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In this post I will talk for one of the new feature in C# 4.0 – Named and Optional Parameter. Actually these are not a single feature but two different feature. You can get more benefit if you work with them together. So, what are those? Named parameter is a way to provide an parameter to the method using the name of the corresponding parameter instead of its position in the parameter list. Whereas, optional parameter allows you to omit arguments to member invocation.

Let us discuss it in depth with a simple example. First start with the Optional Parameter. Suppose you are creating an Calculator application where you have to do some “Add” operation by passing two, three or four parameters to the method. What will you do if you are using C# 2.0 or 3.0? You will have no other choice than creating as many methods and passing the parameters in this which is known as method overloading.

public int Add(int a, int b);
public int Add(int a, int b, int c);
public int Add(int a, int b, int c, int d);

If you are using C# 4.0 just forget about method overloading by using the optional parameter. Optional parameter is a default value passes to the method signature. Let us go for modifying our previous example to use optional parameter.

public int Add(int a, int b, int c = 0, int d = 0);

Here we are passing default value to the parameter “c” and “d”. Hence you can call this method as per your requirement like this:

Add(10, 20); // 10 + 20 + 0 + 0
Add(10, 20, 30); // 10 + 20 + 30 + 0
Add(10, 20, 30, 40); // 10 + 20 + 30 + 40

In the first case it will pass ‘0’ (zero) as the optional parameter c and d, in the second case the fourth parameter will be treated as ‘0’ (zero) and in the third case all the parameters are available with proper values.

Now, let us think that we have a situation where we are creating an account of an user with the method named “CreateAccount” which has a non-optional parameter “Name” and two optional parameters “Address” & “Age”. Here in some scenario you want to pass only the “Name” and “Age”, how can you pass? Just think on it.

public void CreateAccount(string name, string address = "unknown", int age = 0);

Are you thinking of calling the method with an empty string or null value to the “Address” parameter? Oh, not really. There comes the another new feature of C# 4.0 called as “Named Parameter”. Using this you can call the method with proper name resolution or even you can change the position of the parameter while calling the method. Have a look into the following code example:

CreateAccount("Kunal", age: 28);
CreateAccount(address: "India", name: "Kunal");

First example shows calling the method without the middle parameter “Address” and the second example demonstrates calling the same method after changing the position of the parameter in the parameter list using the name of the parameter. By this way you can create a single method with Named & Optional Parameter instead of overloading it for several times and use it everywhere you need as per your requirement. This gives a more cleaner code with less efforts. Enjoy working with this. Cheers.

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