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C# 4.0 Features

, 6 May 2009 CPOL
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This article demostrates some of the exciting features in the upcoming C# 4.0.


After watching Anders Hejlsberg’s session, The Future of C# on Channel 9, I was excited to get my hands on the upcoming features of C#. Since the inception of C#, each version bought some major changes and amendments in the language. For example, in C# 1.0, the major theme was Managed Code. Then in C# 2.0, Generics were introduced and lastly in C# 3.0 LINQ was introduced. C# 4.0 introduced the concept of Dynamic Programming in C#. Overall there are four main features that are introduced in the upcoming C# 4.0:

  1. Dynamic Typed Objects
  2. Optional and Named Parameters
  3. Improved COM Interoperability
  4. Co- and Contra-Variance

Today, we will see the first two features, i.e. Dynamic Typed Object, Optional Parameters and Named Argument. A document related to New Features in C# is available at MSDN that explains all of the above features in a little detail. Plus if you are interested in getting an early look at Visual Studio 2010 CTP, you can follow my post on Visual Studio 2010 CTP. Please note that this article is written using CTP version. The final product and its features may change upon final release.

Dynamic Programming

C# 4.0 supports Dynamic Programming by introducing new Dynamic Typed Objects. The type of these objects is resolved at run-time instead of at compile-time. A new keyword dynamic is introduced to declare dynamic typed object. The keyword tells the compiler that everything to do with the object, declared as dynamic, should be done dynamically at the run-time using Dynamic Language Runtime(DLR). Remember dynamic keyword is different from var keyword. When we declare an object as var, it is resolved at compile-time whereas in case of dynamic, the object type is dynamic and it's resolved at run-time. Let’s do some coding to see the advantage of Dynamic Typed Objects. Smile | :)

A year ago, I wrote a code of setting the property of an object using Reflection:

   1:  Assembly asmLib= Assembly.LoadFile(@"C:\temp\DemoClass\bin\Debug\DemoClass.dll");
   2:  Type demoClassType = asmLib.GetType("DemoClass.DemoClassLib");
   3:  object demoClassobj= Activator.CreateInstance(demoClassType);
   4:  PropertyInfo pInfo= demoClassType.GetProperty("Name");
   5:  pInfo.SetValue(demoClassobj, "Adil", null);

Notice lines 3-5 create instance of ‘demoClassType’ and set property ‘Name’ to ‘Adil’. Now with C# 4.0, line # 3-5 can be written as simple as:

dynamic dynamicDemoClassObj = Activator.CreateInstance(demoClassType);
dynamicDemoClassObj.Name = "Adil";

Simple, isn't it? Let’s see a slide from Anders Hejlsberg’s session at PDC 2008:


From the above slide, you can call method(s) such as x.ToString(), y.ToLower(), z.Add(1), etc. and it will work smoothly. Smile | :)
This feature is great and provides much flexibility for developers. Of course there are pros and cons of dynamic programming as well but where C# is going is something like having features of both static languages and dynamic languages.

Optional Parameters

The second feature is Optional Parameters. Let’s say I have a class Employee and I provide few overloads of the constructor to enable making certain parameters as optional as follows:

 public class Employee
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Qualification { get; set; }
        public string MiddleName { get; set; }

        public Employee(string firstName, string lastName)
            FirstName= firstName;
            LastName= lastName;
            Qualification= "N/A";
            MiddleName= string.Empty;
        public Employee(string firstName, string lastName, string qualification)
            FirstName= firstName;
            LastName= lastName;
            Qualification= qualification;
            MiddleName= string.Empty;

        public Employee(string firstName, string lastName, string qualification,
            string middleName)
            FirstName= firstName;
            LastName= lastName;
            Qualification= qualification;
            MiddleName= middleName

With C# 4.0, you need to create just one constructor for that as follows:

public Employee(string firstName, string lastName,
            string qualification = "N/A", string middleName = "")
    FirstName= firstName;
    LastName= lastName;
    Qualification= qualification;
    MiddleName = middleName;

As simple as that Smile | :) and you can easily call that as follows:


This feature was available in some other languages but was for some reason not provided in C# yet, but now it’s available. This feature has a good impact in COM interop which allows developers to skip missing parameters which we will hopefully see in later post(s). Finally, the compiler will always fill the optional parameters by their default given values, if you do not provide them. For instance, in our current case, it will be:

Employee emp= newoyee("Adil", "Mughal");

Simple but useful feature!

Named Argument

So, we discussed an example of Employee class in which we passed some optional parameters in the constructor:

public Employee(string firstName, string lastName, 
	string qualification = "N/A", string middleName = "")

And I can simply call that as shown below:

Employee emp= new Employee("Adil", "Mughal");

A question can be raised "Is there any way that we can skip qualification, i.e. third parameter and give the last parameter of middleName?"

The answer of this question is "Yes absolutely, we can and that feature is called Named Argument in C# 4.0." We can simply do this like:

Employee emp = new Employee("Adil", "Mughal", middleName: "Ahmed");

Good enough to answer the query. Smile | :) . Now let’s make some changes with the Employee constructor and make lastName optional as well:

public Employee(string firstName, string lastName = "", 
		string qualification = "N/A", string middleName = "")

Now I can instantiate object of Employee in quite simple and flexible ways:

Employee("Adil", qualification:"BS");
Employee("ABC", lastName: "EFG", qualification: "BS");
Employee("XYZ", middleName: "MNO");


These upcoming features are really cool as they will enable C# developers to be more productive with the help of dynamic programming and optional parameters though some of the features are not new in the programming languages’ world.


  • 5th May, 2009: Initial version


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Adil Mughal
Technical Lead
Pakistan Pakistan
Adil is Software Engineer by profession and passion. He has extensive experience on Microsoft Development Platform and is also Microsoft Certified Professional Developer (MCPD) for Web. He has been thrice awarded as Microsoft Most Valuable Professional (MVP) due to his technical leadership in community and sharing of knowledge voluntarily.
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Comments and Discussions

GeneralMy vote of 5 Pinmemberrama charan12-Jul-12 20:25 
GeneralMy vote of 5 Pinmemberqadirv28-Jan-12 5:26 
QuestionLINQ Result as DYNAMIC Pinmembersudheer muhammed19-Apr-11 21:01 
GeneralNice Article Pinmemberarpitgold2-Apr-11 4:21 
GeneralNice and easy to understand... PinmemberSkGyan13-May-09 20:13 
GeneralVisual basic no thanks PinmemberStanley Gillmer12-May-09 4:22 
GeneralPurpose of named arguments PinmemberBoudino11-May-09 22:41 
AnswerRe: Purpose of named arguments Pinmembertomi_212-May-09 0:03 
GeneralRe: Purpose of named arguments PinmemberBoudino12-May-09 1:02 
GeneralRe: Purpose of named arguments Pinmembertomi_212-May-09 2:07 
GeneralRe: Purpose of named arguments Pinmemberronaldhobbs12-May-09 4:14 
GeneralRe: Purpose of named arguments Pinmemberssrdjan12-May-09 4:28 
GeneralRe: Purpose of named arguments [modified] Pinmemberhoria6712-May-09 6:04 
GeneralNice and Easy to Understand PinmemberMember 29924898-May-09 22:01 
GeneralRe: Nice and Easy to Understand PinmemberAdil Mughal8-May-09 22:21 
GeneralI very liked the "Optional and Named Parameters" feauture PinmemberReuven2228-May-09 3:40 
GeneralGood one.. PinmemberAbhishek Sur7-May-09 1:41 
GeneralRe: Good one.. PinmemberAdil Mughal7-May-09 2:30 
Generalgood one! PinmemberJason Law6-May-09 23:39 
GeneralRe: good one! PinmemberAdil Mughal7-May-09 2:28 
GeneralPowered by PHP Pingroupadatapost6-May-09 16:47 
GeneralRepeat PinmemberPIEBALDconsult6-May-09 15:43 
GeneralRe: Repeat [modified] PinmemberAdil Mughal6-May-09 16:54 
Thanks for mentioning that link Smile | :) I just wrote and submitted it Smile | :)
btw I think sometimes its good to have information from different sources in order to have better understanding...
Adil Mughal - MCP
modified on Wednesday, May 6, 2009 11:46 PM

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