Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
Export (0) Print
Expand All
Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.

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

C# Language Specification

For more information, see the following section in the C# Language Specification:

  • 4.3 Boxing and Unboxing

See Also

Community Additions

ADD
Show:
© 2015 Microsoft