Proper C Pointer Binding

["Róbert László Páli"]

I am programming a new GUI widget library based on OpenGL for D.
For that I manually bind the used OpenGL functions to D and create
an abstraction layer to draw things, boxes, texts, shapes, etc.

http://palaes.rudanium.org/HueApp/intro.php

The thing compiles nicely with SDL, FreeType, FTGL. But
for the text drawing I use some pretty lame binding currently.
It is a fresh part of the code and want to do it properly:

C Code:

unsigned long loadFont(char * path) {
   FTGLfont * font = FTGLloadFont(path);
   return (unsigned long) font;
}

void drawText(unsigned long font, unsigned size, char * text) {
   // do the text drawing here
}

void destroyFont(unsigned long font) {
   FTGLdestroyFont((FTGLfont * ) font);
}

D Code:

extern (C) ulong loadFont(char * path);

extern (C) void destroyFont(ulong font);

void main() {

   // init screen and OpenGL setup

   auto font = loadFont(cast (char * ) "Arial.TTF");

   scope (exit) destroyFont(font);

   // draw some text

   // close OpenGL and SDL with some second delay
}

This works properly, and long is surely large enough to hold
a pointer in it, I could use sizet, I know that would be better.

My problem is that auto font here is an ulong. Could that be
wrapped into a type Font so that it only accepts assignment
from other Font type but no insecure numeric caluclations
and make the loadFont return that Font type, and other
methods use Font as arguments?