Maybe you have some old code (you wouldn’t write this nowadays, of course) that uses someValue is SomeType checks. Maybe you need to check if someValue is a generic type, like the following Box: Then your is predicates won’t work: The good news is that since you treat the concrete type as a mere marker, you can express this condition with a type marker protocol:
I created a generic CoreDataFetchRequest a while ago and love it. It casts the results to the expected values or throws an error if something went wrong, which it shouldn’t ever, logically – but the Core Data API currently returns AnyObject everywhere, so I have to deal with that.
Swift 2 brings a lot of Cocoa API changes. For one, Core Data’s NSManagedObject’s executeFetchRequest(_:) can throw, returns a non-optional on success, but still returns [AnyObject]. While refactoring existing code to use do-try-catch, I found the optional casting to [MyEntity] cumbersome.
Brent Simmons starts with Swift. And just as I, he struggles with value types, protocols, and generics: once a protocol references another or has a dependency on Self, you cannot use it as a type constraint or placeholder for all descending objects. You either have to use generics to expose a variant for each concrete type, or you re-write the protocol. There’s no equivalent to the way Objective-C did this: something like id<TheProtocol> just doesn’t exist. Swift is stricter. So how do you deal with that?
Objective-C got generics! No more collection classes just for the sake of guarding against invalid elements!
I used custom collection classes a lot for the Word Counter to let the compiler help me prevent mistakes. Swift generics were a godsend for that kind of safety. Now, Objective-C can achieve similar awesomeness.
It can look like this:
@interface Wheel : NSObject
@property (nonatomic, strong) UIColor *color;
@end
@interface Vehicle : NSObject
@property (nonatomic, copy) NSArray<Wheel *> *wheels;
@end
Now the compiler will warn (!) you if you misuse it:
Vehicle *car = [[Vehicle alloc] init];
[car.wheels addObject:@"NSString is of the wrong type"];
Great news, since if you didn’t spend a lot of time creating custom collection types yourself, now at last can you ensure array element type consistency. Makes your code cleaner and more reliable.