Re: [Vala] Vala base classes

[Jürg Billeter <j bitron ch>]

Hi Matt,

On Fri, 2007-12-07 at 09:20 -0500, Matt Brown wrote:
> I wanted to tell how awesome this project is (as if you didn't know).  
> It is one of those ideas
> that is so elegant it makes me a little jealous.  It's always annoyed me 
> that separate, distinct concepts
> like clean OO syntax and runtime engines are usually welded together as 
> if they required one another.
> Thanks for Vala, I really hope the project grows to realize it's 
> incredible potential.

Thanks!

> Why can't class inheritance from Glib.Object be implicit instead of 
> explicit?
>
> So Vala uses GObject to implement classes.  Why does a programmer need 
> to know that
> internal implementation detail?
>
> Is there a strong need for classes that do not inherit from GObject?
> these are just mapped to structs, and structs are already available in 
> the language, right?

While most classes (should) derive from GObject, it's not always the
case. For one there are many libraries that don't use GObject at all or
don't use GObject for all class types and we want to be able to use such
libraries from Vala. Examples include GLib itself, cairo, libxml2, and
many more. 

There are also some rare cases where you want to define non-GObject in
Vala, either for performance reasons (when you need to create hundred
thousands of instances in short time) or if you need more control about
the field layout. You can also define new foundation types in Vala by
deriving from GLib.TypeInstance, such types can be used as lightweight
objects, that's what GStreamer does with GstMiniObject.

The difference between structs and classes in Vala is that structs are
value-types and classes are reference-types, as documented in the
reference manual[1]. That's the same as in C#.

In previous versions of Vala all classes derived from GObject; there was
an attribute to mark a struct as a (non-GObject) reference type. However
it was very confusing that some structs were value-types and other
structs were reference-types. While the current solution requires you to
type an extra ": Object" from time to time (compare that to the C
boilerplate), the approach makes a lot more sense, in my opinion.

Jürg

[1] http://www.vala-project.org/doc/vala/types.html