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

found some trick swift 3

class A{
    var name:String!;
    init(_ name:String?){
        self.name = name;
    }
}

extension Optional where Wrapped == String {
    func compareText(_ other:String?)->Bool{
        switch (self,other){
        case let(a?,b?):
            return a < b;
        case (nil,_):
            return true;
        default:
            return false;
        }
    }
}

let words:[A] = [A("a"),A(nil),A("b"),A("c"),A(nil)];

// let sorted = words.sorted{ 0.name.compareText($1.name) }
// trick
let sorted = words.sorted{ ($0.name as String?).compareText($1.name) }

print(sorted.map{$0.name});