How to take a diff of app contacts against phoneBook?
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I have a contact book on my application and need to sync those contacts with server cum phonebook regularly. 

Rather taking total phoneBook to update app's contacts, I am thinking of diff of changed contacts for which I didn't find a functionality in `ABAddessBook` API. Problem is that the contact objects in the app are of different type to contact objects that I get from phoneBook
via function `ABAddressBookCopyArrayOfAllPeople()`.

If I get difference of changed contacts efficiently, then I can just sync those contacts only.
Will that be possible?

Thanks.