Delegate

class Array
{
    public delegate void Transformer(ref int item);

    private int[] array;

    public Array(int length)
    {
        Length = length;
        array = new int[Length];
    }

    public int Length { get; set; }

    public int this[int idx]
    {
        get { return array[idx]; }
        set { array[idx] = value; }
    }

    public void Transform(Transformer t)
    {
        for (int i = 0; i < array.Length; ++i)
        {
            t(ref array[i]);
        }
    }
}

class Program
{
    static public void TransformerMethod(ref int item)
    {
        item *= item;
    }

    static void Main(string[] args)
    {
        Array array = new Array(10);

        for (int i = 0; i < array.Length; ++i)
        {
            array[i] = i;
        }

        array.Transform(Program.TransformerMethod);

        for (int i = 0; i < array.Length; ++i)
        {
            Console.WriteLine(array[i]);
        }

        Console.ReadKey();
    }
}