@interface MyClass ()

@property (readwrite, strong) CFMutableSetRef __attribute__((NSObject)) completeContents;

@end

Boolean APIObjectEqual (const void *value1, const void *value2);

Boolean APIObjectEqual (const void *value1, const void *value2)
{
    return [(__bridge_transfer OSPAPIObject *)value1 isEqualToAPIObject:(__bridge_transfer OSPAPIObject *)value2];
}

@implementation MyClass

@synthesize completeContents;

- (id)init
{
    self = [super init];

    if (nil != self)
    {
        CFSetCallBacks callbacks = kCFTypeSetCallBacks;
        callbacks.equal = APIObjectEqual;
        [self setCompleteContents:CFSetCreateMutable(NULL, 0, &callbacks)];
    }

    return self;
}

- (void)addObject:(OSPAPIObject *)apiObject
{
    CFSetAddValue([self completeContents], (__bridge_retained const void *)apiObject);
}

@end