Optional Parameters in C# 4.0

Adil Mughal · April 18, 2009 at 3:20 pm

Thanks Tooba!

Bobby Cannon · July 21, 2009 at 12:21 pm

Wouldn’t the orginal code look more like this?

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)
: this(firstName, lastName, “N/A”, string.Empty)
{
}

public Employee(string firstName, string lastName, string qualification)
: this(firstName, lastName, qualification, string.Empty)
{
}

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

Jon and Judy Glick · July 21, 2009 at 2:06 pm

This is fabulous! Overloaded methods are ok, but I get tired of making sure I’ve covered all the variations I need. Looking forward to optional parameters!

Anonymous · July 21, 2009 at 5:48 pm

Yay! Another great, ages-olde VB standard Productivity Feature finds its way to the upstart 🙂

Keep them coming… eventually we’ll have all of what made Visual Basic the (still) most used programing tool in the world.

btw: I’m a C# person now… but I will always respect VB.

Anonymous · July 21, 2009 at 6:38 pm

The parameters can also be passed out of method’s signature order. Eg:

Employee e = new Employee(lastName: “Name”, firstName: “My”, middleName: “Middle”)

Anonymous · July 22, 2009 at 6:40 am

For the ridiculous lists of optional parameters in Office Automation COM interop, a solution has been available since .NET 1.0 – merely generate your own assembly and change the declaration to parameter object[] p

Optional parameters are a mild convenience at best, and a mild hazard (they afford yet another opportunity for implicit behavioural dependencies likely to cause breaking changes across versions)

Anonymous · July 22, 2009 at 5:47 pm

Not sure how I feel about these fundamental changes to the language. In fact, I’m pretty sure I won’t be using any of them unless the _need_ arises; I’ll stick with C# 2.0 language specifications, maybe with some LINQ thrown in if I’m in a good mood.

VB was a powerful language and had its own quirks. I hate to see the only difference between C# and VB become curly braces and semicolons.

Anonymous · July 23, 2009 at 7:43 am

Finally… This was the one thing that stopped most of my C# migration projects before they even started…
THANKS to Microsoft for at last listening.

denism · July 23, 2009 at 12:21 pm

@Dragan

You will call it new Employee(firstName: “Adil”, lastName: “Mughal”, middleName: “A.”).

@All
Yes, this is a great feature. However, I’m a bit disappointed that the default parameters are available for value types only. Having ability to pass “null” as a default for reference types would be great.

Anonymous · July 24, 2009 at 6:06 pm

I quickly got over the omission of optional params with the following notation:

Employee newEmp = new Employee()
{
FirstName = firstName,
LastName = lastName,
Qualification = qualification,
MiddleName = middleName
}

of course this throws integrity out the window and requires the consumers of the code to know what they’re doing, but when I’m the only one involved, that doesn’t bother me too much, as the bases are covered. 😀

Chris · July 28, 2009 at 6:25 pm

Who said anything about only passing value types? A string is an object, you should be able to pass null as a default value… for example:

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

which would pass

Employee(“Adil”, “Mughal”, null, null);

Anonymous · July 29, 2009 at 2:52 pm

For the two optional parameters, first is “N/A” and the other is just “”. Does it makes any difference? Can I give reverse such that “” and “N/A” or all the parameters “N/A” or just “”?

RaimondB · July 30, 2009 at 9:31 am

I like the idea of optional parameters, but C#3.0 intializers solve this problem also for the most some part. You could opt to only provide mandatory arguments as a constructor. And set the rest using properties when needed.

Eg.

public Employee(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
Qualification = “N/A”;
MiddleName = string.Empty;
}

And use it like this:

new Employee(“myFirstName”, “myLastName”){Qualification = “My Qual”};

Anonymous · July 31, 2009 at 2:44 pm

I think this is at last a step gone forward, for those programmers thinking this is a bad idea, wait until you create a class or function with 5 to 10 overloads.. yes it doesn’t happen every day and only in very extreme cases, but managing one constructor with a few optional values is way easier than trying to manage 5 or more…. same goes for functions, if you think that there is something wrong with writing 10 overloads, just look at Convert.ToString(“36”); 36 overloads..
it happens..

Gode · August 2, 2009 at 9:09 am

At last you have included this feature. I was wondering why it was not included in older versions of .NET but now we have it. Thank You!

Adil Mughal · August 4, 2009 at 4:23 am

@Jason: Yes you are right. The concept of named argument is mentioned in another post 🙂

Plese visit : http://adilamughal.blogspot.com/2009/04/c-40-named-argument.html

Anonymous · August 6, 2009 at 6:43 pm

Why can’t C# have true optional parameters like C++ does.

public void FunctionName(int item, int item2, int item3=0, String name=String.Empty)
{
// do stuff
}

?????

GregW · August 12, 2009 at 3:07 pm

Paul commented:

‘Tell me, how do I know if “N/A” was set by the user or if it is the default from the optional?? Answer: You don’t and that is BAD!!’

The correct answer is that if you care about whether you got the N/A as a result of an explicit vs default argument, you’re doing something wrong.

Rajkumar · August 25, 2009 at 10:04 am

Correct me if i’m wrong the above functionality can be done
if the functionality of all overloaded functions is almost same else if the functionality it self is different according to method signature then i hope it shud b inscribed in a if else loop which is again looks like a performance head.

I have understood the syntax of it but can u xplain me how it will impove performance by any case…

Himanshu Saxena · January 4, 2010 at 8:59 am

This feature has been there in c++ since ages