New .NET Feature - Code Contracts

using System;
using System.Diagnostics.Contracts;
using System.Diagnostics; 

namespace CodeContracts
{
    class Program
    {
        static void Main()
        {
            CalculateWithDebugAssert cwda = new CalculateWithDebugAssert(4, 0);
            Console.WriteLine("Result is {0}", cwda.Divide());

            ClaculateWithContracts cc = new ClaculateWithContracts(4, 8);
            Console.WriteLine("Result is {0}", cc.Divide());
            
            Console.ReadLine(); 
        }
    }

    class CalculateWithDebugAssert
    {
        private int num1;
        private int num2;

        public CalculateWithDebugAssert(int numberone, int numbertwo)
        {
            num1 = numberone;
            num2 = numbertwo; 
        }

        public int Divide()
        {
            Debug.Assert(num2 > 0, "numbertwo should be greater than 0"); 
            if (num2 > 0)
                return num1 / num2;

            return num1;

        }
    }

    class ClaculateWithContracts
    {
        private int num1;
        private int num2;
      

        public ClaculateWithContracts(int numberone, int numbertwo)
        {
            num1 = numberone;
            num2 = numbertwo; 
        }

        [ContractInvariantMethod]
        protected void ObjectInvariant()
        {
            Contract.Invariant(this.num2>0);
        }

        public int Divide()
        {
            Contract.Ensures(Contract.Result<int>() > 0); 
            if (num2 > 0)
                return num1 / num2;

            return num1;

        }
    }
}