Hiring guide for Scala Engineers

Scala Developer Hiring Guide

Scala is a high-level, general-purpose programming language that combines object-oriented and functional programming paradigms. It was developed in the early 2000s by Martin Odersky and his team at EPFL, Switzerland. Scala stands for "Scalable Language," reflecting its design to grow with the demands of its users. The language runs on Java Virtual Machine (JVM) and is fully interoperable with Java, meaning it can use any code written in Java. This makes it an attractive choice for developers who want to transition from Java or work on projects where they need both languages. Scala introduces several innovative features such as type inference, pattern matching, mixins and string interpolation among others. It also supports higher-order functions which make it easier to write concise code. In addition to being used for web development purposes like creating APIs or building microservices architecture applications using frameworks like Play Framework or Akka HTTP server toolkit; Scala is also popularly used in data analysis tasks due to libraries like Apache Spark which are written in Scala itself. Overall, despite having a steeper learning curve compared to some other languages due its complex syntax; once mastered - programmers find that writing programs becomes more efficient because of how expressive this language can be while still maintaining strong static typing system ensuring safety & robustness of your software application's codebase at compile-time itself before even running them live onto production servers thereby reducing chances of runtime errors significantly!

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

First 20 minutes

General Scala app knowledge and experience

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

What are the key features of Scala?
Scala is object-oriented, functional, statically typed, extensible, and it has a sophisticated type inference system. It also supports higher-order functions, currying, pattern matching, and many other advanced features.
How would you define a variable in Scala?
You can define a variable using the 'var' keyword for mutable variables and 'val' keyword for immutable variables. For example, 'var x = 10' or 'val y = 20'.
What is the difference between 'var' and 'val' in Scala?
'var' is used to declare a mutable variable, which means the variable's value can be changed. 'val' is used to declare an immutable variable, meaning once a value is assigned, it cannot be changed.
What is a case class in Scala?
A case class is like a regular class, but with some additional features. It has all the functionality of regular classes, plus pattern matching, automatic toString method generation, and other conveniences.
How would you implement exception handling in Scala?
Exception handling in Scala is done using a try-catch-finally block, similar to Java. The 'try' block contains the code that might throw an exception, the 'catch' block catches the exception and handles it, and the 'finally' block contains code that is always executed, regardless of whether an exception was thrown.
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What you’re looking for early on

Does the candidate have a deep understanding of Scala and its ecosystem?
Has the candidate demonstrated the ability to solve complex problems using Scala?
What is the candidate's experience with functional programming?
Does the candidate have experience with Scala's concurrency models?

Next 20 minutes

Specific Scala 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.

What is the difference between a 'null', 'Nil', 'None', and 'Nothing' in Scala?
'null' is a reference that isn't pointing to any object. 'Nil' represents an empty List of anything of zero length. 'None' is the value of an Option with no value. 'Nothing' is a subtype of all types, also used for exceptions.
What is a Trait in Scala?
A Trait in Scala is a collection of abstract and non-abstract methods. You can create a trait that has all abstract methods or some abstract and some non-abstract methods. A trait can also have fields and can be inherited by classes and other traits.
How would you implement concurrency in Scala?
Scala provides a powerful library, called Akka, to handle concurrency. Akka uses the Actor Model to handle concurrency and eliminate the complexities of direct thread manipulation.
What is the difference between a 'Seq', 'List', and 'Array' in Scala?
'Seq' is a trait which represents indexed sequences that are guaranteed immutable. 'List' is a class for immutable linked lists. 'Array' is a class to represent arrays. It can hold elements of any type.
What are Higher-Order Functions in Scala?
Higher-Order Functions are functions that take other functions as parameters and/or return functions as their result. They are a key part of the functional programming paradigm and are used extensively in Scala.
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The ideal back-end app developer

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

At this point, a skilled Scala engineer should demonstrate strong problem-solving abilities, proficiency in Scala 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 Scala.

What does the following Scala code do?
val list = List(1, 2, 3, 4, 5)
The code creates a List of integers from 1 to 5 and then reverses the order of the elements in the list.
What will be the output of the following Scala code?
val list = List(1, 2, 3, 4, 5)
val result = list.map(_ * 2)
The code multiplies each element in the list by 2 and prints the resulting list. The output will be List(2, 4, 6, 8, 10).
What does the following Scala code do?
val array = Array(1, 2, 3, 4, 5)
val result = array.filter(_ % 2 == 0)
println(result.mkString(", "))
The code filters out the odd elements from the array and prints the even numbers. The output will be '2, 4'.
What does the following Scala code do?
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

val future = Future {
  "Hello, World!"

future.onComplete {
  case Success(value) => println(value)
  case Failure(exception) => println(exception)
The code creates a Future that sleeps for 5 seconds and then returns the string 'Hello, World!'. When the Future completes, it either prints the returned string in case of success or the exception in case of failure.

Wrap-up questions

Final candidate for Scala 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 Scala application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

How would you implement pattern matching in Scala?
Pattern matching in Scala is done using the 'match' keyword. It's a powerful feature that allows you to match on any type of data, not just integers or strings.
What is the difference between 'map' and 'flatMap' in Scala?
'map' applies a function to each element of a collection and returns a new collection containing the results. 'flatMap' does the same but also flattens the result into the original format.
What is a Monad in Scala?
A Monad is a type of functional design pattern. They are used to encapsulate a value and simplify handling of unusual cases, such as null values, exceptions, or conditional logic.

Scala application related

Product Perfect's Scala development capabilities

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