Vala (programming language)

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Vala
Paradigm(s) Multi-paradigm: imperative, structured, object-oriented
Developer Jürg Billeter, Raffaele Sandrini
Appeared in 2006
Stable release 0.23.3[1] / 18 February 2014; 2 months ago (2014-02-18)
Typing discipline static, strong
Influenced by C, C++, C#, D, Java, Python
OS cross-platform all supported by GLib, but distributed as source code only.
License LGPL 2.1+
Filename extension(s) .vala, .vapi
Website live.gnome.org/Vala

Vala is an object-oriented programming language with a self-hosting compiler that generates C code and uses the GObject system. 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.[2] 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 being compiled directly to assembly or to another intermediate language, Vala is source-to-source compiled to C which is then compiled with a platform's standard C compiler, such as gcc.[3]

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.[4]

Code example[edit]

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

int main () {
    print ("Hello World\n");
 
    return 0;
}

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 0.22.0, 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) {
	g_type_init ();
	return _vala_main (argv, argc);
}

IDE support[edit]

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

See also[edit]

  • Genie, a programming language for the Vala compiler with a syntax closer to Python
  • MonoDevelop, a programming IDE that runs on Linux, Windows and Mac OS X[7] with support for Vala
  • 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

References[edit]

External links[edit]

Comparison with other languages