August 10, 2011
Oh, so structs themselves are only definitions and not global variables, I see. Thanks.
October 19, 2011
I'm trying to implement the function pointer system right now, and it seems to work on the C side, but not D. I assume I'm missing some kind of syntax here. I have these global variables:

        struct S_FrontendFunctions {
            void function() RedrawScreen;
            void function(const char*, int) PrecacheCard;
        }
        shared S_FrontendFunctions FrontendFunctions;

And if I try to set the pointers D style, like this:

        FrontendFunctions.RedrawScreen = function(){};
        FrontendFunctions.PrecacheCard = function(const char*, int){};

I get errors:

        Error: cannot implicitly convert expression (__funcliteral3)
of type _error_ function() to shared(void function())
        Error: cannot implicitly convert expression (__funcliteral4)
of type _error_ function(const const(char*), int) to shared(void
function(const const(char*), int))

So how do I define those functions as shared?
November 29, 2011
I seem to have another problem with the function pointer approach. I am trying to set up a function that would pass the function pointers from C to D, and DMD refuses to compile it:

If I have the function pointer struct with D calling convention pointers, like this:

    struct S_FrontendFunctions {
        void function(int) SoundPlay;
        void function() RedrawScreen;
    }
    S_FrontendFunctions FrontendFunctions;

And I try to set it in D like this:

    FrontendFunctions.SoundPlay = function(int){};
    FrontendFunctions.RedrawScreen = function(){};

And have a function for transferring the pointer from C like this:

    extern (C):
    void SetRedrawScreen(void function() RedrawScreen)
    {
        FrontendFunctions.RedrawScreen = RedrawScreen;
    }

DMD throws an error in the last function:

    Error: cannot implicitly convert expression (RedrawScreen) of type
extern (C) void function() to void function()

Now if I define the two function pointers as extern(C) like this:

    struct S_FrontendFunctions {
        extern (C) void function(int) SoundPlay;
        extern (C)  void function() RedrawScreen;
    }

DMD still complains, but this time about when I set the pointers from D directly:

    Error: cannot implicitly convert expression (__funcliteral3) of
type void function() pure nothrow @safe to extern (C) void function()

Any ideas about how to make it work from both D and C sides?
November 29, 2011
On 2011-11-29 12:53, Dainius (GreatEmerald) wrote:
> I seem to have another problem with the function pointer approach. I
> am trying to set up a function that would pass the function pointers
> from C to D, and DMD refuses to compile it:
>
> If I have the function pointer struct with D calling convention
> pointers, like this:
>
>      struct S_FrontendFunctions {
>          void function(int) SoundPlay;
>          void function() RedrawScreen;
>      }
>      S_FrontendFunctions FrontendFunctions;
>
> And I try to set it in D like this:
>
>      FrontendFunctions.SoundPlay = function(int){};
>      FrontendFunctions.RedrawScreen = function(){};
>
> And have a function for transferring the pointer from C like this:
>
>      extern (C):
>      void SetRedrawScreen(void function() RedrawScreen)
>      {
>          FrontendFunctions.RedrawScreen = RedrawScreen;
>      }
>
> DMD throws an error in the last function:
>
>      Error: cannot implicitly convert expression (RedrawScreen) of type
> extern (C) void function() to void function()
>
> Now if I define the two function pointers as extern(C) like this:
>
>      struct S_FrontendFunctions {
>          extern (C) void function(int) SoundPlay;
>          extern (C)  void function() RedrawScreen;
>      }
>
> DMD still complains, but this time about when I set the pointers from
> D directly:
>
>      Error: cannot implicitly convert expression (__funcliteral3) of
> type void function() pure nothrow @safe to extern (C) void function()
>
> Any ideas about how to make it work from both D and C sides?

In stead of doing this:

FrontendFunctions.SoundPlay = function(int){};
FrontendFunctions.RedrawScreen = function(){};

Do something like this:

extern (C)
{
    void playSound (int) {};
    void redrawScreen () {};
}

FrontendFunctions.SoundPlay = &playSound;
FrontendFunctions.RedrawScreen = &RedrawScreen;

-- 
/Jacob Carlborg
November 29, 2011
Ah, I see, that makes sense. And it now compiles correctly, thanks.
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