.NET Framework 4.0 : Optional Parameters in C# 4.0 and Limitations

[Amirpooyan Raeessi]

Introduction

In this article, I will explain how to use the optional parameter in C 4.0 and what are the limitations or points we have to keep mind before use these types of parameters in coding.

What is Optional Parameter(s) ?

In C#4.0 Optional parameter allows to create method(s) with the parameters which is having default values with it.

Syntax

Accessmodifier ReturnType NameOfMethod(Type param1, Type Pram2,....,Type Param(n-1)=DefultValue,Type Param(n)=DefultValue )
{
   //code goes here

}

Example

public void MyOptParamTest(int a, int b=10)
{
   //code goes here
}

Points To Remeber

It's very easy to implement the method with the Option Parameter(s). But one should keep in mind following points when using it

• Optional parameter(s) must come after required parameters.

//valid
public void MyOptParamTest(int a, int b=10)
//not valid
public void MyOptParamTest(int b=10,int a ) 

• But Parameter array always comes last i.e after Optional parameter(s).

//valid
public void MyOptParamTest(int a, int b=10, params int[] myArray) 

• Parameter array cannot be optional parameter

//not valid
public void MyOptParamTest(int a, int b=10,
                         params int[] myArray = null)

• Optional parameter(s) cannot be specified with ref and out keywords.

//not valid
public void MyOptParamTest(int a,ref int b=10) 

• Optional parameter(s) can have any time but value of Optional parameter(s) can be constants i.e string,int etc. , null, Enum number, const member and the default(T) operator.
• Optional parameter(s) - value types, you can call the parameterless constructor.
• Optional parameter(s) - implicit conversion from the specified value to the parameter type, but this must not be a user-defined conversion.

//valid
public void MyOptParamTest(int a,decimal b=10)
//not valid -- user defined conversion

public void MyOptParamTest(int a,
                    XTypeVariable b=10)

Where to USE ?

• Use full when coding methods where default value play good role i.e By specifying null value to option parameter(s).
          Consider case where I have method to calculate age of the person

public int CalcualteAge(DateTime birthDate,DateTime? deathDate= null)
    {
       DateTime actualEndDate = deathDate ?? DateTime.Now;

       TimeSpan dateDifference = actualEndDate.Subtract(birthDate);
       int days = dateDifference.Days;
    }

So by the above way its makes code easy.

• Decrease amount of overload method(s) where it's just become overloaded by no. of passing parameter

Consider same above case where I have method to calculate age of the person

///For person who is dead
    public int CalcualteAge(DateTime birthDate,DateTime deathDate)

    {
       TimeSpan dateDifference = deathDate.Subtract(birthDate);
       int days = dateDifference.Days;
    }
 
    ///For person who is alive
    public int CalcualteAge(DateTime birthDate)
    {

       DateTime actualEndDate =  DateTime.Now;
       TimeSpan dateDifference = actualEndDate.Subtract(birthDate);
       int days = dateDifference.Days;
    } 

But if we use Optional parameter

public int CalcualteAge(DateTime birthDate,DateTime? deathDate= null)
    {
       DateTime actualEndDate = deathDate ?? DateTime.Now;
       TimeSpan dateDifference = actualEndDate.Subtract(birthDate);
       int days = dateDifference.Days;

    } 

So by the use of the optional parameter(s) we just have one method which is do the task of two method.

Summary

Optional parameter(s) makes code small,simple and easy to understand. thank you for reading.