In summary, the existence of fast enumeration does nothing for
existing enumeration technologies and if you have to support
10.4 (as I do) you simply can't use it unless you fork your code.
My solution, in the few cases where performance is paramount,
has been to essentially roll my own fast enumeration. For very
large arrays (thousands of objects) I'll get blocks of objects
in batching using [NSArray getObjects:range:], process those in
a tight C loop, and then get another batch.
The for (in) construct is by far the most optimized general purpose
way to work with any of the collections in Cocoa on 10.5, 10.6, and
iPhone OS. It's also polymorphic, so custom collection subclasses can
fine tune the behavior.
If you have to hand roll your own, either for 10.4, or some
specialized case, your best bet is to use -getObjects: into a local
buffer. gcc supports variable length arrays, and that's the fastest
way to marshall these batches temporarily. You'll want to be very
careful to do length checks to not overrun your stack, and limit the
size. If you have somewhere between 256 & 512 objects, give or take,
you'll have to malloc a temporary id* Overflowing the stack is not
pretty.
- Ben
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