[Python-Dev] PEP 246: lossless and stateless

[Clark C. Evans]

On Thu, Jan 13, 2005 at 08:08:43PM -0500, Bob Ippolito 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)
| >
| >Then, Guido's 'Optional Static Typing',
| >
| >     def f(X: Y):
| >         pass
| >
| >   would be equivalent to
| >
| >      def f(X):
| >          X = adapt(X,Y, stateless = True, lossless = True)
..
| 
| 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.

etrepum,
               True                             False

  stateless    adapter may not add              adapter may have its
               state beyond that already        own state, if it wishes
               provided by the object           but additional state is
                                                not required


  lossless     adapter must preserve and        adapter may discard 
               give all information which       information if it wishes
               the underlying object has


So, in this case, if your consumer doesn't care if the adapter is
stateless or not, just call adapt(), which defaults to the case
that you wish.

Is this a better explanation?  Or is this whole idea too convoluted?

Best,

Clark