reimplementing an interface in a derived class

Ali Çehreli acehreli at
Fri Jan 4 23:05:11 UTC 2019

On 01/04/2019 01:08 PM, Ali Çehreli wrote:

 > There is only one vtbl per class object

Correcting myself after reading Neia Neutuladh's post: I should have 
said "There is only one vtbl per class type". Every class object has a 
vtbl pointer that points at its type's vtbl.

So, it's normally two pointer hops to execute a virtual function:

1) Get the object's vtbl pointer to reach the vtbl of that type; pseudo 

   v = o.vtbl_ptr

2) Get the function pointer from a slot in that table (assuming foo() 
happens to be at index 5); pseudo code:

   f = v[5]  // This must be a generic type like void*

3) Call the function by passing arguments; pseudo code:

   alias F = TheActualTypeOfTheMemberFunction;
   (cast(F)f)(42, "hello", ...)


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