Re: [Vala] Problem with references

[Dominique Würtz <housirer gmx de>]

Jürg Billeter schrieb:
> Hi Dominique,
>
> On Fre, 2006-08-25 at 10:10 +0200, Dominique Würtz wrote:
>   
> > First of all, thank you for resolving all those issues so quickly.
> >     
>
> Anytime, thanks for pointing out important issues.
>
>   
> > Now for my bindings, I need to pass references around (references to 
> > Cairo.Matrix). I tried to use the ref keyword like this
> >
> > class X {
> >     public ref Cairo.Matrix transform;
> >
> >     public ref Cairo.Matrix get_transform ()
> >     {
> >         return transform;
> >     }
> > }
> >
> > in the belief "ref Cairo.Matrix" would translate to "cairo_matrix_t *". 
> > However, the ref attribute seems to have no effect on the generated code.
> >     
>
> Vala mostly follows C#'s model of value- and reference-type semantics
> with the exception that Vala allows to mark structs as reference-type to
> better integrate with non-GObject based C libraries. Cairo.Matrix is
> currently declared as a normal value-type struct which means that the
> only place you can pass a reference is in a method parameter. Return
> types can't be declared as `ref' for that purpose and the compiler
> should have reported an error.
>
> In that concrete case it would probably be best to just mark
> Cairo.Matrix as a reference-type, so it will always be passed by
> reference. That would make it impossible to ever pass it by value,
> though. Do you see a problem with that or shall I change Cairo.Matrix as
> afore said?
>
>   
No, I didn't find any API which requires passing by value so it should 
be ok, however, there should be the possibility to make a copy of the 
struct. Maybe a default copy constructor for ref types a la

Cairo.Matrix a;
Cairo.Matrix b = new Cairo.Matrix(b);

would be the way to go?
> > BTW, I had to add
> >
> > [CCode (cname = "cairo_matrix_t")]
> >
> > to cairo.vala in order to have Vala use the proper name of the cairo struct.
> >     
>
> Right, fixed that here, thanks.
>
> Regards,
>
> Jürg
>
>
>