[cairo] absract_surface -> cairo_surface_t* vs void*

[Uli Schlachter]

Am 11.12.2015 um 13:34 schrieb Enrico Weigelt, metux IT consult:
> Hi folks,
> 
> 
> I've seen many places where an (abstract) surface structure is passed
> as void* pointer, which is then directly typecaste'd to the actual
> structure.
> 
> Should we change it to use cairo_surface_t* intead and then use
> container_of() for the typecast instead ?
> 
> By the way: I'd also propose an additional sanity check:
> 
> * put in an magic value (more precisely: an array of magics - for
>   deeper inheritance)

What deeper inheritance? Can surface inherit from each other at all?

>   into cairo_surface_t, so we can check individual
>   instances for correct class
> * add some macros for the typecasting and type check
> * make the whole thing (compile-time) optional

Don't the existing ->type and ->backend values serve this goal? I guess we could
add some macros for this, but ->backend == my_backend is quite obvious, I think.

Uli
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