What is nonnull in objective C?

Question

Can someone elaborate why is nonnull introduced in iOS 9 ?

For example, the NSArray method + (instancetype)array; is now + (

Answer 1

nonnull is keyword which notify compiler that the value returned by object/parameters will never be nil.

In general, you should look at nullable and nonnull roughly the way you currently use assertions or exceptions: violating the contract is a programmer error. In particular, return values are something you control, so you should never return nil for a non-nullable return type unless it is for backwards-compatibility.