What's New in C# 4.0

1) Optional Parameters

public class Order
{
//Old way
   public int Purchase(Product product, Customer customer, bool isResale, string     discountCode)
   {
       
   }
// New way
   public int Purchase(Product product, Customer customer, bool isResale = false, string discountCode = string.Empty)
   {
   }
}
public class Program
{
 static void Main(string[] args)
 {
    Order newOrder = new Order();
    Product item = new Product { ItemCode = "A8901", Price = 50, Qty = 5};
    Customer customer = new Customer();
    customer.UserName = "R887663";
    customer.PreferredCustomer = true;
    newOrder.Purchase(item, customer);
 }
}

2. Named Parameters

public class Program
{
 static void Main(string[] args)
 {
    Order newOrder = new Order();
    Product item = new Product { ItemCode = "A8901", Price = 50, Qty = 5};
    Customer customer = new Customer();
    customer.UserName = "R887663";
    customer.PreferredCustomer = true;
    newOrder.Purchase(item, customer, discountCode: 76883987);
 }
}

3. Use of dynamic keyword

static class DynamicDemo    
{
        public static void Execute()
        {
            var person = new Person { Name = "Alex" };
            var company = new Company { Name = "Microsoft" };

            DoSomething(person);
            DoSomething(company);
        }

        static void DoSomething(dynamic item)
        {
          Console.WriteLine(item.Name);
        }
    }

    class Person
    {
        public string Name { get; set; }
    }

    class Company
    {
        public string Name { get; set; }
    }

4. Use of DynamicObject

class DynamicObjectSimpleDemo : DynamicObject
    {
        private Dictionary members = new Dictionary();

        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            return this.members.TryGetValue(binder.Name, out result);
        }

        public override bool TrySetMember(SetMemberBinder binder, object value)
        {
            this.members[binder.Name] = value;
            return true;
        }
    }

public class DynamicObjectXDemo : DynamicObject
{
       private XElement element;

        public DynamicObjectXDemo (XElement element)
        {
            this.element = element;
        }

        public override bool TryGetMember(GetMemberBinder binder, out object result)
        {
            result = this.element.Attribute(binder.Name).Value;
            return true;
        }

        public override bool TrySetMember(SetMemberBinder binder, object value)
        {
            this.element.SetAttributeValue(binder.Name, value);
            return true;
        }
}

class program
{
  static void main(string[] args)
  {
    dynamic sample = new DynamicObjectSimpleDemo();
    sample.Fname = "Alex";
    sample.LName = "Palle";

     var xml = XElement.Load("Clients.xml").Elements().Select(x => new DynamicObjectXDemo(x));

            foreach (dynamic item in xml)
            {
                Console.WriteLine(item.FName+ " " + item.LName);
            }
  }
}

//Clients.xml