Hiring guide for Elixir Engineers

Elixir Developer Hiring Guide

Elixir is a dynamic, functional programming language designed for building scalable and maintainable applications. It was created by José Valim in 2011 to enable higher extensibility and productivity in the Erlang VM while maintaining compatibility with Erlang's ecosystem. Elixir leverages the Erlang BEAM (Bogdan's Erlang Abstract Machine) to build distributed, fault-tolerant applications with real-time guarantees and hot code upgrades. The language provides metaprogramming capabilities through macros, polymorphism via protocols, and support for concurrency. Elixir has been adopted by companies like Pinterest and Moz for its robustness, performance, and scalability.

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

First 20 minutes

General Elixir app knowledge and experience

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

How would you define Elixir?
Elixir is a dynamic, functional language designed for building scalable and maintainable applications. It leverages the Erlang VM, known for running low-latency, distributed, and fault-tolerant systems.
What are the key features of Elixir?
Some key features of Elixir include its scalability, fault tolerance, functional programming, extensibility, and compatibility with the Erlang ecosystem.
How would you install Elixir in your local machine?
You can install Elixir using various package managers depending on your operating system. For example, on macOS, you can use Homebrew and run 'brew install elixir'.
What is Mix in Elixir?
Mix is a build tool that provides tasks for creating, compiling, and testing Elixir projects, managing its dependencies, and more.
How would you define a module in Elixir?
In Elixir, you define a module using the 'defmodule' keyword followed by the module name and do/end block. Inside the block, you can define functions using 'def' keyword.
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What you’re looking for early on

Does the candidate have a solid understanding of Elixir's syntax and semantics?
Can the candidate demonstrate experience with OTP (Open Telecom Platform)?
Is the candidate able to solve problems effectively and efficiently using Elixir?
Does the candidate have experience with Elixir's testing tools like ExUnit?

Next 20 minutes

Specific Elixir 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 are the data types supported by Elixir?
Elixir supports several data types such as integers, floats, booleans, atoms, strings, lists, tuples, maps, and binary.
How would you handle errors in Elixir?
Elixir uses a mechanism called 'exceptions' to handle errors. You can raise an exception using 'raise' function and handle it using 'try/rescue' construct.
Describe the difference between '==' and '===' in Elixir.
'==' operator compares the values and returns true if they are equal. '===' operator, on the other hand, is more strict and also considers the data type of the values.
What is pattern matching in Elixir?
Pattern matching is a powerful feature in Elixir that allows you to match simple as well as complex data structures, destructure data, and control program flow.
How would you implement concurrency in Elixir?
Elixir provides first-class support for concurrency. You can create lightweight processes using 'spawn' function, send messages to them using 'send' function, and receive messages using 'receive' construct.
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The ideal back-end app developer

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

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

What does the following Elixir code do?
IO.puts "Hello, World!"
This code prints the string 'Hello, World!' to the console.
What will be the output of the following Elixir code?
IO.inspect(Enum.map([1, 2, 3, 4], fn x -> x * 2 end))
This code will output a list of numbers [2, 4, 6, 8]. It uses the Enum.map function to iterate over the list [1, 2, 3, 4] and multiplies each element by 2.
What does the following Elixir code do?
Enum.reduce([1, 2, 3], 0, fn(x, acc) -> x + acc end)
This code sums up the elements in the list [1, 2, 3]. It uses the Enum.reduce function, which takes an enumerable, an accumulator (initial value), and a function. The function is applied to each element in the enumerable, and the result is accumulated.
What does the following Elixir code do?
Task.async(fn -> 1 + 2 end) |> Task.await
This code executes the function (1 + 2) asynchronously in a separate process and waits for the result. It uses the Task.async function to start an asynchronous task and Task.await to get the result of the task.

Wrap-up questions

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

What is OTP in the context of Elixir?
OTP (Open Telecom Platform) is a set of libraries and design principles in Erlang that Elixir leverages to build robust, fault-tolerant, distributed applications.
Describe the difference between 'list' and 'tuple' in Elixir.
Lists are stored in memory as linked lists, making it efficient to insert elements at the head. Tuples, on the other hand, are stored contiguously in memory, making it efficient to access an element by index.
How would you create a GenServer in Elixir?
You can create a GenServer by defining a module and using 'GenServer' behaviour. The module needs to implement two callback functions: 'init/1' and 'handle_call/3'.

Elixir application related

Product Perfect's Elixir development capabilities

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