Optional parameters (Use and Limitation)

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.