Mailing Lists: Apple Mailing Lists
Image of Mac OS face in stamp
 
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [OT] Retain count riddle

This discussion raises a question I'd like to pose. (I'm relatively new to Cocoa and Objective-C, so apologies if this is a dumb question or one already answered a hundred times.) In this example the macro does not work because [path lastPathComponent] returns a newly created and autoreleased object, so each time it is invoked you get a different object. However, if that method returned a weak reference to an object, such as methods like [mySubView window] do, the macro would have worked fine because the returned object would always be the same one. How do I know which sort of object reference a particular method is going to return? Likewise, in designing my own objects, are there any rules I should follow about this sort of behavior?

Bob S.


On Mar 30, 2004, at 12:23 PM, Christopher Behm wrote:

Well, sub in your arguments to the macro:

[[path lastPathComponent] retain];
[m_Path release];
m_Path = [path lastPathComponent];

If lastPathComponent returns a new object at each call (and it probably does, likely an autoreleased string), then you'd have your problem. Even if it didn't return a new object, it'd be bad practice to do it that way. I'm not macro guru, so I don't know if there's a way to get what you want either.

Chris

On Tuesday, March 30, 2004, at 02:49PM, Sailesh Agrawal <email@hidden> wrote:

So I had this bug the other day that I thought would make an interesting
riddle.

The code looked like this:

#define SAFE_SET(old, new) [new retain]; [old release]; old = new;

...

- (void) foo : (NSString*)path {
SAFE_SET(m_Path, [path lastPathComponent]);
}

Now the problem was any time I accessed m_Path my app would crash. This
isn't cocoa specific, I'm just dumb for using macros where I should have
been using a function. Can anyone guess what the problem is ?

good luck !
Sailesh
_______________________________________________
cocoa-dev mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/cocoa-dev
Do not post admin requests to the list. They will be ignored.
_______________________________________________
cocoa-dev mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/cocoa-dev
Do not post admin requests to the list. They will be ignored.
_______________________________________________
cocoa-dev mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/cocoa-dev
Do not post admin requests to the list. They will be ignored.

References: 
 >Re: [OT] Retain count riddle (From: Christopher Behm <email@hidden>)



Visit the Apple Store online or at retail locations.
1-800-MY-APPLE

Contact Apple | Terms of Use | Privacy Policy

Copyright © 2007 Apple Inc. All rights reserved.