Why C# doesn't allow inheritance of return type when implementing an Interface

Question

Is there any rational reason why the code below is not legal in C#?

class X: IA, IB
{
    public X test() // Compliation Error, saying that X is not IB
    {         


        

Answer 1

This can help http://geekswithblogs.net/abhijeetp/archive/2010/01/10/covariance-and-contravariance-in-c-4.0.aspx You can use the "out" keyword