Why calling some functions of the Object class, on a primitive type instance, need boxing?

Question

I have discovered that if i run following lines of code.

int i = 7;
i.GetHashCode(); //where GetHashCode() is the derived
                 //function from System.Object

No boxing is done, but if i call i.GetType() (another derived function from System.Object ) in place of GetHashCode() , a boxing will be required to call GetType() , Why its not possible to call GetType() on primitive type instance directly, without boxing, while its possible to call GetHashCode() without boxing ?

Answer 1

The key here is that GetType() is not virtual and cannot be overridden. Since a struct is effectively sealed , methods cannot be overridden any more than the struct, so the runtime and compiler can treat struct methods that have been overridden as static calls.

If you write a struct (rare) you should override all the methods like ToString() , Equals() , GetHashCode() for exactly this reason. If you don't it must box. However, GetType() cannot be overridden, thus needs boxing.

This actually leads to some odd edge-cases with Nullable<T> and boxing, since an empty Nullable<T> boxes to null , so:

int i = obj.GetHashCode(); // fine
Type t = obj.GetType(); // boom

Answer 2

I think the reason is that GetHashCode is implemented on System.Int32 directly, you call System.Int32::GetHashCode(). No need to box if you call a known member function on a value type.

Answer 3

Seems very close to How is ValueType.GetType() able to determine the type of the struct ?

Also related is GetType and TypeOf confusion