Re: Implementing NSFastEnumeration

On Oct 1, 2009, at 6:13 AM, Christiaan Hofman wrote:

> I've been reading the documentation on NSFastEnumeration (both the  
> docs on the protocol and the section in the Objective-C 2.0  
> Programming Language guide). But it is really cryptic and misses  
> most of the relevant information to help in implementing it. The Obj- 
> C 2.0 guide only mentions how to use it. And the NSFastEnumeration  
> doc only has some truly useless descriptions of its rather confusing  
> variables. For instance, saying that state->itemsPtr is "A C array  
> of objects" is about the most useless comment I've ever seen.

I filed a doc bug on that a year and a half ago, asking for an  
implementation example.  It was duped to rdar://problem/4895597.

> And I've also not been able to find any (Apple) sample code that  
> implements this. Perhaps someone can give a link if he has found one?

The documentation was worthless for implementing it.  I used the  
CFArray source as a guide when implementing it for FVPriorityQueue,  
and it was extremely helpful to have a concrete example.

> An important question I have is: which variable should eventually  
> hold the objects to return? As the NSFastEnumeration doc says that  
> stackbuf is "A C array of objects over which the sender is to  
> iterate", which would suggest that that's where the objects should  
> be returned. However I saw this blog at <http://cocoawithlove.com/2008/05/implementing-countbyenumeratingwithstat.html 
> > that has some samples that suggest that the real place to return  
> the objects is in state->itemsPtr. However from the docs I cannot  
> possibly get a clue what that variable is actually used for.

IIRC this depends on whether you can return a pointer to internal  
storage directly, or need to copy them to a temporary C array.

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