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Vala is a high-level, object-oriented programming language with a self-hosting compiler that generates C code and uses the GObject system. Developed by Jürg Billeter and Raffaele Sandrini, it was designed to bring modern programming language features to GNOME developers without imposing any additional runtime requirements and without using a different ABI compared to applications and libraries written in C. Vala includes features such as interfaces, properties, signals, and generics which are not typically found in C. It also has additional features like lambda expressions, exception handling, type inference, and asynchronous programming. Despite its syntactical similarity to C#, it does not include garbage collection, instead using deterministic memory management (reference counting). Vala's compiler, valac, is written in Vala itself and compiles the code into C, making it relatively easy to use in combination with existing libraries written in C. The output of valac compilation is a C source and header file that can be compiled with a platform's standard C compiler. Vala is mainly used for developing GNOME applications but can be used for any software that uses the GObject system.

Ask the right questions secure the right Vala talent among an increasingly shrinking pool of talent.

First 20 minutes

General Vala app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Vala application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What are the basic data types in Vala?

The basic data types in Vala are int, float, double, bool, string, and char.

How would you declare an array in Vala?

You can declare an array in Vala using the following syntax: type[] arrayName = new type[size]; For example, int[] numbers = new int[5];

What is the purpose of the 'using' keyword in Vala?

The 'using' keyword in Vala is used to include namespaces in the program. It allows the programmer to use classes, methods, and other members of the namespace directly without specifying the full namespace path.

How would you handle exceptions in Vala?

In Vala, exceptions are handled using try, catch, and finally blocks. The code that might throw an exception is placed inside the try block. If an exception is thrown, it's caught in the catch block. The finally block contains code that is always executed, regardless of whether an exception was thrown or not.

What are signals in Vala and how would you use them?

Signals in Vala are a way of delivering notifications to interested parties about certain events. They are used in event-driven programming. You can connect a signal to a method so that the method is called whenever the signal is emitted.

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What you’re looking for early on

Has the candidate demonstrated a strong understanding of the Vala programming language?

Does the candidate show a good problem-solving ability?

How well does the candidate understand Object-Oriented Programming (OOP)?

Can the candidate articulate their thoughts clearly and effectively?

Next 20 minutes

Specific Vala development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

Describe the difference between structs and classes in Vala.

Structs in Vala are value types and are passed by value, while classes are reference types and are passed by reference. Structs do not support inheritance or virtual methods, but classes do.

How would you implement multithreading in Vala?

Multithreading in Vala can be implemented using the Thread class. You can create a new thread by calling the Thread.create() method and passing in the method that should be run in the new thread.

What are lambda expressions in Vala and how would you use them?

Lambda expressions in Vala are anonymous functions that can be used to create delegates or expression tree types. They can be used in any context that requires a delegate type.

Describe the difference between synchronous and asynchronous methods in Vala.

Synchronous methods in Vala block the execution of the program until they complete, while asynchronous methods do not block the execution and allow the program to continue with other tasks. Asynchronous methods are marked with the 'async' keyword and usually return a 'GLib.Future' object.

How would you use the 'yield' keyword in Vala?

The 'yield' keyword in Vala is used in asynchronous methods to pause the execution of the method and return control to the caller. When the asynchronous operation that the method is waiting for completes, the method resumes execution from where it left off.

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At this point, a skilled Vala engineer should demonstrate strong problem-solving abilities, proficiency in Vala programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Vala.

What does the following Vala code do?
public int add(int a, int b) {
  return a + b;
}
This code defines a function named 'add' that takes two integers as parameters and returns their sum.
What will be the output of the following Vala code snippet?
string str = "Hello, World!";
print("%s\n", str);
The output of this code will be 'Hello, World!' printed to the console.
What does the following Vala code do?
int[] arr = {1, 2, 3, 4, 5};
foreach (var i in arr) {
  print("%d\n", i);
}
This code creates an integer array and then iterates over each element in the array, printing each element to the console.
What does the following Vala code do?
void thread_func() {
  print("Hello from thread!\n");
}

Thread.create(thread_func, false);
This code creates a new thread that executes the function 'thread_func', which prints 'Hello from thread!' to the console.

Wrap-up questions

Final candidate for Vala Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Vala application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What is the purpose of the 'base' keyword in Vala?

The 'base' keyword in Vala is used to refer to the base class from a derived class. It can be used to call methods or access properties of the base class.

How would you implement a singleton pattern in Vala?

A singleton pattern in Vala can be implemented by creating a class with a private constructor and a static method that returns the single instance of the class. The instance is stored in a private static field of the class.

What is the difference between '==' and '===' in Vala?

'==' in Vala is used for value comparison, it checks if the values of two operands are equal or not. '===' on the other hand, is used for reference comparison, it checks if two reference variables refer to the same object or not.

Vala application related

Product Perfect's Vala development capabilities

Beyond hiring for your Vala engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Vala projects, and can engage in multiple capacities.

Vala Consultive assessments

Vala Application Conversion Assessment Vala Application Integration Assessment Vala Data & Database Integration Assessment

Custom Vala development projects

Custom Vala App Conversion Vala Custom App Development Process App UI Design for Vala Facelifts

Hiring guide for Vala Engineers

Vala Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the Vala engineer at this point.

Vala Consultive assessments

Custom Vala development projects