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What is the Real World use of Copy Constructor in C#

Copy constructor technique is not provided by .NET, but we can write one by our-self,

This type of special constructor will take the paramater as object of its type,

If you want create an object for a class with existing object values and only if you want to change some values the copy constructor will come for help

Example:

We have SalesRep class and we want to move all the reptative values in some set of object then we can re-use this,


    class SalesRep
    {
        public int SalesRepID { get; set; }
        public string SalesRepAddress { get; set; }
        public string VisitingDoctor { get; set; }
        public string DoctorAddress { get; set; }
    }


Writing a normal constructor which picks only the doctor details

        public SalesRep(string pVisitingDoctor, string pDoctorAddress)
        {
            VisitingDoctor = pVisitingDoctor;
            DoctorAddress = pDoctorAddress;
        }




SalesRep DrA_Obj = new SalesRep("Doctor A", "Delhi");
SalesRep DrB_Obj = new SalesRep("Doctor B", "Mumbai");
SalesRep DrC_Obj = new SalesRep("Doctor C", "Bangalore");


Then pass the created doctor object into the Copy Constructor to create the complete object with all values, 

Copy Constructor

public SalesRep(SalesRep pSalesRep, int pSalesRepID, string pSalesRepAddress)
{
            SalesRepID = pSalesRepID;
            SalesRepAddress = pSalesRepAddress;
            VisitingDoctor = pSalesRep.VisitingDoctor;
            DoctorAddress = pSalesRep.DoctorAddress;
}


The complete program:




class SalesRep
    {
        public int SalesRepID { get; set; }
        public string SalesRepAddress { get; set; }
        public string VisitingDoctor { get; set; }
        public string DoctorAddress { get; set; }

        public SalesRep(string pVisitingDoctor, string pDoctorAddress)
        {
            VisitingDoctor = pVisitingDoctor;
            DoctorAddress = pDoctorAddress;
        }
        public SalesRep(SalesRep pSalesRep, int pSalesRepID, string pSalesRepAddress)
        {
            SalesRepID = pSalesRepID;
            SalesRepAddress = pSalesRepAddress;
            VisitingDoctor = pSalesRep.VisitingDoctor;
            DoctorAddress = pSalesRep.DoctorAddress;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            SalesRep DrA_Obj = new SalesRep("Doctor A", "Delhi");
            SalesRep DrB_Obj = new SalesRep("Doctor B", "Mumbai");
            SalesRep DrC_Obj = new SalesRep("Doctor C", "Bangalore");

            Dictionary<int, string> SalesRepDetails = new Dictionary<int, string>();
            SalesRepDetails.Add(10001, "Delhi");
            SalesRepDetails.Add(10002, "Mumbai");
            SalesRepDetails.Add(10003, "Delhi");
            SalesRepDetails.Add(10004, "Mumbai");
            SalesRepDetails.Add(10005, "Delhi");
            SalesRepDetails.Add(10006, "Delhi");
            SalesRepDetails.Add(10007, "Bangalore");
            SalesRepDetails.Add(10008, "Delhi");
            SalesRepDetails.Add(10009, "Bangalore");
            SalesRepDetails.Add(10010, "Mumbai");


            List<SalesRep> LstSalesRepObjects = new List<SalesRep>();

            SalesRep SalesRepObj;
            foreach (KeyValuePair<int, string> SingleSalesRepDetails in SalesRepDetails)
            {
                if (SingleSalesRepDetails.Value == "Delhi")
                {
                    SalesRepObj = new SalesRep(DrA_Obj, SingleSalesRepDetails.Key, SingleSalesRepDetails.Value);
                }
                else if (SingleSalesRepDetails.Value == "Mumbai")
                {
                    SalesRepObj = new SalesRep(DrB_Obj, SingleSalesRepDetails.Key, SingleSalesRepDetails.Value);
                }
                else
                //(SingleSalesRepDetails.Value == "Bangalore")
                {
                    SalesRepObj = new SalesRep(DrC_Obj, SingleSalesRepDetails.Key, SingleSalesRepDetails.Value);
                }
                LstSalesRepObjects.Add(SalesRepObj);
            }

            foreach (SalesRep SingleSalesRepObject in LstSalesRepObjects)
            {
                StringBuilder SbMessage = new StringBuilder();
                SbMessage.Append("Sales Rep with ID " + SingleSalesRepObject.SalesRepID + "   ");
                SbMessage.Append("Living in the address " + SingleSalesRepObject.SalesRepAddress + "   ");
                SbMessage.Append("Visiting the doctor " + SingleSalesRepObject.VisitingDoctor + "   ");
                SbMessage.Append("Who is living in " + SingleSalesRepObject.DoctorAddress + "   ");
                Console.WriteLine(SbMessage.ToString());
            }
            Console.ReadLine();
        }
    }
Output:
Sales Rep with ID 10001   Living in the address Delhi   Visiting the doctor Doctor A   Who is living in Delhi

 Sales Rep with ID 10002   Living in the address Mumbai   Visiting the doctor Doctor B   Who is living in Mumbai

 Sales Rep with ID 10003   Living in the address Delhi   Visiting the doctor Doctor A   Who is living in Delhi

 Sales Rep with ID 10004   Living in the address Mumbai   Visiting the doctor Doctor B   Who is living in Mumbai

 Sales Rep with ID 10005   Living in the address Delhi   Visiting the doctor Doctor A   Who is living in Delhi

 Sales Rep with ID 10006   Living in the address Delhi   Visiting the doctor Doctor A   Who is living in Delhi

 Sales Rep with ID 10007   Living in the address Bangalore   Visiting the doctor Doctor C   Who is living in Bangalore   

 Sales Rep with ID 10008   Living in the address Delhi   Visiting the doctor Doctor A   Who is living in Delhi

 Sales Rep with ID 10009   Living in the address Bangalore   Visiting the doctor Doctor C   Who is living in Bangalore   

 Sales Rep with ID 10010   Living in the address Mumbai   Visiting the doctor Doctor B   Who is living in Mumbai




Ideally copy constructors will be used when reusing the existing values in the created objects to create a new object.


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