have:

- Most important: It is rather hard to change the base classes with
ZClasses. In Python, you can do that very easily.

- Copy&paste programming does not work with ZClasses. With Python Products,
I can start writing my own version of an existing Product by just searching
and replacing all the occurences of the original Product name by my own one.
With ZClasses, copying an existing ZClass and changing it to fit will not
work well.

- If you use a decent editor (I am currently using PythonWin on Windows), it
is much more convenient to have all the methods of your class in just one
file than having to drill down into the ZMI and search for individual
Scripts (Python) or DTML Methods

- Debugging Python code is easier than debugging ZClasses. E.g., you can use
a real debugger, or just add temporary print statements to the code. With
Python code, the tracebacks are much more helpful than they are with
ZClasses, especially if you use DTML ...

- Working from Python gives you MUCH more power, and the code usually is
more compact.

- You can use CVS for the code, and there is a rather strict separation
between instances of your Product/class and the code ...

- ZClasses behave "strange" with regard to nested acquisition. I experienced
cases where two instances of a ZClass acquired from each other in a way they
shouldn't ...

- ZClasses are relatively slow, especially if you use other ZClasses as base
classes of ZClasses.

One of the great disadvantages of Python-based Products was that you had to
permanently restart your Zope to see the changes in action. But now we have
"refresh", which works great.

That said, I can still imagine using ZClasses together with a custom-built
Python-based base class. They are over-the-web, which is their greatest
advantage.

For Zope 3, I'd suggest a complete redesign of ZClasses to offer something
similar without the disadvantages ...



----- Original Message -----
From: "Dario Lopez-Kästen" <dario@ita.chalmers.se>
To: <zope-dev@zope.org>
Sent: Wednesday, April 03, 2002 11:20 AM
Subject: [Zope-dev] Why are ZClasses bad?


Hello!

I keep hearing people argue that ZClasse are bad, and I am curious as to why
they are.

I recall something about ZClasses and the catalog, but are there any other
"badness" with ZClasses?

/dario - curious

- --------------------------------------------------------------------
Dario Lopez-Kästen, dario@ita.chalmers.se        IT Systems & Services
System Developer/System Administrator     Chalmers University of Tech.



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