Vala (programming language)

Vala is an object-oriented programming language with a self-hosting compiler that generates C code and uses the GObject system.

Vala
ParadigmMulti-paradigm: imperative, structured, object-oriented
DeveloperJürg Billeter, Raffaele Sandrini
First appeared2006 (2006)
Stable release
0.48.6[1] / 18 May 2020 (2020-05-18)
Typing disciplinestatic, strong
OSCross-platform all supported by GLib, but distributed as source code only.
LicenseLGPLv2.1+
Filename extensions.vala, .vapi
Websitewiki.gnome.org/Projects/Vala
Influenced by
C, C++, C#, D, Java, Boo

Vala is syntactically similar to C# and includes notable 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, wanted 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 lower-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.[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

A simple "Hello, World!" Vala program:

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 ();
    }
}

Sample code to show Vala interface with default implementation (mixin)

using GLib;

interface Printable {
	abstract string print ();
	string pretty_print (){
		return "Please " + print ();
	}
}

class NormalPrint : Object, Printable {
	override string print () {
		return "don't forget about me";
	}
}

class OverridePrint : Object, Printable {
	override string print () {
		return "Mind the gap";
	}

	override string pretty_print () {
		return "Override";
	}
}

void main (string[] args) {
	var normal = new NormalPrint ();
	var overridden = new OverridePrint ();

	print (normal.pretty_print ());
	print (overridden.pretty_print ());
}

An example using GTK to create a GUI "Hello, World!" program (see also GTK hello world):

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 GNOME 3 platforms:

valac --pkg gtk+-3.0 hellogtk.vala

See also
  • Genie, a programming language for the Vala compiler with a syntax closer to Python.
  • Shotwell, an image organiser written in Vala.
  • Geary, an email client written in Vala.
  • elementary OS, a Linux distribution with a desktop environment programmed mostly in Vala.

References
  1. "Vala - Compiler Using the GObject Type System". GNOME Project. News section. Retrieved 20 June 2020.
  2. "Vala: high-level programming with less fat". Ars Technica. Retrieved 13 December 2011.
  3. "A look at two new languages: Vala and Clojure".
  4. "Writing Multimedia Applications with Vala". Archived from the original on 28 August 2012.
Comparison with other languages
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