On Sunday, 23 May 2021 at 20:16:17 UTC, Ola Fosheim Grostad wrote:
On Sunday, 23 May 2021 at 19:44:01 UTC, Gavin Ray wrote:
So one of the problems with generating D code for bindings to
C++ is that there's no true/direct multiple inheritance.
If anyone happens to understand well how vtables work and the
way the compiler treats these things, is there a way to
hackily make semantically-equivalent objects?
I believe Clang and MSVC are using different layouts.
If I am not wrong clang/gcc are using the Itanium ABI, but I
could be wrong.
https://itanium-cxx-abi.github.io/cxx-abi/abi.html#vtable
Maybe ask in the LDC forum as they follow Clang? In my opinion
MI ought to be supported for binding, but... not sure if anyone
has considered it.
I guess that's maybe a better way of what I'm asking -- whether
the vtable is all that matters.
Because I've seen C ABI's for C++ API's that have multiple
inheritance, and the code was like this (I'll just post a single
inheritance example but you get the point):
```cpp
class FUnknown {
tresult queryInterface(void*, const TUID, void**);
uint32* addRef(void *);
uint32* release(void *);
};
class IComponentHandler : FUnknown {
tresult beginEdit(void *, ParamID);
tresult performEdit(void *, ParamID, ParamValue);
tresult endEdit(void *, ParamID);
tresult restartComponent(void *, int32);
};
#ifdef __cplusplus
extern "C" {
#endif
typedef struct FUnknownVTable {
tresult (*queryInterface)(void *, const TUID, void **);
uint32 (*addRef)(void *);
uint32 (*release)(void *);
} FUnknownVTable;
typedef struct SFUnknown {
FUnknownVTable *vtable;
} SFUnknown;
typedef struct IComponentHandlerVTable {
FUnknownVTable FUnknown;
tresult (*beginEdit)(void *, ParamID);
tresult (*performEdit)(void *, ParamID, ParamValue);
tresult (*endEdit)(void *, ParamID);
tresult (*restartComponent)(void *, int32);
} IComponentHandlerVTable;
typedef struct SIComponentHandler {
IComponentHandlerVTable *vtable;
} SIComponentHandler;
#ifdef __cplusplus
}
#endif
```
I don't really know anything at all about compilers or low-level
code -- but is there any high-level notion of "inheritance" after
it's been compiled?
I felt like it had to turn into something like blocks of memory
that have pointers to methods and/or to other blocks of memory
with pointers to methods (vtables). But I also have no clue 🤔
