Nullability Annotations

Two groups of nullability annotations -_Nullable/_Nonnull and nullable/nonnull. The lowercase one is more elegant and works for almost all scenarios:

• Method declarations - write the annotation right after the open parenthesis of the parameter

  • - (nullable NSString *) getItemWithIdentifier:(nonnull NSString*)identifier;

• Property declarations - write the annotation in the attributes list

  • @property (copy, nonnull) NSString* name;

• You can also define Nullability regions to mark specific regions in the file to consider any pointer type to be nonnull. So you need to explicitly mark only nullable properties/parameters

  • NS_ASSUME_NONNULL_BEGIN and NS_ASSUME_NONNULL_END

Source: https://developer.apple.com/swift/blog/?id=25