"Michele Simionato" <[EMAIL PROTECTED]> writes:
> adding methods on the fly and metaclasses could live pretty well
> without
> multiple inheritance. There would be no real loss
> of power and hopefully less monstruosities such
> a Zope 2. But maybe this is just wishful thinking ...
Um, no real loss of power? Well, in the sense that all languages are
turing-equivalent, maybe.
My current project includes a small set of classes that all deal with
web pages. The classes exist in three layers: the first layer is very
abstract, and provides a general mechanism. The second layer adapts
the general mechanasm to a specific case. The last layer provides
application-specific functionality. The classes intercommunicate, but
are generally completely unrelated to each other except for the more
concrete classes inheriting from the layer above.
So far, so good - it's all simple single inheritance.
Now, I have a class Utility that collects utility methods that are
useful for dealing with web pages: extracting data, filling out forms,
etc. These are provided as a mixin. The classes that need this
functionality inherits from it as well as their parent. The classes
that don't need it don't. This makes use of multiple inheritance.
Without multiple inheritance, I would have had to make the Utility
class a parent of all the most abstract classes. Some of the those
classes don't need that functionality - but their children do, so they
have to inherit from it. Children's needs shouldn't influence the
implementation of the child - that's simply ugly. Also, it creates an
apparent relationship between all the most abstract classes that
doesn't really exist.
Do you have a proposed solution that doesn't have these problems?
<mike
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Mike Meyer <[EMAIL PROTECTED]> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.
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