Proxy Design Pattern

This code demonstrates the Remote Proxy pattern which provides a representative object (i.e., a stand-in object) that controls access to another object in a different AppDomain.

using System;
using System.Runtime.Remoting;

namespace Patterns
{
    
    class MainApp
    {
         
        static void Main()
        {
             // Create math proxy
            MathProxy proxy = new MathProxy();

             // Do the math
           Console.WriteLine("4 + 2 = " + proxy.Add(4, 2));
           Console.WriteLine("4 - 2 = " + proxy.Sub(4, 2));
           Console.WriteLine("4 * 2 = " + proxy.Mul(4, 2));
           Console.WriteLine("4 / 2 = " + proxy.Div(4, 2));

             // Wait for user
           Console.ReadKey();
        }
     }

    /// <summary>
    /// The 'Subject' interface
    /// </summary>
    public interface IMath
    {
         double Add(double x, double y);
        double Sub(double x, double y);
        double Mul(double x, double y);
        double Div(double x, double y);
    }

    /// <summary>
    /// The 'RealSubject' class
    /// </summary>
    class Math : MarshalByRefObject, IMath
    {
         public double Add(double x, double y) { return x + y; }
        public double Sub(double x, double y) { return x - y; }
        public double Mul(double x, double y) { return x * y; }
        public double Div(double x, double y) { return x / y; }
    }

    /// <summary>
    /// The remote 'Proxy Object' class
    /// </summary>
    class MathProxy : IMath
    {
         private Math _math;

        // Constructor
        public MathProxy()
        {
             // Create Math instance in a different AppDomain
           AppDomain ad =
               AppDomain.CreateDomain("MathDomain", null, null);

           ObjectHandle o = ad.CreateInstance(
                 "DoFactory.GangOfFour.Proxy.NETOptimized",
                 "DoFactory.GangOfFour.Proxy.NETOptimized.Math");
            _math = (Math)o.Unwrap();
        }

         public double Add(double x, double y)
        {
             return _math.Add(x, y);
        }

         public double Sub(double x, double y)
        {
             return _math.Sub(x, y);
        }

        public double Mul(double x, double y)
        {
             return _math.Mul(x, y);
        }

        public double Div(double x, double y)
        {
             return _math.Div(x, y);
        }
    }
}