Re: [Vala] Generating bindings for non-GLib/GObject based API

[Jan Hudec <bulb ucw cz>]

On Fri, Apr 23, 2010 at 09:36:18 +0200, Michael Wild wrote:
> Another thing where I'm not sure how to best solve it: The basic C-type I'm
> using is a typedef to a pointer whose base-type is implementation dependent
> (i.e. unknown). E.g. like this:
>
> typedef struct unknown_type* Thing;
>
> Now, in my small test cases, I used the following for the binding:
>
> [SimpleType]
> [CCode (cname = "Thing", cheader_filename = "thing.h", free_function = "free")]
> struct Thing {
>   [CCode (cname = "create_thing")]
>   private static int create_imp(Thing* self, int a, int b, double c); 
>   [CCode (cname = "create_thing_wrapper")]
>   public static Thing create(int a, int b, double c) {
>     Thing self;
>     int stat = create_imp(&self, a, b, c); 
>     return self;
>   }
>   
>   [CCode (cname = "print_thing")]
>   public void print();
> }
>
> This compiles and runs, but Vala now (quite understandably) thinks that
> Thing is a value-type and doesn't call free() on it. AFAIK for this to
> happen I'd need to change Thing to be a of compact class type, but then
> everything else would break because Vala starts passing the object around
> as a pointer (i.e. resulting in unknonw_type**, where unknown_type* is
> expected).

Actually I believe

    [Compact]
    [CCode (cname = "void", ...)]
    class Thing ...

should work. It will give you void * passed around, so it's some kind of
pointer and C implicitly casts to and from void *, so no errors and no
warnings.

You can also just make it

    [Compact]
    [CCode (cname = "struct unknown_type", ...)]
    class Thing ...

with the real value for "unknown_type" from the library header. That will
make the code more type-safe on the C side, but vala will check the types
enough and it would be relying on something not officially documented.

You may also need to set the [CCode(copy_function=...)] or explicitly tell
vala that it can't be copied via [CCode(has_copy_function=false)].

On a side note, structs normally have destroy_function rather than
free_function, but I am not sure there is a difference.

-- 
                                                 Jan 'Bulb' Hudec <bulb ucw cz>