Invalid Type Cast Objective C

invalidCast.m

// Suppose `urls` is an property of a class of type NSArray and it contains NSURLs
NSString *string = self.urls[0];
NSString *firstCharacter = [string subtringToIndex:1];

// This would break at runtime because we casted it to the wrong value type.
// We can get around this by creating NSArrays that are generic over NSURL. That way we would get a warning on the NSString cast.
// I may also mention that NSArrays can store objects of different types unlike Swift where all the object must be of the same type.
// That said, objects that contain multiple types that do not all inherit from the same object or conform to the same protocol usually should never be in the same NSArray