std.traits.ReturnType b0rking on function pointer.

[Daniel Keep]

Kirk McDonald wrote:
> Daniel Keep wrote:
> 
>>
>> Hey there, I'm having problems with getting the return type of a 
>> function pointer.  Basically, I want to do this:
>>
>> template SDL_SafeCall(alias tFn)
>> {
>>     ReturnType!(SDL_SetVideoMode) SDL_SafeCall(...)
>>     {
>>         ...
>>     }
>> }
>> SDL_SafeCall!(SDL_SetVideoMode)(...);
>>
>> where SDL_SetVideoMode is declared like so (yes, it's DerelictSDL):
>>
>> typedef SDL_Surface* function(int,int,int,Uint32) pfSDL_SetVideoMode;
>> pfSDL_SetVideoMode          SDL_SetVideoMode;
>>
>> When I try to compile my code, I get the following errors:
>>
>> C:\Daniel\dmd\dmd\src\phobos\std\traits.d(34): alias 
>> std.traits.ReturnType!(pfSDL_SetVideoMode).ReturnType recursive alias 
>> declaration
>> C:\Daniel\dmd\dmd\src\phobos\std\traits.d(34): template instance 
>> std.traits.ReturnType!(pfSDL_SetVideoMode) error instantiating
>>
>> I've tried writing my own version, but that didn't do any better. 
>> Anyone have any ideas?
>>
>>     -- Daniel
> 
> 
> ReturnType has two forms: One which is intended to operate on a function 
> pointer or delegate /type/, and one which is intended to operate on a 
> function alias.
> 
> SDL_SetVideoMode is a function pointer. You want to pass its /type/ to 
> ReturnType. By passing it directly, it gets sent to the alias form of 
> ReturnType, which confuses it greatly. Try this:
> 
> ReturnType!(typeof(SDL_SetVideoMode))
> 

template SDL_Refcall(alias tFn)
{ // line 57
     ReturnType!(typeof(tFn)) SDL_Refcall(tArgs...)(tArgs args)
     {
         ReturnType!(typeof(tFn)) r = tFn(args);
         if( r is null )
             throw new SDLException(tFn.nameof, 0);
         else
             return r;
     }
}

SDL_Refcall!(SDL_SetVideoMode)(...);

No good.

C:\Daniel\dmd\dmd\src\phobos\std\traits.d(34): alias 
std.traits.ReturnType!(pfSDL_SetVideoMode).ReturnType recursive alias 
declaration
C:\Daniel\dmd\dmd\src\phobos\std\traits.d(58): template instance 
std.traits.ReturnType!(pfSDL_SetVideoMode) error instantiating
src\engine\shared_sdl\shared_sdl.d(58): Error: 
ReturnType!(pfSDL_SetVideoMode) is used as a type