NSError polymorphism approach example

ClientCode.mm

#import <NSError+UserFriendly.h>


-(void)onMyNewsLoadingCompleted:(id)maybeResult
error:(NSError*)maybeError
{
    [error presentAlertToTheUser];
}

NSError+UserFriendly.h

@interface NSError( UserFriendly)

-(void)presentAlertToTheUser;

@end

XYLoadMyNewsError+UserFriendly.h

@interface XYLoadMyNewsError(UserFriendly)

-(void)presentAlertToTheUser;

@end

XYLoadMyNewsError.h

@interface XYLoadMyNewsError : NSError
@end

-(void) presentAlertToTheUser
{
   // Please avoid using UIAlertController directly
   [ [XYZErrorPrezenter instance] presentMyNewsError: self]
}