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New feature in .NET 4.0 : Optional parameters -- Step by Step to Advanced -- Part 1

Optional Parameters:

.NET introduced a new feature called Optional parameters in the version 4.0, where you can leave a particular parameter in the calling method and CLR will automatically assign the default value (That you need to provide prior)


Example:

Let's have a Console Application to discuss this,


    class Program
    {
        static void Main(string[] args)
        {
            MyClass myclass = new MyClass();
            myclass.MyMethod();

            Console.ReadLine();
        }
    }


    class MyClass
    {
        public void MyMethod()
        {
            Console.WriteLine("In MyMethod - No Parameters");
        }

    }



Output:

In MyMethod - No Parameters
Adding one more MyMethod with a single int parameter
        public void MyMethod(int a = 10)
        {
            Console.WriteLine("In MyMethod - Single Parameters");

        }

 Then calling

            myclass.MyMethod();

What will be the output?

Obviously

 In MyMethod - No Parameters


To Expand further


        static void Main(string[] args)
        {
            MyClass myclass = new MyClass();
            //myclass.MyMethod();


            myclass.MyMethod(1, 5);
            Console.ReadLine();
        }

// Adding a Overload Method


    class MyClass
    {
        public void MyMethod()
        {
            Console.WriteLine("In MyMethod - No Parameters");
        }

        public void MyMethod(int a, int b)
        {
            Console.WriteLine("a is :{0} ", a);
            Console.WriteLine("b is :{0} ", b);

            Console.WriteLine("In MyMethod - With Parameters int a, int b");
        }
    }


Output

a is :1
b is :5
In MyMethod - With Parameters int a, int b


And here comes the optional parameter:


        public void MyMethod(int a, int b = 8)
        {
            Console.WriteLine("a is :{0} ", a);
            Console.WriteLine("b is :{0} ", b);

            Console.WriteLine("In MyMethod - With Parameters int a, int b");
        }

Assigning the value in the called method will do the magic, but we still need to go further,


            MyClass myclass = new MyClass();
         
            myclass.MyMethod(1, 5);


This will not invoke the optional parameters to work, because we're passing the value in the calling method

so obviously the output will be

a is :1
b is :5
In MyMethod - With Parameters int a, int b

Ok then how to test the Optional Parameters? 

Here is the answer


            MyClass myclass = new MyClass();

            myclass.MyMethod(1);

Note that we're intentionally left the parameters for b

Then the output will be


a is :1

b is :8
In MyMethod - With Parameters int a, int b

Lets dig more into this by adding more methods


        // Adding another overload method with double parameter

        public void MyMethod(double db)
        {
            Console.WriteLine("In MyMethod (One Double input)- With Parameters Double ab);
        }


Lets call Again the same method,

            myclass.MyMethod(1);

and the output will be (Same)

a is :1
b is :8
In MyMethod - With Parameters int a, int b

Because the CLR is looking for the exact match of the signature (here the input is of type int) so it hits the early method (with a two input as parameters)

  public void MyMethod(int a, int b)


Ok, then now, adding one more caller, 

            myclass.MyMethod(1.0);

Note that we're passing the exact signature type of Double,

Then the output will be

In MyMethod (One Double input)- With Parameter Double ab


So what's the catch, we can look that in the next part,


Meantime the full program for this module is



namespace OptionalParameters
{
    class Program
    {
        static void Main(string[] args)
        {
            MyClass myclass = new MyClass();

             //myclass.MyMethod();

             /*             
              myclass.MyMethod();            
              myclass.MyMethod(1, 5);           
              myclass.MyMethod(1);          
              */
            myclass.MyMethod(1.0); 
            Console.ReadLine();
        }
    }
    class MyClass
    {
        public void MyMethod()
        {
            Console.WriteLine("In MyMethod - No Parameters");
        }
        public void MyMethod(int a = 10)
        {
            Console.WriteLine("In MyMethod - Single Parameters");
        }
        public void MyMethod(int a, int b = 8)
        {
            Console.WriteLine("a is :{0} ", a); Console.WriteLine("b is :{0} ", b);
            Console.WriteLine("In MyMethod - With Parameters int a, int b");
        }
        
        // Adding another overload method with double parameter 
        public void MyMethod(double db)
        {
            Console.WriteLine("In MyMethod (One Double input)- With Parameters int a, int b");
        }
    }

}







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