This past September, Phillip Eby and I discussed a variety of ZConfig
issues on one list or another.  Two particular issues I've thought
more about, and think I'm reversing myself on them.  ;-)

I'm going to describe each issue in a separate email, including why
I've changed my mind about them and what the consequences are for
ZConfig users.  Please respond to these messages if you think the
proposed changes will have a negative impact on working code.

"Inheritance" of the datatype when extending a section type

Currently, ZConfig section types that "extend" another do not inherit
the datatype of the type they extend.  Phillip argued that, at least
for schema extensions, the datatype should be inherited from the base

I thought it better to explicity request the same datatype was a
better approach because of way we've been using ZConfig in some of the
core packages.  Each concrete section type really uses a different
datatype; sharing configuration handling is accomplished only within
Python.  When this is the only way section types are being used,
explicit is the only way to do things.

While trying to create some fairly basic section types that are easy
to specialize using extension, this can be less than desirable.  What
it boils down to is that it's difficult to create section types that
can be easily specialized with a minimum of additional information in
the schema; a fair bit of boilerplate is needed to change a small
amount of behavior.

If we add inheritance of the datatype for section types, this affects
only section types that extend another section type where the "base"
specifies a datatype and the derived type does not; in that case, the
datatype of the base will be used instead of the "null" datatype.  If
the "null" datatype is needed, section types that expect it to be used
can add the attribute datatype="null" to achieve the current effect
(in fact, that works now).

No existing unit tests are affected.


Fred L. Drake, Jr.  <fred at>
PythonLabs at Zope Corporation

Zope-Dev maillist  -  [EMAIL PROTECTED]
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