using System;   

​

static class ArrayExtensions

{

    public static int IndexOf<T>(this T[] array, T value)

    {

        return Array.IndexOf(array, value);

    }   

}

​

public class Program

{

    public static void Main()

    {

        // Usage

        int[] array = { 9,8,7,6,5 };

​

        var index = array.IndexOf(7);

​

        Console.WriteLine(index); // Prints "2"

    }

}

​

​