[Issue 18966] New: extern(C++) constructor should match C++ semantics assigning vtable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18966

          Issue ID: 18966
           Summary: extern(C++) constructor should match C++ semantics
                    assigning vtable
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: critical
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: turkeyman at gmail.com

test.cpp
------------------------------------------------
class Base
{
public:
        Base() { x = 10; }
        virtual ~Base() {}
        virtual void vf()
        {
                x = 100;
        }
        int x;
};
Base base;
------------------------------------------------

test.d
------------------------------------------------
extern(C++):
class Base
{
        this();
        ~this();
        void vf();
        int x;
}
class Derived : Base
{
        this()
        {
                super();
        }
        override void vf()
        {
                x = 200;
        }
}
void test()
{
        Derived d = new Derived;
        d.vf();
        assert(d.x == 200);
}
------------------------------------------------

When deriving a D class from a C++ class, the vtable assignment semantics are
incompatible.

D assigns the vtable once prior to construction.
C++ assigns the vtable at the start of the ctor, immediately following the call
to super.ctor().

extern(C++) class will need to loosely follow the C++ semantic, that is:
Inside any extern(C++) constructor, any call to a super constructor must
immediately be followed by assignment of the classes vtable.

--