Async Function in WCF Service

Below are the classes and interface to host a service

ICalc.cs

using System;

using System.ServiceModel;

namespace ConsoleService

{

    [ServiceContract]

    interface ICalc

    {

        [OperationContract(AsyncPattern = true)]

        IAsyncResult BeginAdd(int a, int b, AsyncCallback callback, object asyncState);

        int EndAdd(IAsyncResult result);

        [OperationContract]

        int Sub(int a, int b);

    }

}

Calc.cs

using System;

namespace ConsoleService

{

    class Calc : ICalc

    {

        Func<int, int, int> add = (n1, n2) => n1 + n2;

        public IAsyncResult BeginAdd(int a, int b, AsyncCallback callback, object asyncState)

        {

            return add.BeginInvoke(a, b, callback, asyncState);

        }

        public int EndAdd(IAsyncResult result)

        {

            return add.EndInvoke(result);

        }

        public int Sub(int a, int b)

        {

            return a - b;

        }

    }

}

Service.cs

using System;

using System.ServiceModel;

using System.ServiceModel.Description;

namespace ConsoleService

{

    class Service

    {

        static void Main(string[] args)

        {

            ServiceHost host = new ServiceHost(typeof(Calc), new Uri("http://localhost:8888/async"));

            host.Description.Behaviors.Add(new ServiceMetadataBehavior() { HttpGetEnabled = true });

            host.Open();

            Console.Title = "Async Service";

            Console.ReadKey();

        }

    }

}

Below is the class which have the code to access the service

Client.cs

using System;

namespace ConsoleClient

{

    class Client

    {

        static void Main(string[] args)

        {

            ServiceAsync.CalcClient client = new ServiceAsync.CalcClient();

            Console.WriteLine(client.Add(2, 5));

            Console.ReadKey();

        }

    }

}