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2009-12-01

Tutorial 10:Indexers

C# introduces a new concept known as Indexers which are used for treating an object as an array. The indexers are usually known as smart arrays in C# community. Defining a C# indexer is much like defining properties. We can say that an indexer is a member that enables an object to be indexed in the same way as an array.

this [argument list]
{
get
{
// Get codes goes here
}
set
{
// Set codes goes here
}
}

Where the modifier can be private, public, protected or internal. The return type can be any valid C# types. The 'this' is a special keyword in C# to indicate the object of the current class. The formal-argument-list specifies the parameters of the indexer. The formal parameter list of an indexer corresponds to that of a method, except that at least one parameter must be specified, and that the ref and out parameter modifiers are not permitted. Remember that indexers in C# must have at least one parameter. Other wise the compiler will generate a compilation error.
The following program shows a C# indexer in action

// C#: INDEXER

using System;
using System.Collections;

class MyClass
{
private string []data = new string[5];
public string this [int index]
{
get
{
return data[index];
}
set
{
data[index] = value;
}
}
}


class MyClient
{
public static void Main()
{
MyClass mc = new MyClass();
mc[0] = "Rajesh";
mc[1] = "A3-126";
mc[2] = "Snehadara";
mc[3] = "Irla";
mc[4] = "Mumbai";
Console.WriteLine("{0},{1},{2},{3},{4}",mc[0],mc[1],mc[2],mc[3],mc[4]);
}
}

The indexers in C# can be overloaded just like member functions. The formal parameter list of an indexer defines the signature of the indexer. Specifically, the signature of an indexer consists of the number and types of its formal parameters. The element type is not part of an indexer's signature, nor is the names of the formal parameters. The signature of an indexer must differ from the signatures of all other indexers declared in the same class. C# do not have the concept of static indexers. If we declare an indexer static, the compiler will show a compilation time error.

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