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Ravi Vishwakarma
Ravi Vishwakarma

IT-Hardware & Networking

Ravi Vishwakarma is a dedicated Software Developer with a passion for crafting efficient and innovative solutions. With a keen eye for detail and years of experience, he excels in developing robust software systems that meet client needs. His expertise spans across multiple programming languages and technologies, making him a valuable asset in any software development project.

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1 Answers

Anubhav Sharma
Anubhav Sharma 30 May 2026
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In C#, indexers allow an object to be accessed like an array by using square brackets ([]). They provide a way to define how values are retrieved or assigned using an index.

Why Use Indexers?

Without an indexer:

public class StudentCollection
{
    private string[] students = new string[5];

    public string GetStudent(int index)
    {
        return students[index];
    }

    public void SetStudent(int index, string value)
    {
        students[index] = value;
    }
}

Usage:

StudentCollection collection = new StudentCollection();

collection.SetStudent(0, "John");
Console.WriteLine(collection.GetStudent(0));

With an indexer, the syntax becomes much cleaner.

Basic Indexer Syntax

public class StudentCollection
{
    private string[] students = new string[5];

    public string this[int index]
    {
        get
        {
            return students[index];
        }
        set
        {
            students[index] = value;
        }
    }
}

Usage:

StudentCollection collection = new StudentCollection();

collection[0] = "John";
collection[1] = "Alice";

Console.WriteLine(collection[0]);
Console.WriteLine(collection[1]);

Output:

John
Alice

How It Works

The keyword this defines an indexer:

public string this[int index]
  • get is executed when reading a value.
  • set is executed when assigning a value.
  • value represents the assigned value inside the setter.

Example:

collection[0] = "John";

Internally calls:

set
{
    students[0] = "John";
}

Indexers with Multiple Parameters

Indexers can accept multiple parameters.

public class Matrix
{
    private int[,] data = new int[3, 3];

    public int this[int row, int column]
    {
        get
        {
            return data[row, column];
        }
        set
        {
            data[row, column] = value;
        }
    }
}

Usage:

Matrix matrix = new Matrix();

matrix[1, 2] = 100;

Console.WriteLine(matrix[1, 2]);

Output:

100

String-Based Indexers

Indexers don't have to use integers.

public class EmployeeDirectory
{
    private Dictionary<string, string> employees =
        new Dictionary<string, string>();

    public string this[string employeeId]
    {
        get
        {
            return employees[employeeId];
        }
        set
        {
            employees[employeeId] = value;
        }
    }
}

Usage:

EmployeeDirectory directory = new EmployeeDirectory();

directory["E001"] = "John";
directory["E002"] = "Alice";

Console.WriteLine(directory["E001"]);

Output:

John

Read-Only Indexer

If you only need retrieval:

public class Numbers
{
    private int[] data = { 10, 20, 30 };

    public int this[int index]
    {
        get
        {
            return data[index];
        }
    }
}

Usage:

Numbers numbers = new Numbers();

Console.WriteLine(numbers[1]);

Output:

20

Write-Only Indexer

Although uncommon, you can create a write-only indexer:

public class Logger
{
    public string this[int index]
    {
        set
        {
            Console.WriteLine($"Value: {value}");
        }
    }
}

Real-World Examples

Indexers are commonly used in:

  • Custom collections
  • Caching systems
  • Data containers
  • Grid or matrix implementations
  • Wrappers around dictionaries
  • Configuration managers

Examples in .NET:

List<T>

Dictionary<TKey, TValue>

DataRow

List<string> names = new List<string>();

names.Add("John");

Console.WriteLine(names[0]);

List<T> uses an indexer internally.

Indexer vs Property

Property Indexer
Accessed by name Accessed by index
obj.Name obj[0]
Represents a single value Represents a collection-like structure
Uses property name Uses this keyword

Example:

person.Name = "John";

vs

students[0] = "John";

Interview Question

Can a class have multiple indexers?

Yes, as long as their parameter signatures are different.

public class DataStore
{
    public string this[int index]
    {
        get { return "Integer Index"; }
    }

    public string this[string key]
    {
        get { return "String Key"; }
    }
}

Usage:

DataStore store = new DataStore();

Console.WriteLine(store[1]);
Console.WriteLine(store["A"]);

Output:

Integer Index
String Key

Summary

An indexer is a special class member that lets objects be accessed using array-like syntax (obj[index]). It is declared using the this keyword and can have get, set, or both accessors. Indexers are particularly useful when building custom collections or data structures that should feel natural to use, similar to arrays, lists, and dictionaries.

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