Method Parameters in .NET 4.0

People with VB6.0 background always arguing with C# developers for some nice features like optional parameters which let you make a parameter as optional. Only need to write an Optional key word with parameter. In C# we normally handle these situations by creating numerous over loadings which will increase the size of the file. At last in version 4.0 C# also came with optional parameters along with named parameters. Below explaining all these with the help of a small customized class.

Optional Parameters and Default Values

I have a class like below. The method GetDetails will return the details based on id and name. At least you should pass id. But name is not mandatory. Before 4.0 release we are implementing this by define two methods using overloading like,

ArrayList GetDetails(string id) and ArrayList GetDetails(string id, string name)

If you need to pass both parameters you will call second method. Otherwise 1st once. I personally faced lot of junk overrides like this and thought about good old VB6.0 optional parameters. That's why now in 4.0 version you only need to declare one method like below.

public class MyClass

{

public ArrayList GetDetails(string id, string name = "")

{

return new ArrayList();

}

What's the new thing here? After second parameter declaration, immediately assigning it with a value, "". So if you passed only id, name will be taken automatically with a value of "". So I can this method like below

MyClass cls = new MyClass();

//Only id passing

ArrayList list = cls.GetDetails("1");

//Both id and name passing

ArrayList list = cls.GetDetails("1", "Jaish");

You can see I am calling only one method for both scenarios by utilizing latest 4.0 version optional parameter and default value features. More over you can identify that whether any of the parameters of a method is optional through VS 2010 editor. It's so smart that identifying such parameters and showing them with a square bracket like below screen shot.

Criteria for optional parameters and default values

Optional parameters should be lined up after declared all mandatory parameters. So their position is last in parameters line up.
Default value assigning should be a compile time constant i.e. you can't assign it with "string. Empty" or any string type variable. But you need to assign it with a valid value like name ="Jaish" or even name=""

Named Parameters

I am going to add one more parameter to my method and it now look like below

public class MyClass

{

string ss = string.Empty;

public ArrayList GetDetails(string id, string name = "", string age = "")

{

return new ArrayList();

}

As I explained earlier, before 4.0 release we again will get rid of one more overloading. But in 4.0 we can call it like

ArrayList list = cls.GetDetails("1", "", "37");

If you won't compromise on productivity of a developer, of course will raise a question.

I don't want to pass second parameter, name. I only need to pass last parameter, age. So skipping specific optional parameters and passing values to only needed optional parameters can be achieved through NamedParameters. As its name reveals, we will pass the parameter name too along with assigned value.

So it can be identified that which parameters need to be taken care.

ArrayList list = cls.GetDetails("1", age: "37");

Just look above line, as I used "age" as the name of the parameter and only passed id and age. Even though between id and age there's another parameter "name", it will automatically skip. Here also VS 2010 editor is smart. Look below screen shot that it's giving all details for a Named Parameter.

Summary: All features mentioned above will increase the productivity of a developer. We are reducing lot of method overrides especially when you are porting a file which is written in C++ or VB 6.0 to C#.

4 Comments

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aman gandhi14y ago
it is showing an error "Error:Default parameter specifiers are not permitted" how to resolve it.
- Jaish Mathews14y ago
  Sorry for late reply, I saw your message though. I was going through some burning points. Any way it works e.g. public string Total(string id, string name = "", int salary = 0) { return string.Empty; } I called it both way like Total("ss", "ddd"); Total("jaish", salary: 1000000);
aman gandhi14y ago
can we use optional parameter with int type variables??
Praveen Raveendran15y ago
Its very nice to have optional parameters in methods. We have the optional parameters in VB.net i guess.