How to add an optional string extension?

Question

You can create a String extension like so:

extension String {    func someFunc() -> Bool { return true } } 

but what if you want it to apply to optional string?

var optionalString: String? = "" optionalString!.someFunc() /* String? does not have a member someFunc */ 

Attempting to add extension String? { produces the error:

Constrained extension must be declared on the unspecialized generic type 'Optional' with constraints specified by a 'where' clause

Answer 1

In Swift 3.1 you can add an extension to optional values as well:

extension Optional where Wrapped == String {   var isBlank: Bool {     return self?.isBlank ?? true   } } 

Answer 2

You can do it like this:

protocol OptionalType { typealias A; var opt: A? { get } } extension Optional: OptionalType { var opt: A? { return self } }  protocol StringType { var get: String { get } } extension String: StringType { var get: String { return self } }  extension Optional where Wrapped: StringType {   func getOrElse(s: String) -> String {     return self.opt?.get ?? s   } } 

And:

let optStr: String? = nil optStr.getOrElse("hello world") 

The reason that you cannot constrain Optional or String for that matter, is because they are struct. By making pseudo-protocol for each, now we can constrain as we like.

I feel like swift has given up a lot of things just to make it easier for beginners to learn or maybe the language hasn't matured enough yet.