Using descriptors

[Andróg i Ngaurwaith]

Mike Fletcher <mcfletch at rogers.com> wrote in message news:<cAUv9.119528$Q3S.60747 at news01.bloor.is.net.cable.rogers.com>...
> You haven't, in your example, used any descriptors (explicitly).  A 
> descriptor would (for instance) automatically wrap whatever was stored 
> in "testMethod" with the appropriate pre and post conditions.  For 
> instance, a staticmethod descriptor wraps a function for access such 
> that the function is returned un-changed, a classmethod wraps a function 
> for access such that the function is passed a pointer to the class when 
> called, etceteras.

Hmm... I don't really understand the distinction. What is it about
descriptors that make them different from other classes (such as I
used in the example)? To aid my understanding, would it be possible
for you to give a definition for or some code illustrating this
"wrapping"?

> Assume we have a hypothetical pre and post condition descriptor class:
*snip*
> Now, the descriptor would automatically wrap the methods (do_x, do_y) 
> with a PrePostMethod wrapper (which would take 3 args, pre, post and 
> method) when they were accessed as O().x or O().y, and they would do 
> that wrapping _even for new methods/functions/instances_ if you include 
> set functionality in your "prepostmethod" descriptor class.

I may sound dense, but I really don't understand what you're getting
at here with "they would do that wrapping _even for new
methods/functions/instances_" I can't make any sense out of this
explanation.

> Realistically, though, pre and post conditions for _methods_ are 
> probably best done with asserts at the start and end of the method-body; 
> far less overhead at run-time.

Pre- and post-conditions are not actually what I'm after here; I'm
trying to implement a way of transparently getting information (method
name, parameters) about some method calls (for uses such as logging,
etc), without having to add the code into the method.

Andrew