Information Technology Reference
In-Depth Information
Boxing Conversions
All C# types, including the value types, are derived from type
object
. Value types, however, are
efficient, lightweight types that do not, by default, include their
object
component in the heap.
When the
object
component is needed, however, you can use
boxing
, which is an implicit con-
version that takes a value type value, creates from it a full reference type object in the heap, and
returns a reference to the object.
For example, Figure 18-22 shows three lines of code.
The first two lines of code declare and initialize value type variable
i
and reference type
variable
oi
.
In the third line of code, you want to assign the value of variable
i
to
oi
. But
oi
is a refer-
ence type variable, and must be assigned a reference to an object in the heap. Variable
i
,
however, is a value type, and does not
have
a reference to an object in the heap.
The system therefore
boxes
the value of
i
by
-
Creating an object of type
int
in the heap
Copying the value of
i
to the
int
object
-
Returning the reference of the
int
object to
oi
to store as its reference
-
Figure 18-22.
Boxing creates a full reference type object from a value type
