On 23. Apr, 2010, at 22:29 , Jan Hudec wrote:
> 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.
I don't think that I'd like that one particularly... I'd rather prefer to use a
Vala wrapper class then.
>
> 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.
Unfortunately that's impossible. The official standard states that there is a
opaque type Thing, but nothing more. Every implementor is free to do as he
pleases... Some even typedef it to an integer handle.
>
> 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.
Noted.
Michael
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