Cyrus just can’t stop!  First he Refactored Optional<>, basically to use a singleton for None<>

 

interface IOptional<A>

{

    A Value { get; }

}

class None<A> : IOptional<A>

{

    public static readonly IOptional<A> Instance = new None<A>();

 

    private None() { }

 

    A IOptional<A>.Value

    {

        get { throw new InvalidOperationException(); }

    }

}

class Some<A> : IOptional<A>

{

    readonly A value;

 

    public Some(A value)

    {

        this.value = value;

    }

 

    A IOptional<A>.Value

    {

        get

        {

            return value;

        }

    }

}

 

He kept getting annoyed with himself for having an interface with only one method (IOptional), as that’s a smell that you need a delegate.  I insisted that an interface is the right thing, because a delegate isn’t just a single-method interface – it also is just about “shape”.  That is, a method with the right signature can satisfy a matching delegate, but you can’t satisfy an interface with a class unless you actually inherit from that interface.

 

To put it another way: methods don’t inherit from delegates.

 

Or yet another: inheritance counts from something.

 

He finally agreed and let it be.