Employee.swift

struct Employee {
    let name: String
    private var _employer: Company
    
    var employer: Company {
        mutating get {
            if !isKnownUniquelyReferenced(&_employer) {
                _employer = _employer.copy() as! Company
            }
            return _employer
        }
        set {
            _employer = newValue
        }
    }
    
    init(name: String, employer: Company = Company()) {
        self.name = name
        self._employer = employer
    }
}