Re: How does inheritance and vtables work wrt. C++ and interop with D? Fns w/ Multiple-inheritance args impossible to bind to?

[Gavin Ray via Digitalmars-d-learn]

On Tuesday, 25 May 2021 at 06:02:55 UTC, evilrat wrote:
Anyway all this stuff requires thorough research & testing as 
such ABI tinkering is very easy to mess up and very hard to 
debug, for example if you mess up the order(functions layout) 
it can land on another final method call that seemingly work 
but in debugger you'll see that you can't hit breakpoint in 
that method.
Happy debugging time!

Ahh, that works!

It also works without the `cast(BaseType)` if you use `alias` in 
the class:
```d
import core.stdc.stdio : printf;
extern (C++)
{
  void takesADerived(Derived derived);
  Derived createTestDerivedCPP();

  extern interface Base1
  {
    void overrideMe1();

    pragma(mangle, "?getSomething@Base1@@QEAA?BHXZ")
    final int getSomething();

    pragma(mangle, "?inheritedFunctionWithArgs@Base1@@QEAAHHH@Z")
    final int inheritedFunctionWithArgs(int x, int y);
  }

  extern interface Base2
  {
    void overrideMe2();

    pragma(mangle "?getOtherThing@Base2@@QEAA?BHXZ")
    final int getOtherThing();
  }

  extern class Derived : Base1, Base2
  {
    int someInt;

    alias getSomething = Base1.getSomething;
    alias inheritedFunctionWithArgs = 
Base1.inheritedFunctionWithArgs;

    this(int someIntVal) { this.someInt = someIntVal; }

    void overrideMe1() { printf("[D] Dlang Derived overrideMe1 
called \n"); }
    void overrideMe2() { printf("[D] Dlang Derived overrideMe1 
called \n"); }
  }
}

void main()
{
  Derived dlangDerived = new Derived(123);
  printf("[D] Derived.Base1::getSomething() = %d \n", 
dlangDerived.getSomething());
  printf("[D] Derived.Base2::getOtherThing() = %d \n", 
dlangDerived.getOtherThing());
  printf("[D] Derived.Base1::inheritedFunctionWithArgs(5, 10) = 
%d \n",
      dlangDerived.inheritedFunctionWithArgs(5, 10));
  printf("[D] Calling C++ takesADerived() with D Derived* \n");
  takesADerived(dlangDerived);
}
```

![output](https://i.imgur.com/Plbtlow.png)

Just you wait, I'll learn enough to be of any use contributing to 
OMG yet! haha