using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}

    public abstract class BasePoly

    {

        public abstract double X { get; set; }

        public abstract double Y { get; set; }

        public abstract double Width { get; set; }

        public abstract double Height { get; set; }

    }

    public abstract class BasePoly<T> : BasePoly

    {

        public T poly { get; private set; }

        protected BasePoly(T poly) { this.poly = poly; }

    }

    public class PolyLineAdapter : BasePoly<PolyLine>

    {

        public PolyLineAdapter(PolyLine poly) : base(poly) {}

        // override abstracts and forward to inner PolyLine instance at 'this.poly'

        public override double X { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

        public override double Y { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

        public override double Width { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

        public override double Height { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

    }

    public class FaceAdapter : BasePoly<Face>

    {

        public FaceAdapter(Face poly) : base(poly) {}

        // override abstracts and forward to inner Face instance at 'this.poly'

        public override double X { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

        public override double Y { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

        public override double Width { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

        public override double Height { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

    }

    interface IEntity

    {

        BasePoly GetPoly();

        void   InsertPoly(BasePoly poly);

    }

    public abstract class Entity<TEntity> : IEntity

        where TEntity : BasePoly

    {

        public BasePoly GetPoly()

        {

            return this.GetExternalPoly();

        }

        public abstract TEntity GetExternalPoly();

        public void InsertPoly(BasePoly poly)

        {

            this.InsertExternalPoly((TEntity) poly);

        }

        public abstract void InsertExternalPoly(TEntity poly);

    }

    public class AutocadEntity : Entity<PolyLineAdapter>

    {

        public override PolyLineAdapter GetExternalPoly()

        {

            throw new NotImplementedException();

        }

        public override void InsertExternalPoly(PolyLineAdapter poly)

        {

            throw new NotImplementedException();

        }

    }

    public class SketchupEntity : Entity<FaceAdapter>

    {

        public override FaceAdapter GetExternalPoly()

        {

            throw new NotImplementedException();

        }

        public override void InsertExternalPoly(FaceAdapter poly)

        {

            throw new NotImplementedException();

        }

​

    }

    // fills for third party classes

    public class PolyLine {}

    public class Face {}