Vala (programming language)

Vala

Paradigm	Multi-paradigm: imperative, structured, object-oriented
Developer	Jürg Billeter, Raffaele Sandrini
First appeared	2006 (2006)
Stable release	0.32.0 / 21 March 2016 (2016-03-21)
Typing discipline	static, strong
OS	Cross-platform all supported by GLib, but distributed as source code only.
License	LGPL 2.1+
Filename extensions	.vala, .vapi
Website	wiki.gnome.org/Projects/Vala
Influenced by
C, C++, C#, D, Java

Vala is an object-oriented programming language with a self-hosting compiler that generates C code and uses the GObject system (that "can be seen as an alternative to C-derived languages such as C++ and Objective-C").

Vala is syntactically similar to C# and includes several features such as: anonymous functions, signals, properties, generics, assisted memory management, exception handling, type inference, and foreach statements. Its developers Jürg Billeter and Raffaele Sandrini aim to bring these features to the plain C runtime with little overhead and no special runtime support by targeting the GObject object system. Rather than compiling directly to machine code or assembly language, it compiles to a higher level intermediate language. It source-to-source compiles to C, which is then compiled with a C compiler for a given platform, such as GCC.

For memory management, the GObject system provides reference counting. In C, a programmer must manually manage adding and removing references, but in Vala, managing such reference counts is automated if a programmer uses the language's built-in reference types rather than plain pointers.

Using functionality from native code libraries requires writing vapi files, defining the library interfacing. Writing these interface definitions is well-documented for C libraries, especially when based on GObject. However, C++ libraries are not supported. Vapi files are provided for a large portion of the GNOME platform, including GTK+.

Vala was conceived by Jürg Billeter and was implemented by him and Raffaele Sandrini, finishing a self-hosting compiler in May 2006.

Code example

A simple "Hello, World!" vala program (see also GTK+ hello world)

void main () {
    print ("Hello World\n");
}

A more complex version, showing some of Vala's object-oriented features:

class Sample : Object {
    void greeting () {
        stdout.printf ("Hello World\n");
    }
    
    static void main (string[] args) {
        var sample = new Sample ();
        sample.greeting ();
    }
}

An example using GTK+ to create a GUI "Hello, World!" program:

using Gtk;

int main (string[] args) {
    Gtk.init (ref args);
    
    var window = new Window ();
    window.title = "Hello, World!";
    window.border_width = 10;
    window.window_position = WindowPosition.CENTER;
    window.set_default_size (350, 70);
    window.destroy.connect (Gtk.main_quit);
    
    var label = new Label ("Hello, World!");
    
    window.add (label);
    window.show_all ();
    
    Gtk.main ();
    return 0;
}

The last example needs an extra parameter to compile on GNOME3 platforms:

valac --pkg gtk+-3.0 hellogtk.vala

This is the converted C code:

/* hellogtk.c generated by valac 0.28.0, the Vala compiler
 * generated from hellogtk.vala, do not modify */

#include <glib.h>
#include <glib-object.h>
#include <stdlib.h>
#include <string.h>
#include <gtk/gtk.h>

#define _g_object_unref0(var) ((var == NULL) ? NULL : (var = (g_object_unref (var), NULL)))

gint _vala_main (gchar** args, int args_length1);
static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self);

static void _gtk_main_quit_gtk_widget_destroy (GtkWidget* _sender, gpointer self) {
	gtk_main_quit ();
}

gint _vala_main (gchar** args, int args_length1) {
	gint result = 0;
	GtkWindow* window = NULL;
	GtkWindow* _tmp0_ = NULL;
	GtkLabel* label = NULL;
	GtkLabel* _tmp1_ = NULL;
	gtk_init (&args_length1, &args);
	_tmp0_ = (GtkWindow*) gtk_window_new (GTK_WINDOW_TOPLEVEL);
	g_object_ref_sink (_tmp0_);
	window = _tmp0_;
	gtk_window_set_title (window, "Hello, World!");
	gtk_container_set_border_width ((GtkContainer*) window, (guint) 10);
	g_object_set (window, "window-position", GTK_WIN_POS_CENTER, NULL);
	gtk_window_set_default_size (window, 350, 70);
	g_signal_connect ((GtkWidget*) window, "destroy", (GCallback) _gtk_main_quit_gtk_widget_destroy, NULL);
	_tmp1_ = (GtkLabel*) gtk_label_new ("Hello, World!");
	g_object_ref_sink (_tmp1_);
	label = _tmp1_;
	gtk_container_add ((GtkContainer*) window, (GtkWidget*) label);
	gtk_widget_show_all ((GtkWidget*) window);
	gtk_main ();
	result = 0;
	_g_object_unref0 (label);
	_g_object_unref0 (window);
	return result;
}

int main (int argc, char ** argv) {
#if !GLIB_CHECK_VERSION (2,35,0)
	g_type_init ();
#endif
	return _vala_main (argv, argc);
}

IDE support

There are various projects in various states of stability in order to provide IDE support for Vala:

• Anjuta
• Github's Atom (text editor) (With the Vala package installed).
• GNOME Builder
• Emacs
• Euclide
• Geany
• MonoDevelop
• NetBeans
• RedCar
• Scratch (elementary OS)
• Sublime Text (syntax plugin)
• TextMate
• Vala Toys for Gedit
• Val(a)IDE (itself written in Vala, discontinued)
• Valable, a Vala plug-in for Eclipse.
• Valama
• Valencia
• Vim (syntax plugin)

See also

• Genie, a programming language for the Vala compiler with a syntax closer to Python
• Shotwell, an image organiser written in Vala
• Ease, a presentation program written in Vala
• elementary OS, a Linux distribution with a desktop environment programmed mostly in Vala

External links

• Official website, on GNOME Live!
• ValaToWindows, Vala compiled binaries for Windows
• LibGee, a collection library for vala.
• API Documentation
• Vala sample code for beginners
• List of Vala programs
• web-vala, a simple web application framework for Vala

Comparison with other languages

• Vala and Java
• Vala and C#
• Benchmark of Vala versus C# and C
• More Vala benchmarks