How to override method with derived return type in C#?

Question

I want to override a virtual method with a derived class type. What\'s the current best way to do this? So far I\'ve found two approaches:

1. Use an abstract<

Answer 1

The new keyword implicitly 'overrides' the base functionality anyway. Unless for some reason you specifically want override to appear in code, then a single new modifier will suffice. I would also explore abstrating the clone functionality into an interface, it allows you to make more assumptions in code, at a later date.

public interface ICloneable
{
    T Clone();
}

public class A1 : ICloneable
{
    public int X1 { get; set; }
    public A1(int x1) { this.X1 = x1; }

    public virtual A1 Clone()
    {
        return new A1(X1);
    }
}
public class A2 : A1, ICloneable
{
    public int X2 { get; set; }

    public A2(int x1, int x2)
        : base(x1)
    {
        this.X2 = x2;
    }

    public virtual new A2 Clone()
    {
        return new A2(X1, X2);
    }
}

public class A3 : A2, ICloneable
{
    public int X3 { get; set; }

    public A3(int x1, int x2, int x3)
        : base(x1, x2)
    {
        this.X3 = x3;
    }

    public virtual new A3 Clone()
    {
        return new A3(X1, X2, X3);
    }
}

EDIT: The resultant possible behaviour:

public class A4 : A3, ICloneable
{
    public int X4 { get; set; }

    public A4(int x1, int x2, int x3, int x4)
        : base(x1, x2, x3)
    {
        this.X4 = x4;
    }

    public override A3 Clone()
    {
        return ((ICloneable)this).Clone();
    }

    A4 ICloneable.Clone()
    {
        return new A4(X1, X2, X3, X4);
    }
}