[Python-Dev] Looking for master thesis ideas involving Python

Phillip J. Eby pje at telecommunity.com
Thu Oct 30 12:37:24 EST 2003

At 01:43 PM 10/30/03 +0100, Samuele Pedroni wrote:
>- multi methods cover some ground also coverd by interfaces and adaptation:
>   *) a generic function/multi method is also an interface
>   *) some of the things you can achieve with adaptation can be done with 
> multi methods
>Once you have multimethods do you still need adaptation in some cases or, 
>could one obtain the functionality otherwise or do you need dispatch on 
>interfaces (not just classes), how would then interfaces look like and the 
>dispatch on them?

With a sufficiently powerful predicate dispatch system, you could do away 
with adaptation entirely, since you can simulate interfaces by implementing 
a generic function that indicates whether a type supports the interface, 
and then defining a predicate type that calls the generic function.

That is, I define a predicate type IFoo such that ob is of type IFoo if 
'implementsIFoo(ob)'.  Then, for any type that implements the interface, I 
define a multimethod saying that implementsIFoo() is true for objects of 
that type.  Then, I can declare multimethod implementations for the IFoo 
predicate type.

What I'm curious about is: is there any way to do it *without* predicate 
types?  Could you have an "open ended union" type, that you can declare 
other types to be of, without having to inherit from a base type?

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