Assign void function in D for callbacks

See more:

C

Hi all,

I need to wrap functions from a C API into D. As I have read in the DLang forums and the tutorial it should be sufficient to declare the C functions as extern (C). For the most part this works well as I am able to call the functions, which are imported as a lib.

Now I have one remaining problem. In the C API there are callbacks that I cannot connect to in D. The D wiki says that in the C code there should be a function called getCallback() which returns the void typedef of the callback. However, I only have the typedef declaration in C and no function that delivers the callback. When I try to assign the callback function in D I get compilation errors because I (obviously) cannot assign a function with no return value to a variable.

In Code it looks like this, where Events is a struct that has members like OnData declared as Callbacks:
C:

typedef void (*Callback)(void*);
void MyDtaCB(void* pVoid); // has no prototype in the API

Events.OnData = MyDtaCB;

D:

extern (C) alias HmsCEventCallback_t = int function(int, int);
extern (C) HmsCEventCallback_t MyDtaCB(void*);

// compilation error: should be called with (), but that does not work either since it returns void
Events.OnData = MyDtaCB; 

The callback alias declaration is straight from the D wiki. Still, in their example they have a function in C called getCallback() which is not available in my lib. It should look like this:

extern "C" Callback getCallback(void)
{
    return MyDtaCB;
}

I have now tried many ways to get this working. I think that the assignment of the callback in D would be as simple as in C but, as mentioned above, I get the compilation error.

So how can I get this done without having to modify the C API?

Any suggestions would be appreciated.