Pointer is missing a nullability type specifier

Question

In Xcode 7 GM I started to get this warning:

Pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)

In the following function declaration (NSUserDefaults extension)

- (void)setObject:(nullable id)value
           forKey:(NSString *)defaultName
    objectChanged:(void(^)(NSUserDefaults *userDefaults, id value))changeHandler
    objectRamains:(void(^)(NSUserDefaults *userDefaults, id value))remainHandler;

Why this warning is showing and how should I fix it?

Answer 1

You can use the following macros around blocks of declarations (functions and variables) in objective c headers:

NS_ASSUME_NONNULL_BEGIN 

NS_ASSUME_NONNULL_END

You need to then add nullable annotations for references that can be nil within that block. This applies to both function parameters and variable declarations.

As in:

@interface SMLBaseUserDetailsVC : UIViewController < UICollectionViewDelegate>
NS_ASSUME_NONNULL_BEGIN

@property (nonatomic, readonly) IBOutlet UIScrollView *detailsScrollView;
@property (nonatomic, readonly) IBOutlet UICollectionView *photoCV;
@property (nonatomic, weak, readonly) SMLUser *user;
- (IBAction)flagUser:(id)sender;
- (IBAction)closeAction:(nullable id)sender;
- (void) prefetchPhotos;

NS_ASSUME_NONNULL_END

@end

Edit* The why??? is because for an objective-c class to be interoperable with swift, you need to declare nullability so that the compiler knows to treat properties as swift optionals or not. Nullable objective c properties are known as optionals in swift and using these macros in conjunction with the nullable declarators for properties allows the compiler to treat them as optionals (Optionals are monads - an object that wraps up either the object or nil).