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

[Michael Wild <themiwi users sourceforge net>]

On 22. Apr, 2010, at 15:48 , Abderrahim Kitouni wrote:

> Hi,
>
> 2010/4/22 Michael Wild <themiwi users sourceforge net>:
> > Hi all
> >
> > I am currently trying to generate bindings for a API which has some
> > peculiarities which I can't seem to find any solution for.
> >
> > 1) Constructor function: Say I would like to use a C function as the constructor for a class (as e.g. 
> > newwin is used in curses.vapi). However, that C function does not return the allocated and initialized 
> > object in the return value, but as the first argument. The return value is an error code instead. How 
> > would I handle this?
> I don't understand this, does the function still alocate the instance,
> or does it just initialize it?

It does both, it just doesn't return the result in the return argument, but in one of the parameters. I found 
an example with the same issue, but I don't understand how Vala can be doing the right thing. Looking at 
zlib.vapi I see

[CCode (cname = "z_stream", destroy_function = "deflateEnd")]
public struct DeflateStream : Stream {
    [CCode (cname = "deflateInit")]
    public DeflateStream (int level = Level.DEFAULT_COMPRESSION);
    // ...
}

but deflateInit has the following (sanitized) signature:

int deflateInit(z_stream *strm, int level);

How does Vala know that it must pick the first argument and not the return value?


> > 2) Delegates: The C API defines a number of callback functions, most of which take some user-defined data 
> > as an argument one registers along with the callback function. However, the user data is often neither the 
> > first nor the last argument. How can I wrap this?
> [CCode (instance_pos=)]
> you can use things like 3.1 for "after the 3rd argument" and 3.9 for
> "before the 4th argument"

Cool, just what I need (I hope the semantics given in below reference are still valid)...

> > 3) Is there any comprehensive attributes reference somewhere? The Vala reference (draft version) doesn't 
> > really say much, and actually seems to be quite a bit stale.
>
> Some time ago, someone posted a "work in progress" here [1], not sure
> if it has been added to the wiki or something.

Certainly very valuable information (and IMHO hard to find...)

> Regards,
> Abderrahim
>
> [1] http://mail.gnome.org/archives/vala-list/2009-December/msg00019.html


Thanks a lot!

Michael