title: Suitable key for NSDictionary
body: <p>Is there a way to determine if a class is suitable as a key and will work as you expect, for example I want to use <strong>NSIndexPath</strong> as a key in <strong>NSDictionary</strong> but I don't know for certain if two different <strong>NSIndexPath</strong> instances with the same integer values will always return the same hash value.</p>