boxing and unboxing

In C#, boxing and unboxing are concepts related to converting value types (such as int, char, etc.) to reference types (such as object). Let’s explore both concepts with examples:

1. Boxing:

   • Boxing is the process of converting a value type to the type object or any interface type implemented by that value type.
   • When the Common Language Runtime (CLR) boxes a value type, it wraps the value inside an object instance and stores it on the managed heap.
   • Here’s an example of boxing:

     int i = 123; // The following line boxes 'i'.
     object o = i;
     

   • In this example, the integer variable i is boxed and assigned to the object variable o.

2. Unboxing:

   • Unboxing is the process of extracting the value type from an object.
   • It converts the object back to its original value type.
   • Example of unboxing:

     o = 123; // Unboxing: extract the value from 'o' and assign it to 'i'.
     int unboxedValue = (int)o;
     

3. Practical Example:

   • Let’s create a heterogeneous collection using an ArrayList (a dynamically sized array of objects):

     ArrayList mixedList = new ArrayList();
     mixedList.Add("First Group:"); // Add a string element
     for (int j = 1; j < 5; j++)
     {
         mixedList.Add(j); // Add integers (boxing occurs)
     }
     mixedList.Add("Second Group:");
     for (int j = 5; j < 10; j++)
     {
         mixedList.Add(j);
     }
     
     // Display the elements in the list
     foreach (var item in mixedList)
     {
         Console.WriteLine(item);
     }
     
     // Calculate the sum of squares of the first group of integers
     var sum = 0;
     for (var j = 1; j < 5; j++)
     {
         sum += (int)mixedList[j] * (int)mixedList[j]; // Unboxing
     }
     Console.WriteLine($"Sum: {sum}"); // Output: Sum: 30
     

   • In this example, we box integers when adding them to the ArrayList and unbox them during the sum calculation.

Remember that boxing and unboxing have performance implications, so use them judiciously.