Visual Basic 2008 Core Elements - Boxing

Normally, when a conversion (implicit or explicit) occurs, the original value is read from its current memory location, and then the new value is assigned. For example, to convert a Short to a Long, the system reads the two bytes of Short data and writes them to the appropriate bytes for the Long variable. However, under Visual Basic, if a value type needs to be managed as an object, then the system performs an intermediate step. This intermediate step involves taking the value on the stack and copying it to the heap, a process referred to as boxing. As noted earlier, the Object class is implemented as a reference type, so the system needs to convert value types into reference types for them to be objects. This doesn’t cause any problems or require any special programming, because boxing isn’t something you declare or directly control, but it does affect performance.