[Python-Dev] PEP 246: lossless and stateless

[Bob Ippolito]

On Jan 13, 2005, at 20:03, Clark C. Evans wrote:

> Ok.  I think we have identified two sorts of restrictions on the
> sorts of adaptations one may want to have:
>
>   `stateless'  the adaptation may only provide a result which
>                does not maintain its own state
>
>   `lossless'   the adaptation preserves all information available
>                in the original object, it may not discard state
>
> If we determined that these were the 'big-ones', we could possibly
> allow for the signature of the adapt request to be parameterized with
> these two designations, with the default to accept any sort of adapter:
>
>    adapt(object, protocol, alternative = None,
>          stateless = False, lossless = False)
>
>    __conform__(self, protocol, stateless, lossless)
>
>    __adapt__(self, object, stateless, lossless)
>
> Then, Guido's 'Optional Static Typing',
>
>      def f(X: Y):
>          pass
>
>    would be equivalent to
>
>       def f(X):
>           X = adapt(Y, True, True)
>
> In other words, while calling adapt directly would allow for any 
> adapter;
> using the 'Static Typing' short-cut one would be asking for adapters
> which are both stateless and lossless.  Since __conform__ and __adapt__
> would sprout two new arguments, it would make those writing adapters
> think a bit more about the kind of adapter that they are providing.
>
> Furthermore, perhaps composite adapters can be automatically generated
> from 'transitive' adapters (that is, those which are both stateless
> and lossless).  But adaptations which were not stateless and lossless
> would not be used (by default) in an automatic adapter construction.
>
> Your thoughts?

In some cases, such as when you plan to consume the whole thing in one 
function call, you wouldn't care so much if it's stateless.

-bob