Want more? Here are some additional resources on this topic:
Boxing and unboxing enable value types to be treated as objects. Boxing a value type packages it inside an instance of the Object reference type. This allows the value type to be stored on the garbage collected heap. Unboxing extracts the value type from the object. In this example, the integer variable i is boxed and assigned to object o.
i
o
int i = 123; object o = (object)i; // boxing
The object o can then be unboxed and assigned to integer variable i:
o = 123; i = (int)o; // unboxing
In relation to simple assignments, boxing and unboxing are computationally expensive processes. When a value type is boxed, an entirely new object must be allocated and constructed. To a lesser degree, the cast required for unboxing is also expensive computationally. For more information, see Performance.
For more information:
Boxing Conversion
Unboxing Conversion
Reference Types
Value Types
For more information, see the following section in the C# Language Specification:
4.3 Boxing and Unboxing