Indexers in .NET

Defining an indexer allows you to create classes that act like "virtual arrays." Instances of that class can be accessed using the [] array access operator. Defining an indexer in C# is similar to defining operator [] in C++, but is considerably more flexible. For classes that encapsulate array- or collection-like functionality, using an indexer allows the users of that class to use the array syntax to access the class.

Example

The following example shows how to declare a private array field, myArray, and an indexer. Using the indexer allows direct access to the instance b[i]. The alternative to using the indexer is to declare the array as a public member and access its members, myArray[i], directly.

// cs_keyword_indexers.cs
using System;
class IndexerClass
{
private int [] myArray = new int[100];
public int this [int index] // Indexer declaration
{
get
{
// Check the index limits.
if (index < 0 || index >= 100)
return 0;
else
return myArray[index];
}
set
{
if (!(index < 0 || index >= 100))
myArray[index] = value;
}
}
}

public class MainClass
{
public static void Main()
{
IndexerClass b = new IndexerClass();
// Call the indexer to initialize the elements #3 and #5.
b[3] = 256;
b[5] = 1024;
for (int i=0; i<=10; i++)
{
Console.WriteLine("Element #{0} = {1}", i, b[i]);
}
}
}