Re: [Vala] Creating a binding for a non-glib library and using delegate to map a function pointer

[Abderrahim Kitouni <a kitouni gmail com>]

في ح، 13-03-2011 عند 17:54 +0100 ، كتب Luca Dionisi:
> > Another important point: you shouldn't use has_target=false if the
> > library you are binding has user_data arguments, so your
> > FunctionDelegate should be defined as
> >
> > public delegate void* FunctionDelegate ();
> >
> > And generally, you should try to avoid using void* if possible. For
> > example, if it makes sense for your library, you can use a generic
> > delegate.
>
> I don't get how this would map a prototype like:
> void foobar(void *(*f)(void *), void *user_data);
We have a 'void *(*f)(void *)', it's a callback that only takes a
user_data parameter (which is implicit in vala) and returns a pointer,
at first it would be bound as:

public delegate void* FunctionDelegate ();
public void foobar (FunctionDelegate f);

then, if the type of the return value can be known "at compile time",
i.e. the delegate isn't supposed to return a random pointer, you can
convert this to generics using something like (untested):

public delegate G FunctionDelegate<G> ();
public void foobar<G> (FunctionDelegate<G> f);


> To be explicit in real world, I want to make a binding for GNU Pth. In
> their header there is:
>
> extern pth_t          pth_spawn(pth_attr_t, void *(*)(void *), void *);
It's better to look at their documentation rather than their header :-)
Otherwise, I think what I said above applies.

You can also take a look at how this is done in the GLib threading API
for inspiration ;-)
http://git.gnome.org/browse/vala/tree/vapi/glib-2.0.vapi#n1777

HTH,
Abderrahim