[Python-Dev] PEP 246, redux

[Phillip J. Eby]

At 06:18 PM 1/12/05 +0100, Alex Martelli wrote:

>On 2005 Jan 12, at 17:40, Phillip J. Eby wrote:
>
>>At 04:36 PM 1/12/05 +0100, Alex Martelli wrote:
>>>I already know -- you told us so -- that if I had transitivity as you 
>>>wish it (uncontrollable, unstoppable, always-on) I could not any more 
>>>write and register a perfectly reasonable adapter which fills in with a 
>>>NULL an optional field in the adapted-to interface, without facing 
>>>undetected degradation of information quality by that adapter being 
>>>invisibly, uncontrollably chained up with another -- no error message, 
>>>no nothing, no way to stop this -- just because a direct adapter wasn't 
>>>correctly written and registered.
>>
>>But why would you *want* to do this, instead of just explicitly 
>>converting?  That's what I don't understand.  If I were writing such a 
>>converter, I wouldn't want to register it for ANY implicit conversion, 
>>even if it was non-transitive!
>
>[snip lots of stuff]
>I have some data about people coming in from LDAP and the like, which I 
>want to record in that SQL DB -- the incoming data is held in types that 
>implement IPerson, so I write an adapter IPerson -> IFullname for the purpose.

This doesn't answer my question.  Obviously it makes sense to adapt in this 
fashion, but not IMPLICITLY and AUTOMATICALLY.  That's the distinction I'm 
trying to make.  I have no issue with writing an adapter like 
'PersonAsFullName' for this use case; I just don't think you should 
*register* it for automatic use any time you pass a Person to something 
that takes a FullName.


>   So, I'm not sure why you appear to argue for conversion against 
> adaptation, or explicit typechecking against the avoidance thereof which 
> is such a big part of adapt's role in life.

Okay, I see where we are not communicating; where I've been saying 
"conversion", you are taking this to mean, "don't write an adapter", but 
what I mean is "don't *register* the adapter for implicit adaptation; 
explicitly use it in the place where you need it.