Hiring guide for Ruby Engineers

Ruby Developer Hiring Guide

Ruby is a high-level, interpreted programming language developed in the mid-1990s by Yukihiro "Matz" Matsumoto in Japan. It is a dynamic, open-source language with a focus on simplicity and productivity. Ruby has an elegant syntax that is natural to read and easy to write, making it ideal for scripting and rapid application development. It supports multiple programming paradigms, including procedural, object-oriented, and functional programming. Ruby is also known for its use in the Ruby on Rails web framework, which is implemented in Ruby.

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

First 20 minutes

General Ruby app knowledge and experience

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

How would you define Ruby on Rails?
Ruby on Rails, often just Rails, is an open-source web application framework written in Ruby. It follows the Model-View-Controller architectural pattern. It emphasizes the use of convention over configuration and the Don't Repeat Yourself principle.
What are the different types of variables in Ruby?
In Ruby, there are four types of variables: Local variables, Instance variables, Class variables, and Global variables.
Describe the difference between a class and a module in Ruby.
The main difference between classes and modules in Ruby is that classes can be instantiated as objects while modules cannot. Modules are used to group similar methods, classes or constants.
How would you explain the use of yield in Ruby?
Yield in Ruby is a keyword that allows you to pause and resume code execution. It is used in conjunction with a block of code. When the yield keyword is encountered, Ruby stops executing the method and starts executing the block. After the block finishes, control returns to the method body, right after where the yield statement was.
What are Ruby Gems and how would you use them?
Ruby Gems are the main method for packaging Ruby programs and libraries in a format that can be easily managed and deployed. They are used by requiring them at the top of your Ruby files and then calling the methods that they provide.
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What you’re looking for early on

Does the candidate have a deep understanding of Ruby and its associated frameworks?
Has the candidate demonstrated problem-solving skills?
Does the candidate have experience with test-driven development?
Can the candidate work well in a team?

Next 20 minutes

Specific Ruby 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 instance and class methods in Ruby.
Instance methods are methods that are available on instances of a class. Class methods, on the other hand, are methods that are available on the class itself, not instances of the class.
How would you handle exceptions in Ruby?
Exceptions in Ruby are handled using the begin, rescue, and end keywords. The begin block contains the code that might raise an exception, and the rescue block contains the code that will be executed if an exception does occur.
What are some ways to iterate over an array in Ruby?
There are several ways to iterate over an array in Ruby. Some of the most common ones are using the each, map, and select methods.
Describe the difference between a symbol and a string in Ruby.
Symbols are immutable and reusable, meaning the same symbol value corresponds to the same memory object throughout a Ruby program. Strings, on the other hand, are mutable and more flexible, but they can take up more memory as each instance is a new object.
How would you explain the difference between a Proc and a Lambda in Ruby?
Both Procs and Lambdas are objects that encapsulate a block of code in Ruby. The key differences between them are how they handle arguments and control flow. Lambdas check the number of arguments, while Procs do not, and Lambdas return control to the calling method, while Procs return from the method that they are executed in.
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The ideal back-end app developer

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

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

What does the following Ruby code do?
def greet(name)
  "Hello, #{name}!"
This code defines a method called 'greet' that takes one argument 'name'. It then interpolates the 'name' into a string and returns a greeting. When called with the argument 'Ruby', it will return 'Hello, Ruby!'.
What will be the output of the following Ruby code?
5.times do |i|
  puts i
This code will print the numbers 0 through 4, each on a new line. The 'times' method is called on the integer 5, and for each iteration, it yields to the block, passing in the current iteration number (starting from 0).
What does the following Ruby code do?
[1, 2, 3, 4, 5].map { |n| n * 2 }
This code takes an array of numbers from 1 to 5, and uses the 'map' method to create a new array where each element is the result of multiplying the corresponding element in the original array by 2. The result will be [2, 4, 6, 8, 10].
What does the following Ruby code do?
Thread.new do
  puts 'Hello from a thread'
This code creates a new thread that executes the code within the block, which is to print 'Hello from a thread'. The 'join' method is called on the thread to ensure that the main program waits for the thread to finish execution before it exits.

Wrap-up questions

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

What are the main features of Ruby on Rails?
Some of the main features of Ruby on Rails include MVC architecture, Database abstraction, Convention over Configuration, and Don't Repeat Yourself principles.
How would you implement caching in Rails?
Rails provides several caching techniques: page, action, fragment, low-level caching and SQL caching. The choice of caching technique depends on the specific use case.
Describe the difference between a has_one and belongs_to association in Rails.
In Rails, has_one and belongs_to are both used to set up one-to-one connections between models. The main difference is in where the foreign key is located. In a has_one association, the foreign key is on the associated model. In a belongs_to association, the foreign key is on the model declaring the association.

Ruby application related

Product Perfect's Ruby development capabilities

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