Swift instance variable with protocol

Question

I have to translate the following lines of Objective-c code into swift. This is a sample from the Objective-c JSONModel-Framework where the Optional protocol provided by the Framework is applied to an instance variable of type NSString. I found a related post but i didn't managed to achieve it. With my MYModel.swift implementation Xcode complains Cannot specialize non-generic type NSString

thx for your help!

MYModel.swift

@objc(MYModel) public class MYModel : JSONModel {
   ...
   public var name : NSString<Optional>
   ...
}

MYModel.h

@interface MYModel : JSONModel
...
@property (strong, nonatomic) NSString<Optional>* name; 
...

JSONModel.h

...
/**
 * Protocol for defining optional properties in a JSON Model class. Use like below to define 
 * model properties that are not required to have values in the JSON input:
 * 
 * @property (strong, nonatomic) NSString<Optional>* propertyName;
 *
 */
@protocol Optional
@end
...

Answer 1

The < and > are not for conforms to protocol. It is for Types with generics like Array:

Array<T>

so you can write var a: Array<String>.

You want something else, a variable should be a Type String and conform to the protocol

---

You can extend String with the protocol and add the needed functions yourself.

Since your Optional protocol is empty, it is enough to write:

extension NSString: Optional {} // you can use String if you like

To create the protocol write in Swift:

protocol Optional {}

You can Objective-C create the protocol, too.

---

You should not use Optional, because there is already one, but because Swift has namespacing, it works. You could of course write something like that:

extension NSString: JsonOptProtocol {}

protocol JsonOptProtocol {} // or create that in Objective-C like you did

---

Documentation link.