Indexers allow your class to be used just like an array. On the inside of a class, you manage a collection of values any way you want. These objects could be a finite set of class members, another array, or some complex data structure. Regardless of the internal implementation of the class, its data can be obtained consistently through the use of indexers. Here’s an example.
Listing 11-1. An Example of An Indexer: IntIndexer.cs
using System;

///

/// A simple indexer example.
///

class IntIndexer
{
    privatestring[] myData;

   public IntIndexer(int size)
    {
        myData = newstring[size];

        for (int i=0; i < size; i++)
        {
            myData[i] = "empty";
        }
    }

    publicstringthis[int pos]
    {
        get
       {
            return myData[pos];
        }
        set
       {
            myData[pos] = value;
        }
    }

    staticvoid Main(string[] args)
    {
        int size = 10;

        IntIndexer myInd = new IntIndexer(size);

        myInd[9] = "Some Value";
        myInd[3] = "Another Value";
        myInd[5] = "Any Value";

        Console.WriteLine("\nIndexer Output\n");

        for (int i=0; i < size; i++)
        {
            Console.WriteLine("myInd[{0}]: {1}", i, myInd[i]);
        }
    }
}

Listing 11-1 shows how to implement an Indexer. The IntIndexer class has a string array named myData. This is a private array that external users can’t see. This array is initialized in the constructor, which accepts an intsize parameter, instantiates the myData array, and then fills each element with the word “empty”.
The next class member is the Indexer, which is identified by the this keyword and square brackets, this[int pos]. It accepts a single position parameter, pos. As you may have already guessed, the implementation of an Indexer is the same as a Property. It has get and set accessors that are used exactly like those in a Property. This indexer returns a string, as indicated by the string return value in the Indexer declaration.
The Main() method simply instantiates a new IntIndexer object, adds some values, and prints the results. Here’s the output:
Indexer Output

myInd[0]: empty
myInd[1]: empty
myInd[2]: empty
myInd[3]: Another Value
myInd[4]: empty
myInd[5]: Any Value
myInd[6]: empty
myInd[7]: empty
myInd[8]: empty
myInd[9]: Some Value