[Zope] ZClasses

[Dieter Maurer]

Eddy Ilg wrote at 2004-10-1 09:51 +0200:
>I am getting started with Zope and really enjoying it. I am reading the 
>Zope book and tumbled over this comment:
>
>Anonymous User - Apr. 29, 2004 10:57 am:
>According to the ZopeWiki, you should NEVER use ZClasses. 
>http://www.zopewiki.org/ZopeDosAndDonts
>
>Anonymous User - Sep. 25, 2004 1:10 pm:
>  Why do I learn about ZClasses if I am not supposed to use them? (I 
>checked zopewiki, it really says you
>  aren't supposed to!)
>
>
>Should I use ZClasses? If not what should I use instead?

There are strong differences in the opinion about "ZClasses".

There are still and have been (in the past) some problems
with ZClasses. Due to these problems, some people think,
ZClasses should not be used. I do not share this opinion.

The problem that is still there: you must not inherit
from a ZClass defined in a different product. While
it apparently work in the first place, it will break as soon
as you export your product (the link between deriving and
base class is lost). That is nasty, if you are unaware.

There are thousands of unit tests for Zope. These unit
tests ensure, that the likelyhood it high, that Zope still
works in new releases. However, there are almost no unit
tests for ZClasses. As a result, ZClasses broke often
between releases. Usually, it was only a minor issue --
but maybe, too large that you could fix it yourself.

These are the (known) risks.


I used to use ZClasses for large projects -- and did not make
bad experiences. It is very easy to integrate standard Zope
objects in your own ZClasses to create new applications.
I even created abstract ZClasses and mixin classes. All worked very well.


Nowadays, I no longer use ZClasses. We moved over to the CMF and
Archetypes. They provide similar bundling features as ZClasses,
are much more efficient (with respect to runtime) and
the code is maintained in the file system and thereby subject
to standard revision processes. The latter is essential
for really large projects.
You must learn a lot when you want to follow this route --
much more than when you use ZClasses.


To summarize: when you are still learning or you make smaller
prototypes, you can use ZClasses.
For long living projects or (runtime) resource critical applications,
file system based code is superior. It is faster and can be
revision/source controlled.

-- 
Dieter