C# : Indexes in Classes

Indexes are generally used to access a specific element or setting a value to a specific element in a collection or a array. But indexes can be used on classes/structs or interfaces to provide an array like access. Let’s consider the following Fruit class.

public class Fruit

{

    public Fruit(int length)

    {

        this.items = new string[length];

    }

    private string[] items;

    public string[] Items

    {

        get { return items; }

        set { items = value; }

    }

}

It’s pretty simple class, I have an array of type string and in the constructor I am initializing the array with a given length. So this is how I would access the Items array from outside.

static void Main(string[] args)

{

    Fruit fruits = new Fruit(10);

    fruits.Items[0] = "Apple";

    fruits.Items[1] = "Orange";

}

Now if we can omit the part where we are accessing Items array through fruits.Items and can access it like fruits[0], fruits[1] etc. isn’t that great. And that’s where the Indexes can be real handy. And here is how we can define an Index in the Fruit class.

public class Fruit

{

    private string[] items;

    public Fruit(int length)

    {

        this.items = new string[length];

    }

    public string this[int index]

    {

        get { return items[index]; }

        set { items[index] = value; }

    }

    public int Length

    {

        get

        {

            return items.Length;

        }

    }

}

Here I have a private string array and in the constructor I am initializing the array with a given length. I have another property which exposes the length of the array. And then I have the Index syntax.

Now let’s see how we can access items array through the Index defined for the class.

Fruit fruits = new Fruit(5);

fruits[0] = "Apple";

fruits[1] = "Orange";

for (int i = 0; i < fruits.Length; i++)

{

    Console.WriteLine(fruits[i]);

}

Result

Isn’t that great.

Happy Coding.

Regards,
Jaliya