Vala (programming language)

Vala

Paradigm	Multi-paradigm: imperative, structured, object-oriented
Developer	Jürg Billeter, Raffaele Sandrini
First appeared	2006
Stable release	0.50.2[1] / 19 November 2020
Preview release	0.49.92 / 4 September 2020
Typing discipline	static, strong
OS	Cross-platform all supported by GLib, but distributed as source code only.
License	LGPLv2.1+
Filename extensions	.vala, .vapi
Website	wiki.gnome.org/Projects/Vala
Influenced by
C, C++, C#, D, Java, Boo

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 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 { public abstract string print ; public virtual string pretty_print  { return "Please " + print ; } } class NormalPrint: Object, Printable { string print  { return "don't forget about me"; } } class OverridePrint: Object, Printable { string print  { return "Mind the gap"; } public 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

External links

• Official website
• 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
• Autovala, a program that automatizes and simplifies creating CMake and Meson files for Vala/C projects
• VLS, Vala Language Server Protocol implementation in Vala
• GVLS, Another Vala Language Server Protocol implementation in Vala
• The Vala community on GitHub

Comparison with other languages

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