On 12 Jun '08, at 10:41 AM, Andy Lee wrote:
I hadn't thought of this case.Thanks for the pointer to the docs -- I now see there is a vulnerability in the accessors I've been writing.
This is kind of a religious issue. Some people like the safer accessors. Some people see them as a very expensive* workaround for a problem that rarely occurs.
I'm firmly in the latter camp. I've never used this 'safe' form of accessor, and have only rarely run into the kind of crash it prevents; and it was always pretty easy to track down and fix. (The fix is just for the caller to retain the value it got from the accessor, then release it when it's done using it.)
Another alternative is to leave the getters simple, but change the _setter_ methods to autorelease the old value instead of releasing it; that prevents this same crash, but is less expensive because setters are much more rarely called than getters (and -autorelease isn't much more expensive than -release.)
—Jens* A basic accessor requires one or two machine instructions to do the actual work; whereas -retain and -autorelease involve extra method dispatches that each acquire a global lock and do a hashtable lookup. Obviously any one call isn't going to take a noticeable amount of time, but accessor calls are so damn ubiquitous that this can have an overall impact on app performance in some cases. Not to mention memory usage, since autoreleased objects have a longer lifespan and can build up during loops.
smime.p7s
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