Re: [Vala] this = Object

[Cyrille Colin <colin univ-metz fr>]

hi jim ... and thank you !

you've explained clearly what I missed. I now remove the init function
and retrieve the (void* user_data) when i pass the callback. it's well
done automatically by vala. thanks again.

Cyrille.

Le mardi 28 septembre 2010 à 11:55 -0700, Jim Nelson a écrit :
> If you're trying to use a delegate from C, you need to be aware of the
> delegate's target, which is a hidden parameter to Vala code but
> visible in C.
>
> If you compile your code with the --save-temps flag enabled, you can
> see how a delegate is constructed in C.  For example:
>
> delegate void Callback(int32 i);
>
> Becomes this in the .c:
>
> typedef void (*Callback) (gint32 i, void* user_data);
>
> The user_data is the target (in Vala-parlance).  Your C code should
> invoke the callback like this:
>
> Callback _cb = cb;
> ...
> _cb (i, obj);
>
> Rob's right, you can't (or shouldn't) assign to "this" in Vala.  When
> you invoke the callback with obj as the user_data, Vala's internal
> code will use it as the "this" reference.
>
> A useful reference if you're making a VAPI:
> http://live.gnome.org/Vala/Bindings/MetadataFormat
>
> -- Jim
>
> On Tue, Sep 28, 2010 at 5:10 AM, Cyrille Colin <colin univ-metz fr>
> wrote:
>         hi,
>         i've just update to 0.10 from 0.8.1 and I guess now vala
>         detect one of
>         my bad.
>         I used a init function to give my object pointer to external
>         function
>         that will manage callback :
>         
>                init(this)
>         
>         init() is define in a vapi :
>         public static void init (ValaObj obj);
>         
>         and use in External library like this :
>         
>         static void *ValaObj;
>         void init (void *obj) {
>                ValaObj = obj;
>         }
>         
>         Then i define in vapi the callback, C -> Vala :
>         public delegate uint32 callback ( ValaObj, int value);
>         
>         and this is my callback in Vala code:
>         public uint32 cb (ValaObj obj, int value) {
>                        this = obj;
>         ...
>         }
>         it works fine with 0.8.1 and throw exception with 0.10 :
>         error: unsupported lvalue in assignment
>         May someone could help me,
>         thanks in advance,
>         Cyrille.
>         
>         
>         
>         
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