leaking vs non-leaking singleton

leakingSingleton.m

// LEAKING
@implementation CandidatesWindow
CandidatesWindow *sharedInstance = nil;
- (id)initWithFrame:(CGRect)frame
{
    if (sharedInstance) {
        sharedInstance.frame = frame;
    } else {
        sharedInstance = [super initWithFrame:frame];
    }
    return sharedInstance;
}
@end


// NON-LEAKING
@implementation CandidatesWindow
+(CandidatesWindow *)sharedInstance {
    static dispatch_once_t pred;
    static CandidatesWindow *shared = nil;
    dispatch_once(&pred, ^{
        shared = [[CandidatesWindow alloc] init];
    });
    return shared;
}
@end