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# Indexers

* Indexers enable objects to be indexed in a similar manner to arrays.
* A `get` accessor returns a value. A `set` accessor assigns a value.
* The [this](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/this) keyword is used to define the indexer.
* The [value](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/value) keyword is used to define the value being assigned by the `set` accessor.
* Indexers do not have to be indexed by an integer value; it is up to you how to define the specific look-up mechanism.
* Indexers can be overloaded.
* Indexers can have more than one formal parameter, for example, when accessing a two-dimensional array.

Indexers allow instances of a class or struct to be indexed just like arrays. The indexed value can be set or retrieved without explicitly specifying a type or instance member. Indexers resemble properties except that their accessors take parameters.

{% hint style="info" %}
Indexers are used to index instances of a `class` or `struct`. The indexed values can then be easily accessed like an array, but without explicitly specifying a type or instance member.
{% endhint %}

```csharp
using System;

class SampleCollection<T>
{
   // Declare an array to store the data elements.
   private T[] arr = new T[100];

   // Define the indexer to allow client code to use [] notation.
   public T this[int i]
   {
      get { return arr[i]; }
      set { arr[i] = value; }
   }
   // public T this[int i] => arr[i];
}

class Program
{
   static void Main()
   {
      var stringCollection = new SampleCollection<string>();
      stringCollection[0] = "Hello, World";
      Console.WriteLine(stringCollection[0]);
   }
}
// The example displays the following output:
//       Hello, World.
```