[Python-Dev] PEP 246, redux

[Alex Martelli]

On 2005 Jan 12, at 20:39, Phillip J. Eby wrote:
    ...
>> > it's difficult because intuitively an interface defines a 
>> *requirement*, so
>> > it seems logical to inherit from an interface in order to add 
>> requirements!
>>
>> Yes... I would fall into this trap as well until I'd been burned a 
>> few times.
>
> It's burned me more than just a few times, and I *still* sometimes 
> make it if I'm not paying attention.  It's just too easy to make the 
> mistake.  So, I'm actually open to considering dropping interface 
> inheritance.

What about accepting Microsoft's QueryInterface precedent for this?  I 
know that "MS" is a dirty word to many, but I did like much of what 
they did in COM, personally.  The QI precedent would be: you can 
inherit interface from interface, but that does NOT intrinsically imply 
substitutability -- it just means the inheriting interface has all the 
methods of the one being subclassed, with the same signatures, without 
having to do a nasty copy-and-paste.  Of course, one presumably could 
use NO_ADAPTER_NEEDED to easily (but explicitly: that makes a 
difference!) implement the common case in which the inheriting 
interface DOES want to assert that it's perfectly / losslessly / etc 
substitutable for the one being inherited.


Alex