Well, you don't really need to mimic OO to make that code cleaner and less error prone. Here's what he wrote in order to complain about it: if (mode == am

Well, you don't really need to mimic OO to make that code cleaner and less error prone. Here's what he wrote in order to complain about it: if (mode == ambient) { // handle pixels as ambient... int steps = right.a.x - left.a.x; float dv = (right.a.ambientLight - left.a.ambientLight)/steps; float currentIntensity = left.a.ambientLight; for (i=left.a.x; i<right.a.x; i++) { WorkOnPixelAmbient(i, dv); currentIntensity+=dv; } } else if (mode == gouraud) { // handle pixels as gouraud... int steps = right.g.x - left.a.x; float dred = (right.g.red - left.g.red)/steps; float dgreen = (right.g.green - left.g.green)/steps; float dblue = (right.g.blue - left.g.blue)/steps; float currentRed = left.g.red; float currentGreen = left.g.green; float currentBlue = left.g.blue; for (j=left.g.x; i<right.g.x; j++) { WorkOnPixelGouraud(j, currentRed, currentBlue, currentGreen); currentRed+=dred; currentGreen+=dgreen; currentBlue+=dblue; } Nobody should do that. We use a temporary variable of the correct type. For example this way (but it could also be done with pointers to access directly the union variable): switch(mode) { case AMBIENT: { PixelDataAmbient l = left.a; PixelDataAmbient r = right.a; int steps = r.x - l.x; float dv = (r.ambientLight - l.ambientLight)/steps; /* ... */ break; } case GOURAUD: { PixelDataGouraud l = left.g; PixelDataGouraud r = right.g; int steps = r.x - l.x; /* ... */ break; } /* ... */ default: show_error("Illegal mode"); } There is no need to cart all the .a. and .g. around and clutter the code. And there is no possibility to accidentally access the wrong fields the wrong way: trying to access l.ambientLight in the second block (GOURAUD) will fail at compilation since a PixelDataGouraud doesn't have an ambientLight field. It is also not possible to do PixelDataGouraud l = left.a; since left.a is not a PixelDataGouraud. Much cleaner, much more readable and avoids most of the possible errors he complains about.