Re: [Pyobjc-dev] Auto bridging instances by conversion

[Just v. R. <ju...@le...>]

bb...@ma... wrote:

> On Tuesday, Feb 4, 2003, at 04:01 US/Eastern, Just van Rossum wrote:
> > Sure, eg. in Python this happens with exceptions. However we're not
> > talking about arbitrary objects, but about real basic immutable
> > types (strings and numbers). I claim that any code in which the id
> > of an NSNumber or NSString is important is seriously broken.
> 
> That claim is faulty.

Uh, I didn't say such code didn't _exist_.

> There are many situations where the type of the object is totally
> irrelevant to the local implementation.  That is, as far as the
> implementation is concerned, everything is an (NSObject*) and the
> only important piece of information is the id-- the self pointer-- of
> that object.    As Ronald indicated, this situation arises outside of
> various random performance hacks-- NSMapTables and the underlying CF*
> types are often used to map instances to other instances, regardless
> of type, as a part of object graph maintenance.

Can't find decent doco for NSMapTable, yet what I have found says it's
not even a true object (it's not even an id); just an opaque struct with
a functional interface. Where are the semantics of NSMapTable _visible_
when using Cocoa classes, and in what case would code actually break if
we supply it with an NSNumber with a different id?

I want things to be as convenient as possible in the usual case, I don't
mind some odd surprises in extreme cases. NSMapTable seems sufficiently
low level that I don't see how it can be relevant to Python code using
Cocoa.

> By assuming otherwise, the bridge will cause very subtle, but very 
> ugly, problems in many situations where the developer is going to be 
> mighty surprised that it didn't "just work".  

I don't believe your "many" qualifier here. A real example would be
useful.

> We already have that 
> situation with the string conversions that are happening now.

Like where? (Apart from the NSMutableString conversion bug of course.)

Just