Chapter 49: Named Arguments

Section 49.1: Argument order is not necessary

You can place named arguments in any order you want.

Sample Method:

public static string Sample(string left, string right)

{

return string.Join("-",left,right);

}

Call Sample:

Console.WriteLine (Sample(left:"A",right:"B"));

Console.WriteLine (Sample(right:"A",left:"B"));

Results:

A-B

B-A

Section 49.2: Named arguments and optional parameters

You can combine named arguments with optional parameters.

Let see this method:

public sealed class SmsUtil

{

public static bool SendMessage(string from, string to, string message, int retryCount = 5, object attachment = null)

{

// Some code

}

}

When you want to call this method without set retryCount argument :

Section 49.3: Named Arguments can make your code more clear

Consider this simple class:

class SmsUtil

{

public bool SendMessage(string from, string to, string message, int retryCount, object attachment)

{

// Some code

}

}

Before C# 3.0 it was:

var result = SmsUtil.SendMessage("Mehran", "Maryam", "Hello there!", 12, null);

you can make this method call even more clear with named arguments:

var result = SmsUtil.SendMessage( from: "Mehran",

to: "Maryam",

message "Hello there!", retryCount: 12, attachment: null);

value for the optional argument, the default value of that datatype is assigned to that argument. The Optional keyword is present in “Runtime.InteropServices” namespace.

using System.Runtime.InteropServices;

private static double FindAreaWithOptional(int length, [Optional]int width)

{

try

{

return (length * width);

}

catch (Exception)

{

throw new NotImplementedException();

}

}

area = FindAreaWithOptional(120); //area=0

And when we call the function, we get 0 because the second argument is not passed and the default value of int is 0 and so the product is 0.

Section 50.2: Named Arguments

Consider following is our function call.

FindArea(120, 56);

In this our first argument is length (ie 120) and second argument is width (ie 56). And we are calculating the area by that function. And following is the function definition.

private static double FindArea(int length, int width)

{

try

{

return (length* width);

}

catch (Exception)

{

throw new NotImplementedException();

}

}

So in the first function call, we just passed the arguments by its position. Right?

double area;

Console.WriteLine("Area with positioned argument is: "); area = FindArea(120, 56);

Console.WriteLine(area); Console.Read();

If you run this, you will get an output as follows.

If you use a named argument before a fixed argument you will get a compile time error as follows.

Named argument specification must appear after all fixed arguments have been specified