Re: Use of Mac OS X 10.5 / Leopards Garbage Collection Considered Harmful

FROM : Chris Suter
DATE : Thu Feb 07 02:48:22 2008

On 07/02/2008, at 12:06 PM, John Engelhart wrote:

> However, consider for a moment if it was a type attribute, and 
> followed type attribute rules, and how this would effect the 
> examples cited.  Off the top of my head, I think treating it as a 
> type attribute would have prevent every single error I've pointed 
> out.  Hypothetically, consider if UTF8String propagated the __strong 
> type, and the assignment of its pointer to the ivar 'const char *'.
>
> The compiler would fail to compile the code, and generate an error.


I don't think it should be a type qualifier. It would mean that you 
wouldn't be able to do things like:

puts ([myString UTF8String])

without getting a compiler warning.

> Oddly, I had to add a second NSLog() in order to get some kind of 
> lossage, but I think it's fair to chalk this up to the semi-random 
> nature of allocations.


I think that would have been because the pointer returned by 
UTF8String was still on the stack or in a register.

> The above example is now perfectly legal by everyones definition of 
> how things were under retain/release, and I correctly clear the 
> pointer before it goes out of scope, and demonstrates that the GC 
> system can, and does, reclaim live data out from under you.


I think your example is contrived. Whilst it's legal in the retain/
release world you wouldn't ever write anything like that.

The solution to all of this is, as has already been stated, is to 
understand the contract that UTF8String promises and to make your own 
arrangements if you want to hang on to the value.

- Chris