I'm writing a tool which would benefit from knowing which of a class' instance variables are declared __weak
.
This information must exist somewhere at runtime, but is there any way of accessing it, documented or otherwise? (It's for a tool, so I don't care so much about it breaking with updates)
Alright, here is a sample implementation, using a custom object implementation, that does a rudimentary check to see if an iVar is weak or not:
BOOL iVarIsWeak(Class cls, Ivar ivar)
{
id classInstance = [cls new];
// our custom base class properly tracks reference counting, no weird voodoo
id refCounter = [CustomBaseClass new];
object_setIvar(classInstance, ivar, refCounter);
if ([refCounter refCount] == 2)
{
return NO;
}
return YES;
}
The above code is meant to be used with ARC enabled, while the following custom object code is not:
@interface CustomBaseClass : NSObject
+(id) new;
+(id) alloc;
-(id) init;
-(id) retain;
-(void) release;
-(id) autorelease;
-(void) dealloc;
-(id) description;
-(unsigned) refCount;
@end
// easy way to get sizeof
struct CustomBaseClassAsStruct {
voidPtr isa;
unsigned volatile refcount;
};
@implementation CustomBaseClass
{
unsigned volatile refcount;
}
+(id) new
{
return [[self alloc] init];
}
+(id) alloc
{
struct CustomBaseClassAsStruct *results = malloc(sizeof(struct CustomBaseClassAsStruct));
results->isa = self;
results->refcount = 0;
return (id) results;
}
-(id) init
{
[self retain];
return self;
}
-(id) retain
{
++refcount;
return self;
}
-(void) release
{
if (--refcount == 0)
[self dealloc];
}
-(id) autorelease
{
// sample implementation of autorelease
dispatch_async(dispatch_get_current_queue(), ^{
[self release];
});
return self;
}
-(unsigned) refCount
{
return refcount;
}
-(void) dealloc
{
free(self);
// no call to [super dealloc], we are using custom memory-managment
}
@end
This ONLY works for weak iVars. With a unsafe_unretained
variable, it will give a false positive, my best guess for this is because __weak
information is saved at runtime whilst unsafe_unretained
information is not.
I hope this helps!
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