RE: [AD] Why aren't BITMAP * parameters const where appropriate?

[Elias Pschernig <elias@xxxxxxxxxx>]

> Arguably, Allegro should have const-cast'ed away the const for those 
> cases where the bitmap is logically const.

I wonder if casting away const wouldn't cause subtle side-effects in
some special cases though.

void test(BITMAP const a) {
    BITMAP b = a;
    c = getpixel(a,...);
    b = a;
    ... use b now ...

If the first parameter to getpixel is const, I guess, the optimizer
could just discard the second b = a, since it knows that a has not
changed (don't know though, but it always was my explanation why const
is useful). Of course, you can never use a BITMAP not created with
create_bitmap, so this is not a real example.

If it is safe to cast it away, I guess we could use const everywhere
where it makes sense. And else, things like get_bitmap_color_depth()
really could have a const parameter. Actually, all functions which don't
modify anything, and don't call a vtable function.

-- 
Elias Pschernig