CustomerUniqueCheckerDelegate.swift

class Customer :
            Entity,
            AggregateProtocol
{
    private (set) var id : UUID
    private (set) var email : String
    private var orders : Array<Order>
    
    init?(email : String, name : String, uniqueChecker : CustomerUniqueCheckerDelegate) {
        id = UUID.init()
        self.email = email
        self.orders = Array<Order>()
        super.init(name: name)
        guard uniqueChecker.isUnique(self) else { return nil }
    }
    
	 //...중간생략
}