[Python-3000] Abilities / Interfaces

[Phillip J. Eby]

At 04:06 PM 11/21/2006 -0800, Guido van Rossum wrote:
>On 11/21/06, Nestor <nestornissen at gmail.com> wrote:
> > Do these aproaches allow to do something like the
> > java.util.RandomAccess interface that is just used as a marker?
>
>Zope interfaces certainly do. I don't know about Phillip's
>counter-proposal.

If we're basing GF's on types, then certainly marker mixins are feasible to 
*use*.  I only contend that mixin markers (and other pure interfaces devoid 
of execution effect) are unnecessary and shouldn't be encouraged, not that 
they are or should be impossible.


>  With ABCs it would seem that one has to plan this
>ahead of time (i.e., at class definition time), which isn't always
>reasonable.

For this reason, I would be against allowing *only* definition-time 
interface declarations.  A major benefit of both adaptation and generic 
functions is that they allow retrofitting or gluing of "oblivious" code; 
i.e., code that wasn't originally designed to work with the thing you're 
gluing it to.

Having only interfaces and introspection would also just mean that we are 
adding Java-like declarations and LBYLisms, without any improvements in 
expressive power or code clarity.  Declaring an interface or adding a mixin 
should *do* something, instead of simply being a comment in the form of 
code, that other code is able to read.  :)