What does it mean to create an object using: id <class> instanceName?

Question

I saw some code on the apple website that goes like this

id <NSFetchedResultsSectionInfo> sectionInfo = ...

How is this different to the following?

NSFetchedResultsSectionInfo *sectionInfo = ...

I'm not so interested in NSFetchedResultsSectionInfo itself, but rather the way it's declared.

Thanks a bunch!
Tristan

Answer 1

NSFetchedResultsSectionInfo is a protocol. id is a way of declaring a generic object, and id <NSFetchedResultsSectionInfo> declares a generic object that must adhere to the NSFetchedResultsSectionInfo protocol.