Where are the synthesized ivars stored?

Question

I've been reading up on the automatically synthesized ivars. My question is, "WHere are automatically they allocated?" I would have expected them to be part of self, so that I could see them in the debugger, but it seems that the only way I can see them is by invoking the accessor method (via the gdb 'po' command). Isn't there space in the class/object's struct (as there would be for an explicitly declared ivar)?

(Is there a description of the in-memory representation for a modern Objective-C object?)

Being a C guy, it makes me very uncomfortable to not to be able to see where everything is. :-P

Answer 1

Looks like this will tell you: How do automatic @synthesized ivars affect the *real* sizeof(MyClass)?

I am a C guy at heart too. Why bother using these auto generated ones? I like looking at a class and seeing what it holds onto in terms of data.

Interesting: Neat how they took the 64 bit change to make things better. http://www.sealiesoftware.com/blog/archive/2009/01/27/objc_explain_Non-fragile_ivars.html

Answer 2

They are added to the objective-c object (which is a C structure) no different to a regular ivar, so for example:

@interface TestObject : NSObject {

}

@property (nonatomic, assign) int theInt;

@end

@implementation QuartzTestView

@synthesize theInt;

@end

You can refer to theInt ivar directly (not through property accessors) either:

- (void)someMethod {
    theInt = 5;
}

OR

- (void)someOtherMethod {
    self->theInt = 10;
}