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indexers :: Advance : C# programming for c++ programmers

1. Where are indexers used in .NET :

To store or retrieve data from session state or application state variables, we make use indexers.

 Session["sessiondata"] = "sessiondata";


2. Defination :
An indexer allows an object to be indexed such as an array

Syntax :

 A one or multi param indexer has the following syntax:

element-type this[int index, ..]
{
   // The get accessor.
   get
   {
      // return the value specified by index
   }
   
   // The set accessor.
   set
   {
      // set the value specified by index
   }
}



Points to remember:
1. We then created an indexer using "this" keyword. This indexer takes employeeId as parameter and returns employee name.
public string this[int employeeId]
2. Just like properties indexers have get and set accessors.
3. Indexers can also be overloaded. 


using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

 namespace Demo
{
    public class Employee
    {
        public int EmpId { get; set; }
        public string Name { get; set; }
    }

     public class Orgnization
    {
        private List lEmployees;

         public Orgnization()
        {
            lEmployees = new List();

             lEmployees.Add(new Employee { EmpId = 101, Name = "iliyas"});
            lEmployees.Add(new Employee { EmpId = 102, Name = "patel"});
            lEmployees.Add(new Employee { EmpId = 103, Name = "kabir"});
            
        }

         
        public string this[int empId]
        {
            
            get
            {
                return lEmployees.FirstOrDefault(emp => emp.EmpId  == empId).Name;
            }
            set
            {
                lEmployees.FirstOrDefault(emp => emp.EmpId  == empId).Name = value;
            }
        }
    }
}




Using indexer:

Orgnization org = new Orgnization();
console.writeline(org[0]);
console.writeline(org[1]);
console.writeline(org[2]);
org[2] = "Name of employee updated here ";



3. Overloaded Indexers :
Indexers can be overloaded.

Example:

namespace Demo
{
    public class Employee
    {
        public int EmpId { get; set; }
        public string Name { get; set; }
public string Salarycode { get; set; }
    }

     public class Orgnization
    {
        private List lEmployees;

         public Orgnization()
        {
            lEmployees = new List();

             lEmployees.Add(new Employee { EmpId = 101, Name = "iliyas", Salarycode = "MP012"});
            lEmployees.Add(new Employee { EmpId = 102, Name = "patel" , Salarycode = "MP032"});
            lEmployees.Add(new Employee { EmpId = 103, Name = "kabir" , Salarycode = "MP022"});
            
        }

         
        public string this[string SaCode]
        {
            
            get
            {
                return lEmployees.FirstOrDefault(emp => emp.Salarycode  == SaCode).Name;
            }
            set
            {
                lEmployees.FirstOrDefault(emp => emp.Salarycode  == SaCode).Name = value;
            }
        }
    }
}

Using indexer:

Orgnization org = new Orgnization();
console.writeline(org["MP012"]);
console.writeline(org["MP032"]);
console.writeline(org["MP022"]);
org[2] = "sal updated here ";

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