How to add an optional string extension?

Question

You can create a String extension like so:

extension String {
   func someFunc -> Bool { ... }
}

but what if you want it to apply to opt

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.

Answer 3

Since Xcode 9.3, you can use this slight modification of @Vladyslav's answer:

extension Optional where Wrapped == String {

    var isEmpty: Bool {
        return self?.isEmpty ?? true
    }

}