The runtime knows the type of every object. Boxed values are no different. Let's assume you have a Ball which is value type, you put a ball in the GlassBox. Does that prevents you from knowing it is a ball inside a glass box? You can clearly see that isn't it? Just like that.. This is a slightly confusing question. Imagine you created a Foo instance reference type , and then assigned that to an object variable. Would you not also expect the same exception if you tried to cast it to a Bar instance also a reference type?
See my edit. Add a comment. Active Oldest Votes. Int32 Boxing was very common in. NET compiler auto-generates. Hans Passant Hans Passant k gold badges silver badges bronze badges. Thanks for the precise explanation. Answers from Luaan, Paval and Ritesh also explain the same thing overall in different ways but your's hit the sweet spot.
In your example you even don't need to cast it from int to long, because it's an implicit cast. Ritesh Hingorani Ritesh Hingorani 21 3 3 bronze badges. Luaan Luaan Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. When an object box is cast back to its original value type, the value is copied out of the box and into the appropriate storage location.
Boxing conversions A boxing conversion permits any value-type to be implicitly converted to the type object or to any interface-type implemented by the value-type. Boxing a value of a value-type consists of allocating an object instance and copying the value-type value into that instance. Instead, a boxed value of type G has the dynamic type G, and a dynamic type check using the is operator can simply reference type G.
A boxing conversion implies making a copy of the value being boxed. This is different from a conversion of a reference-type to type object, in which the value continues to reference the same instance and simply is regarded as the less derived type object.
Write Point box. Had Point instead been declared a class, the value 20 would be output because p and box would reference the same instance. Unboxing conversions An unboxing conversion permits an explicit conversion from type object to any value-type or from any interface-type to any value-type that implements the interface-type.
An unboxing operation consists of first checking that the object instance is a boxed value of the given value-type, and then copying the value out of the instance. The concept of boxing and unboxing underlies the C unified view of the type system in which a value of any type can be treated as an object. In the following example, the integer variable i is boxed and assigned to object o. In relation to simple assignments, boxing and unboxing are computationally expensive processes.
When a value type is boxed, a 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. Boxing is used to store value types in the garbage-collected heap. Boxing is an implicit conversion of a value type to the type object or to any interface type implemented by this value type. Boxing a value type allocates an object instance on the heap and copies the value into the new object.
The result of this statement is creating an object reference o , on the stack, that references a value of the type int , on the heap. If thisType is a value type and thisType does not implement method then ptr is dereferenced, boxed, and passed as the 'this' pointer to the callvirt method instruction.
This last case can occur only when method was defined on Object, ValueType, or Enum and not overridden by thisType. In this case, the boxing causes a copy of the original object to be made.
However, because none of the methods of Object, ValueType, and Enum modify the state of the object, this fact cannot be detected.
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