C#4.0 Dynamic Programming &Named Argument

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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. :)

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

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   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:

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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. :)
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:

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 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:

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

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

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Employee(“Adil”,”Mughal”);

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:

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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:

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

And I can simply call that as shown below:

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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:

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

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

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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:

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

Conclusion

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.