Boxing
- 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 reference type variable and must be assigned a reference to an object in the heap.
- Variable i, however, is a value type and doesn’t have a reference to an object in the heap.
- 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
The system therefore box the value of i by doing the following:
Memory is allocated on the heap that will contain the value type’s data and the other overhead necessary to make the object look like
every other instance of a managed object of reference type .
The value of the value type is copied from its current storage location into the newly allocated location on the heap.
The result of the conversion is a reference to the new storage location on the heap.
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int i; object oi; i = 42; // Boxing oi = i; |
Unboxing
What is UnBoxing Conversion?
Unboxing is the process of converting a boxed object back to its value type.Unboxing is an explicit conversion.
The system performs the following steps when unboxing a value to ValueTypeT:
It checks that the object being unboxed is actually a boxed value of type ValueTypeT.
It copies the value of the object to the variable.