System/Library/PrivateFrameworks/ContactsFoundation.framework

_CNBlockObservable.h

NSObject
>
CNObservable

@interface _CNBlockObservable : CNObservable {
    id /* block */ _block;
}

- (id)initWithBlock:(id /* block */)a0;
- (id)subscribe:(id)a0;
- (void).cxx_destruct;

@end