Re: Objective-C and Smalltalk; speed of message send

[Marcel Weiher]

Hi Travis!

> Do real world examples count then?

Always!

> For a while we've considered porting a straight C processing 
> application upward into Objective-C. One of the things we wanted to do 
> was use a Dictionary (NSMutableDictionary) to store arbitrarily keyed 
> tallies. This would replace an existing 2D array in strict C.

Whoa, an NSDictionary is a pretty heavy-weight item, especially 
compared to a simple 2D array!  Why not stick with the 2D array, if I 
may ask?  After all, one of the point of Objective-C is that it *is* C.

>  We decided to use NSStrings as the keys.

Also potentially fairly heavy, though a common choice.  I remember 
people complaining about NSString's performance compared to char* when 
Foundation was introduced.  However, NSString is really for "human 
readable" text, whereas char* is often more for "tokens", or really 
just byte-sequences.

>  To maintain a backwards bridge, we took the old 2D access indices and 
> turned them into a string. And then stored/set them in the 
> NSMutableDictionary via those. The performance was not impressive.

I wouldn't expect it to be.  NS(Mutable)Dictionary is pretty slow.  One 
issue is that it copies its keys.  Arrrggghh.

>  I got some pointers from this mailing list, which improved things.

What were the suggestions?

>  In the end, we'd squeezed out a solution which was almost 50% of the 
> speed what VisualWorks Smalltalk did the same task in. The Smalltalk 
> one was still 2x faster though, i never had to think about the memory 
> management issues, and it worked the first time.

No complaints about Smalltalk from me :-))

> That aside, I'm still a huge Objective-C fan, and we may still go that 
> route anyway. We're not sure how to get our semi-realtime data 
> into/outof the Smalltalk memory model fast enough. :)

Yep, the really great thing about Objective-C is its connectivity.

Cheers,

Marcel


--
Marcel Weiher                           Metaobject Software Technologies
marcel@metaobject.com           www.metaobject.com
Metaprogramming for the Graphic Arts.   HOM, IDEAs, MetaAd etc.
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