class TypeHandle {};

​

class Constant 

{

    public void Initialize(TypeHandle constantTypeHandle) {}

}

​

interface IStencil 

{

    Constant CreateConstantValue(TypeHandle constantTypeHandle);

}

​

class GraphModel : IStencil

{

    public IStencil Stencil { get; set; } = null;

    public virtual Constant CreateConstantValue(TypeHandle constantTypeHandle)

    {

        if (Stencil != null)

            return Stencil.CreateConstantValue(constantTypeHandle);

        var instance = new Constant();

        instance.Initialize(constantTypeHandle);

        return instance;

    }

    public virtual int SomeOtherAPI() => 0;

}

​

/*** Now a tool needs to derive from GraphModel. */

​

class ToolGraphModel : GraphModel

{

    /* Should I override CreateConstantValue, or should I set a stencil? */

    public override int SomeOtherAPI() => 1;

}