protocol Drinkable {

    associatedtype PrimaryIngredient: Ingredient
    associatedtype SecondaryIngredient: Ingredient

    var ingredients: [Any] { get set }

    mutating func fill()

    /**
     Provides the secondary ingredient

     - returns: The secondary ingredient
     */
    func provideMilk() -> SecondaryIngredient

    /**
     Provides the primary ingredient which will be mostly some sort of coffee

     - returns: The primary ingredient
     */
    func provideCoffee() -> PrimaryIngredient
}