A VALA file is linked to the Vala programming language, a statically typed, object-oriented programming language, designed to facilitate the development of GNOME-based applications. It is designed to allow modern programming techniques to be used without the additional runtime overhead imposed by languages like Python or PHP. Vala source code files are saved with the ".vala" extension.
Working with VALA Files
VALA files are primarily associated with Vala, a programming language, based on the syntax of C#, developed by GNOME specifically aimed for writing GNOME applications. Because Vala uses the GObject type system, it has first-class support for 'GTK+' and 'GNOME' application development. To open and edit VALA files, one would require a text editor or a specialized development environment such as Gedit which comes as the default text-editor of the GNOME desktop environment, or Anjuta, the GNOME Integrated Development Environment.
Compiling VALA Files
To compile VALA files into executable programs you will need the Vala compiler. Vala code is first converted to C (hence, VALA file gets translated into a .c file), which is then compiled with a C compiler, for instance, GCC. There are many tutorials available that guide you how to do it, one of which is found at GNOME - Vala Tutorial.
VALA for GNOME Application Development
Vala offers a modern, higher-level syntax and extra features such as garbage collection, asynchronous programming, and an extensive standard library, while maintaining C-level performance by compiling into C and interfacing directly with GNOME's C libraries. For developers who are interested in writing GNOME Applications, GNOME Programming Guidelines and GNOME Platform Overview can provide more insights.
VALA File Important Information
Working with VALA files can be complex for those who are unfamiliar with the Vala programming language or GObject library. Investing time in learning these tools can greatly improve one's efficiency in handling VALA files and in developing applications for the GNOME platform. There are plentiful resources available online for learning, one of them being Learn X in Y Minutes which provides a comprehensive close look at Vala.