C# : Partial class , Indexers, Optional parameters for methods : Part 26

Partial class

• It allows us to split class into 2 or more files. All these partial classes are than combined to form single class when application is compiled.
• Spreading class over multiple files as partial class allows multiple programmers to work on it simultaneously.

Indexers

• Default index provided by .net is called indexers, It can be int or string.
• Indexers are generally used in list, arrays, dictionary's, etc.

Optional parameters for method

• Parameter arrays : Refer following e.g.

 namespace OptionalParameter  
 {  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       var MyResult = AddNumbers(new int[] { 2, 8, 9 });  
     }  
     public static int AddNumbers(params int[] Num)  
     {  
       int result = 0;  
       foreach (int item in Num)  
       {  
         result = result + item;  
       }  
       return result;  
     }  
   }  
 }  



• Method overloading : Write method with same declaration which tekes different input as parameters, refer following e.g.
• In following example you can see that there are 2 method with same name, but it has different parameter as i/p.

 namespace OptionalParameter  
 {  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       var MyResult = AddNumbers(4, 67);  
     }  
     public static int AddNumbers(int a, int b)  
     {  
       return a + b;  
     }  
     public static int AddNumbers(params int[] Num)  
     {  
       int result = 0;  
       foreach (int item in Num)  
       {  
         result = result + item;  
       }  
       return result;  
     }  
   }  
 }  



• Specifying parameters default : if i/p parameter is made null in parentheses itself, than that parameter becomes as optional.
• Consider following e.g.

 namespace OptionalParameter  
 {  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       var MyResult = AddNumbers(4, 67);  
     }  
     public static int AddNumbers(int a, int b, int[] Num = null)  
     {  
       int result = 0;  
       result = a + b;  
       if (Num != null)  
       {  
         foreach (int item in Num)  
         {  
           result = result + item;  
         }  
       }  
       return result;  
     }  
   }  
 }  

• In example below b and c are given by default, so if we pass only one parameter i.e. "a", but we will be getting addition result of all three a+b+c
• If we want to pass a new value to a default value than see example below

 namespace OptionalParameter  
 {  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       var MyResult = AddNumbers(2);  
     }  
     public static int AddNumbers(int a, int b = 6, int c = 30)  
     {  
       return a + b + c;  
     }  
   }  
 }  



• Using [Optional] attribute provided by interop services : Refer e.g. below
• Available in library : using System.Runtime.InteropServices;

 namespace OptionalParameter  
 {  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       var MyResult = AddNumbers(4, 67);  
     }  
     public static int AddNumbers(int a, int b, [Optional]int[] Num)  
     {  
       int result = 0;  
       result = a + b;  
       if (Num != null)  
       {  
         foreach (int item in Num)  
         {  
           result = result + item;  
         }  
       }  
       return result;  
     }   
   }  
 }