Re: [Pyobjc-dev] Calling methods on nil

[Marcel W. <ma...@me...>]

On Sunday, May 11, 2003, at 11:34  Uhr, Just van Rossum wrote:

> Marcel Weiher wrote:
>
>>> The mechanics differ, but it's the same thing (OO with dynamic
>>> method dispatching).
>>
>> Exactly.  There is dynamic dispatch.  So when you "send a message",
>> you get dynamic dispatch, and THEN the method is called.  If you just
>> say "the method is called", you are simply *verbally* omitting the
>> dynamic dispatch, though of course it is still happening.
>
> That's just a matter of perspective <wink>: to me "the method foo of
> this object" means the method you'd get when dispatching.

Yes.  This means that you have *implied* a dispatching mechanism when 
you speak of "the method foo of this object".  (You didn't mention it 
explicitly, but it is there -> implied).

What about this is difficult?

> Since dynamic
> method dispatching is so deeply integrated in Python, I don't see how 
> it
> could mean anything else, so I disagree I'm omitting something crucial.

I am not saying that you are "omitting" anything.  I am saying you are 
not mentioning *explicitly*, but *implicitly*.  This behavior is 
implied by what you are saying.

> I'm not arguing against sending messages to nil in ObjC (although I
> don't like it, see below), but against supporting it by PyObjC in
> *Python*.

I have no problem with handling it one way or the other.  I had a 
problem with the 'reasoning' you presented, which was quite wrong.

> (Just yesterday I was working on some code where a (Cocoa) method
> unexpectedly returned nil (translated to None in Python). I was
> extremely happy to get a traceback instead of silent failure; since 
> None
> is an actual object, it dispatches methods just like most other 
> objects,
> ie. raise an exception if a method isn't found. A silent failure surely
> would've cost me much more time to figure out what I did wrong. 
> Ignoring
> messages to nil is convenient when you expect it, but it's a liability
> when you don't. I much rather explicitly test for nil than shoot myself
> in the foot.)

Well, I am just as happy that I don't have to obscure my code with 
clutter...

So there we are, two happy people ;-)

Marcel

-- 
Marcel Weiher				Metaobject Software Technologies
ma...@me...		www.metaobject.com
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