Closures

While Vala has lambda expressions for a long time, they haven’t supported accessing local variables from the outer method. With the release of Vala 0.7.6 this has changed, and you can access and set any local variable from lambda expressions. One place where I’d expect this to be convenient is in signal handlers:

void main (string[] args) {
    Gtk.init (ref args);
 
    var window = new Gtk.Window (Gtk.WindowType.TOPLEVEL);
    window.set_default_size (300, 50);
    window.destroy.connect (Gtk.main_quit);
 
    var button = new Gtk.Button.with_label ("Click me!");
    button.clicked.connect (() => {
        window.title = "Closures in Vala";
    });
 
    window.add (button);
    window.show_all ();
 
    Gtk.main ();
}

You can even write recursive lambda expressions:

delegate int Func (int i);
 
void main () {
	Func fib = null;
	fib = (i) => (i <= 1) ? i : (fib (i - 2) + fib (i - 1));
 
	for (int i = 0; i < 10; i++) {
		message ("%d", fib (i));
	}
}

Asynchronous methods

The idea of integrating async methods into the language is to make it easier to write code that calls or implements async methods. Async methods are frequently used in I/O API such as GIO and in D-Bus clients and servers. Traditionally, writing async code has beeen quite painful as you often end up writing callback chains and completely lose track over the control flow in the process.

Experimental support for async methods has been implemented in Vala almost a year ago. However, the implementation was rather a proof of concept than a finished solution. While I still expect a few bugs in that area with 0.7.6, it’s a lot more robust and complete than it used to be a short time ago.

So how does it look like? It’s not unlike Alex’s AsyncRunner in JavaScript except that it’s even more concise as it’s fully integrated into the language. The following code defines an async method list_dir that asynchronously enumerates all files in the home directory:

async void list_dir () {
    var dir = File.new_for_path (Environment.get_home_dir ());
    try {
        var e = yield dir.enumerate_children_async (FILE_ATTRIBUTE_STANDARD_NAME, 0, Priority.DEFAULT, null);
        while (true) {
            var files = yield e.next_files_async (10, Priority.DEFAULT, null);
            if (files == null) {
                break;
            }
            foreach (var info in files) {
                print ("%s\n", info.get_name ());
            }
        }
    } catch (GLib.Error err) {
        warning ("Error: %s\n", err.message);
    }
}
 
void main () {
    list_dir.begin ();
 
    var loop = new GLib.MainLoop (null, false);
    loop.run();
}

As you can see, it’s very easy to call the async methods enumerate_children_async and next_files_async in try-catch blocks and loops. There is no need for manually creating structs for user_data or similar inconveniences.

Async methods in Vala can also be used to implement D-Bus servers that can process multiple requests at the same time. Using it couldn’t be easier, just write an async method such as the above example, add it to a class annotated with [DBus (name = "org.example.Test")], and register an instance of that class with the D-Bus connection. Vala also supports async methods on client-side D-Bus interfaces.

• D-Bus server support has been rewritten to directly use libdbus. Avoiding dbus-glib marshalling helps Vala to support complex D-Bus types more easily.
• All Vala structs will now be registered with GBoxed.
• Many critical warnings and crashes on invalid code have been fixed and replaced by better understandable error messages.
• Private class fields and class destructors (base_finalize) are now supported.
• vala-gen-project has been dropped from the package, it is now part of Vala Toys for gEdit, which is progressing very well.
• Many bug fixes all over the place.

In the following weeks and months we will focus on bug fixing, finishing some partially implemented features, and switching to GObject Introspection trunk for our bindings. We’re aiming to release a stable Vala 1.0 in March 2009.

• Support for overriding default method handlers of signals.
  See custom GTK+ Widget example
• Improvements to D-Bus service support
• Parser for Genie
• Documentation and binding updates
• Many bug fixes and performance improvements

Thanks a lot to all the people helping out and have fun with the new version! For the following two releases we will focus on GObject introspection hacking to make it easy to write great bindings for many languages.

• Non-null types are enabled by default
• Experimental support for writing D-Bus services
• New handwritten parser
• Don’t require `new’ operator for structs
  var color = Color (0×00, 0×88, 0xee);
• Many bug fixes and binding updates

• Enhanced property syntax
  public int foo { get; private set; default (3); }
• New errordomain syntax
  public errordomain MyError { NOT_FOUND, TIMED_OUT }
• Detect missing return and break statements and unreachable code
• Improved pointer support (pointer member access, pointer element access, and pointer arithmetic)
• New bindings: WebKit, JSON-GLib, goocanvas, hildon-fm-2, taglib, libusb, and bzip2
• A lot of bug fixes

It generates the necessary autotools magic for a Vala console or GTK+ application including i18n support and it passes distcheck. Suggestions for improvements are more than welcome.

We’ve also replaced the bindings generator gidlgen by vala-gen-introspect which includes a real C parser instead of Perl scripts using regular expressions. The 20 included bindings have all been ported. Some smaller features and many bug fixes can also be found in the new release.

There are two articles about Vala and an interview in the German Linux-Magazin, all by Christian Meyer.

• Object initializers
  var btn = new Button () { label = “Button” };
• Creation methods in structs
• Experimental support for new fundamental classed types
  class MiniObject : TypeInstance { … }
• [Notify] attribute for properties

A noteworthy change is that the type system has been made more consistent by converting the reference-type structs in the bindings to classes. The [ReferenceType] attribute is gone, you can now declare all reference types as classes in bindings, even if they don’t derive from GObject. A side-effect of this change is that you now always have to specify the base class in your class declarations, e.g. use

using GLib;
public class Bar : Object { … }

to declare a class Bar which derives from GObject. The advantage is that you can be sure now that all structs have value-type semantics and all classes have reference-type semantics, no mixup anymore.