enum Fruit     { case apple }
enum Vegetable { case broccoli }
enum Meat      { case chicken }


protocol EatsFruit      { }
protocol EatsVegetables { }
protocol EatsMeat       { }


struct Chef <Client> { }


extension Chef where Client: EatsFruit {
    func cook (_ food: Fruit) { }
}
extension Chef where Client: EatsVegetables {
    func cook (_ food: Vegetable) { }
}
extension Chef where Client: EatsMeat {
    func cook (_ food: Meat) { }
}


struct Vegetarian: EatsFruit, EatsVegetables { }




func demo () {
    let gordon = Chef<Vegetarian>()
    // gordon.cook()

    // Uncomment the line above and type a `.` in between the parentheses of cook(). My Xcode version is Version 10.2 beta (10P82s) and autocomplete shows me "apple", "broccoli" and "chicken" when it should only show me "apple" and "broccoli". 
}