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Index Struct in C# 8.0

Last Updated : 12 Jul, 2025

Index Struct introduced in C# 8.0. It is used to represent a type that can be used as an index of a collection or sequence that starts from either start or end. It provides a new index style to access elements using the ^ (caret) operator. It is used to find the last elements of the specified collection or sequence. Also with the help of the Index struct, we can create a variable of the index type.

Index-Value: The value property allows us to access the index from the start or the end as an integer by using the Index.Value.
Index with Range: The Index struct can be used with the Range struct to access the range of elements to be sliced from collections.
Read-Only: Its value cannot be modified which helps to make consistency.

Example: In this example, we will see how to access elements of an Array from the end using the Index struct.


 // Accessing elements using Index Struct
using System;

class Geeks
{
	static void Main(string[] args)
	{
		// Creating and initializing an array 
		int[] num = new int[] { 1, 2, 3, 4, 5 };

		// Accessing elements from the start
		Console.WriteLine("Starting Elements");
		Console.WriteLine(num[1]);
		Console.WriteLine(num[2]);
		Console.WriteLine(num[3]);

		// Accessing elements from the end
		Console.WriteLine("Last Elements");
		Console.WriteLine(num[^2]);
		Console.WriteLine(num[^3]);
		Console.WriteLine(num[^4]);
		Console.WriteLine();

		// Index as a variable 
		Index i = ^1;
		Console.WriteLine("Index as a variable: " + num[i]);
	}
}

Output:

Explanation: In the above example, first we access the elements from the start using the traditional way by normal indexes, then we access elements from the end using the Index struct.

Constructor

Index(Int32, Boolean): It is used to initialize a new Index with a specified index position and a value that indicates if the index is from the start or the end of a collection.

Example:


 // C# Program to demonstrate the 
// Constructor of Index Struct
class Geeks
{
    public static void Main()
    {
        // Array
        var arr = new[] { 1, 2, 3, 4, 5, 6, 7, 8 };

        // Index Created using the 
        // Index class constructor
        var i = new Index(2);
        var i2 = new Index(4, true);
        var i3 = new Index(3, false);

       Console.WriteLine( arr[i]); 
       Console.WriteLine( arr[i2]); 
       Console.WriteLine( arr[i3]); 
    }
}

Output:

Properties

Property

Description

End

It is used to get an Index that points beyond the last element.

IsFromEnd

It is used to get a value that indicates whether the index is from the start or the end.

isFromStart

It is used to get an Index that points to the first element of a collection.

Value

It is used to get the index value.

Example:


 // Demonstrating start and end properties 
using System;
class Geeks
{
    public static void Main()
    {
        // Array
        var arr = new[] { 1, 2, 3, 4, 5, 6, 7, 8 };

        // Using Index with Start and End properties
        Index start = 0;
        Index end = ^1;

        // Display Start and End values
        Console.WriteLine("Start Index Value: " + start.Value);
        Console.WriteLine("End Index Value: " + end.Value );

        // Display Elements using Index 
        Console.WriteLine("Element at Start Index: " + arr[start]);
        Console.WriteLine("Element at End Index: " + arr[end]);

        // Check if the index is from the end
        Console.WriteLine("start index from start " 
        + start.IsFromEnd);
        Console.WriteLine("end index from the end: " 
        + end.IsFromEnd);

    }
}

Output:

Methods

Method

Description

Equals()

It is used to check whether the given index is equal to another index or not.

FromEnd(Int32)

It is used to create an Index from the end of a collection at a specified index position.

FromStart(Int32)

It is used to create an Index from the specified index at the start of a collection.

GetHashCode()

It returns the hash code for the given instance.

GetOffset(Int32)

Used to calculate the offset from the start of the collection using the given collection length.

ToString()

It is used to return the string representation of the current Index instance.

Example:


 // Demonstrating Equals method with index
using System;
class Geeks
{
    public static void Main()
    {
        // Array
        var arr = new[] { 1, 2, 3, 4, 5, 6, 7, 8 };

        // Using Index with Start and End properties
        Index start = Index.FromStart(0);
        Index end = Index.FromEnd(1);

        // Access elements using Index
        Console.WriteLine("Value at start index: " + arr[start]);
        Console.WriteLine("Value at end index: " + arr[end]);

        // Check if the start and end are equal
        Console.WriteLine("The start equals to the end: "+
        start.Equals(end));
    }
}

Output:

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