Re: Dodgy function pointer casts

On 2007-04-26, Ben Hutchings <ben-/[email protected]> wrote:
>> Umm... any kind of OO shit in C absolutely positively depends on
>> function pointer casts.
>
> I haven't noticed this being necessary in the GObject system.  It does
> rely on data pointer casts, but those are fine.

G-shit just hides casts in A_ZILLION_AWFUL_MACROS_WITH_UNMANAGEABLE_NAMES.

Anyway, the _FooClass structures contain function pointers for the 
pseudo-dynamic functions. The first parameter is of type Foo*. A 
subclass Bar must fill these in. Obviously in the subclass's 
implementation of these functions, the first parameter is Bar*. 
Ion's _much_ more usable object system, on the other hand, uses 
a table of mappings {dynfun, implementation}, so that it isn't 
necessary to fill in complex hierarchies of structures: you just
list the functions that you do implement. It actually needs
_less_ explicit casts than the G-shit, because the function 
pointers in the structure are of type void (*)(), which any
function 'returning' void can be implicitly cast to. Functions
that do not return a void, need (DynFun*) explicit casts, however.
Cast of 'void (*)(Bar*)' to 'void (*)(Foo*)' must always be explicit.

-- 
Tuomo