Boxing and Unboxing (C# Programming Guide)
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.
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
Performance
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.
Related Sections
For more information:
C# Language Specification
For more information, see the following section in the C# Language Specification:
- 4.3 Boxing and Unboxing