Boxing x Unboxing

Boxing and unboxing is not to be confused with downcast / upcast.

  • Boxing is the process of converting a value type to the type object or to any interface type implemented by this value type.
  • When the CLR boxes a value type, it wraps the value inside a System.Object and stores it on the managed heap.
  • Unboxing extracts the value type from the object.
  • Boxing is implicit
  • Unboxing is explicit.
  • The concept of boxing and unboxing underlies the C# view that a value of any type can be treated as an object.



int i = 123;
// The following line boxes i. 
object o = i;


o = 123;
i = (int)o;  // unboxing

Reference: MSDN


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