MixinWithInterfacesAndExtensionMethods.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    // Version C# to: https://gist.github.com/adomokos/989193

    public abstract class CarElement : IVisitable<CarElement> { }

    public class Wheel : CarElement
    {
        public string Name { get; }

        public Wheel(string name)
        {
            this.Name = name;
        }
    }

    public class Engine : CarElement { }
    public class Body : CarElement { }

    public class Car : CarElement
    {
        public IEnumerable<CarElement> Elements { get; }

        public Car()
        {
            this.Elements = new CarElement[]
            {
                new Wheel("front left"),
                new Wheel("front right"),
                new Wheel("back left"),
                new Wheel("back right"),
                new Body(),
                new Engine()
            };
        }

        public void Accept(IVisitor<CarElement> visitor)
        {
            foreach (var element in this.Elements)
            {
                element.Accept(visitor);
            }

            visitor.Visit(this);
        }
    }

    public interface IVisitable<TElement> { }

    public static class VisitableMixin
    {
        public static void Accept<TVisitor, TElement>(this IVisitable<TElement> self, TVisitor visitor)
            where TVisitor : IVisitor<TElement>
            where TElement : class
        {
            visitor.Visit(self as TElement);
        }
    }

    public interface IVisitor<TElement>
        where TElement : class
    {
        void Visit(TElement element);
    }

    public class CarElementPrintVisitor : IVisitor<CarElement>
    {
        public void Visit(CarElement element)
        {
            Console.WriteLine(element.GetType().Name);
        }
    }

    public class CarElementDoVisitor : IVisitor<CarElement>
    {
        public void Visit(CarElement element)
        {
            Console.WriteLine($"Do some other visitation: {element.GetType().Name}");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var c = new Car();
            c.Accept(new CarElementPrintVisitor());
            c.Accept(new CarElementDoVisitor());

            Console.ReadKey();
        }
    }
}