C# | Indexers

Difficulty Level : Basic
Last Updated : 25 Nov, 2020

Prerequisite: Properties in C#

An indexer allows an instance of a class or struct to be indexed as an array. If the user will define an indexer for a class, then the class will behave like a virtual array. Array access operator i.e ([ ]) is used to access the instance of the class which uses an indexer. A user can retrieve or set the indexed value without pointing an instance or a type member. Indexers are almost similar to the Properties. The main difference between Indexers and Properties is that the accessors of the Indexers will take parameters.

Syntax:

[access_modifier] [return_type] this [argument_list]
{
  get 
  {
     // get block code
  }
  set 
  {
    // set block code
  }

}

In the above syntax:

access_modifier: It can be public, private, protected or internal.
return_type: It can be any valid C# type.
this: It is the keyword which points to the object of the current class.
argument_list: This specifies the parameter list of the indexer.
get{ } and set { }: These are the accessors.

Example:

C#

// C# program to illustrate the Indexer
using System;
 
// class declaration
class IndexerCreation
{
 
    // class members
    private string[] val = new string[3];
     
    // Indexer declaration
    // public - access modifier
    // string - the return type of the Indexer
      // this - is the keyword having a parameters list
    public string this[int index]
    {
 
        // get Accessor
        // retrieving the values
        // stored in val[] array
        // of strings
        get
        {
 
            return val[index];
        }
 
        // set Accessor
        // setting the value at
        // passed index of val
        set
        {
 
            // value keyword is used
            // to define the value
            // being assigned by the
            // set indexer.
            val[index] = value;
        }
    }
}
 
// Driver Class
class main {
     
    // Main Method
    public static void Main() {
         
        // creating an object of parent class which
        // acts as primary address for using Indexer
        IndexerCreation ic = new IndexerCreation();
 
        // Inserting values in ic[]
        // Here we are using the object
        // of class as an array
        ic[0] = "C";
        ic[1] = "CPP";
        ic[2] = "CSHARP";
 
        Console.Write("Printing values stored in objects used as arrays\n");
         
        // printing values
        Console.WriteLine("First value = {0}", ic[0]);
        Console.WriteLine("Second value = {0}", ic[1]);
        Console.WriteLine("Third value = {0}", ic[2]);
     
    }
}

Output:

Printing values stored in objects used as arrays
First value = C
Second value = CPP
Third value = CSHARP

Important Points About Indexers:

There are two types of Indexers i.e. One Dimensional Indexer & MultiDimensional Indexer. The above discussed is One Dimensional Indexer.
Indexers can be overloaded.
These are different from Properties.
This enables the object to be indexed in a similar way to arrays.
A set accessor will always assign the value while the get accessor will return the value.
“this” keyword is always used to declare an indexer.
To define the value being assigned by the set indexer, ” value” keyword is used.
Indexers are also known as the Smart Arrays or Parameterized Property in C#.
Indexer can’t be a static member as it is an instance member of the class.

My Personal Notes

May	JUN	Jul
	24
2020	2021	2022

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