IupSetCallback function passing

[Rikki Cattermole]

On Wednesday, 19 March 2014 at 02:21:18 UTC, James Wirth wrote:
> When trying to associate an Icallback function to a button in 
> the IUP GUI
> API using the IupSetCallback function, the D compiler seems to 
> insist on evaluating that callback in order to pass its value 
> rather than passing the function itself.
>
> I get this dmd compiler error (the source is named hitmeiup.d) :
>
> Error: function hitmeiup.hitMeAct (Ihandle_* dmy) is not 
> callable using argument types ()
> hitmeiup.d(41): Error: expected 1 function arguments, not 0
>
> for this line calling the IupSetCallback:
>
> 	IupSetCallback(btn,"ACTION",hitMeAct);
>
> The callback function was named hitMeAct as follows:
>
> extern(C) {
> 	int hitMeAct(Ihandle *dmy) {
> 		sayHit();
> 		return 0;
> 	}
> }
>
> I have also tried it with hitMeAct being a D function instead 
> of extern(C).
>
> It is as if the	call to IupSetCallback is interpreting hitMeAct 
> to be a property function and that the call was meant to be:
>
> 	IupSetCallback(btn,"ACTION",hitMeAct());
>
> It there someway to force D to consider the hitMeAct parameter 
> to be passing a function and NOT calling it?  I tried prefixing 
> a & - no go.
>
> Would welcome any hints.
>
> Yes I have already looked at the .d files purporting to provide 
> access to IUP.
> And a more or less equivalent C program works fine.

Using & to get the function pointer is correct in this case.
You may need to do a cast for the pointer to what c expects. 
However it will work fine.
The brackets forces it to call it. Don't.