protocol_hashable.swift

func unique<S: Sequence, E: Hashable>(_ source: S) -> [E] where E==S.Iterator.Element {
    var seen: [E:Bool] = [:]
    return source.filter { seen.updateValue(true, forKey: $0) == nil }
}

let a = ["four","one", "two", "one", "three","four", "four"]
print(unique(a))

struct Person {
    var name: String
    var age: Int
}

extension Person: Hashable {
    var hashValue: Int {
        get {
            return name.hashValue ^ age.hashValue
        }
    }
    
    static func ==(l: Person, r: Person) -> Bool {
        return l.hashValue == r.hashValue
    }
}



let p = [Person(name: "Jack", age: 22),
         Person(name: "Anne", age: 26),
         Person(name: "Mary", age: 27),
         Person(name: "Anne", age: 26)]
print(unique(p))

p.contains(Person(name: "Bruno", age: 22))