Objective-C APIs can now express the “nullability” of parameters, return types, properties, variables, etc. For example, here is the expression of nullability for several UITableView APIs:
-(void)registerNib:(nonnull UINib *)nib forCellReuseIdentifier:(nonnull NSString *)identifier;
-(nullable UITableViewCell *)cellForRowAtIndexPath:(nonnull NSIndexPath)indexPath;
@property (nonatomic, readwrite, retain, nullable) UIView *backgroundView;The nullability qualifiers affect the optionality of the Objective-C APIs when in Swift. Instead of being imported as implicitly-unwrapped optionals (e.g., UINib!), nonnull-qualified types are imported as non-optional (e.g., UINib) and nullable-qualified types are imported as optional (e.g., UITableViewCell?), so the above APIs will be seen in Swift as:
func registerNib(nib: UINib, forCellReuseIdentifier identifier: String)
