Re: [Vala] First questions

[Juerg Billeter <j bitron ch>]

Hi Zsombor

On Sam, 2006-07-29 at 12:41 +0200, Zsombor wrote:
>  Nice language, it looks very interesting ! I've tried to create with it
> a simple program, but I found some problem/question.

Thanks for testing.

>  First, how the memory is managed? I suspect there is no garbage
> collector. If it's true how can I release the objects? Ass I see no
> explicit 'release' operation in the test programs.

Vala uses reference counting to manage memory of GObject instances. You
don't need to explicitly use g_object_ref / g_object_unref, though, as
the Vala compiler automatically inserts appropriate statements if you
correctly declare your fields and variables.

In Vala each field and each local variable - pointing to an object - is
either a strong or a weak reference. Strong reference variables work
automatically call g_object_ref and/or g_object_unref on assignments.
Weak references are necessary to get around the garbage cycle problem
that arises with reference counting - and they may improve performance.

Fields default to strong references while local variables default to
weak references to avoid the reference counting overhead.

To declare a field as a weak reference, you have to prepend the keyword
`weak' to the field type. To declare a local variable as a strong
reference, you have to prepend the keyword `ref' to the variable type.

Methods may transfer ownership of the return value to the caller. If
they do, you have to prepend the keyword `ref' to the return type to get
memory management right. If you assign the return value of a method that
transfers ownership to a local variable that is a weak reference, the
local variable automatically becomes a strong reference as a weak
reference wouldn't be allowed there.

This may sound a bit complicated compared to languages with integrated
garbage collector, it's quite simple, though, when you get used to it.

>  The second, more practical question of mine is how to specify to
> include Gtk? I wrote a simple program: 
>
> using GLib;
> using Gtk;
>
> class HelloWorld {
>
>       static int main (int argc, string[] argv) {
>               var w = new Window();
>               return 0;
>       }
>
> }
>
> But I cant compile it with valac. No matter how I specify :
> valac --vapidir=../vapi/ --pkg=Gtk --library=gtk-2.0.vala gtktest.vala
>
> What's the expected format of --pkg=? and --library=? declarations? 

I've named the VAPI files like the corresponding pkg-config files, so
you have to use `--pkg=gtk+-2.0'. BTW: You only need to use --library if
you write a library, not if you use one; I will hopefully document all
this sometime soon. The GTK+ binding hasn't been shipped with the vala
0.0.1 tarball but you can get it from SVN. I also plan to release vala
0.0.2 relatively soon which will include the still incomplete GTK+
binding.

Don't hesitate to ask further questions, I know that the documentation
is missing.

Regards,

Jürg
-- 
Juerg Billeter <j bitron ch>