10 Ruby Developer & Programmer interview questions and answers

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What are some advantages of using Ruby?

You want a programmer who can really play to the strengths of the Ruby programming language. Here are some of the key advantages of this language:

  • Pure Object-Oriented Language: Everything in Ruby is an object—even methods, classes, and booleans. This greatly simplifies things from the coder’s perspective and opens up a range of possibilities.
  • Open-Source: Ruby is 100% free and open-source, with a large and enthusiastic community that can be tapped into as a resource.
  • Metaprogramming: Ruby is widely considered to be one of the best programming languages out there for metaprogramming, or the ability to write code that can act on other code instead of data.
  • Clean and Simple Syntax: The syntax is simple and concise, which allows developers to solve complex programs with fewer lines of code. It also helps that the code is human readable, and easy to follow.

How would you freeze an object in Ruby? Can you provide a simple example?

Sometimes it can be useful to prevent an object from being changed. This can be accomplished using the freeze method (Object.freeze) as in the sample code below.

if( water.frozen? )
  puts "Water object is a frozen object"
  puts "Water object is a normal object"

Ruby provides four types of variables. List them and provide a brief explanation for each.

The four types of variables in Ruby are as follows:

  • Global variables begin with $ and are accessible from anywhere within the Ruby program regardless of where they are declared—it stands to reason that they must be handled with care.
  • Local variables begin with a lowercase letter or an underscore. The scope of a local variable is confined to the code construct within which it is declared.
  • Class variables begin with @@ and are shared by all instances of the class that it is defined in.
  • Instance variables begin with @ and are similar to class variables except that they are local to a single instance of a class in which they are instantiated.

Name the three levels of access control for Ruby methods.

In Ruby, methods may either be public, protected, or private. Public methods can be called by anyone. Protected methods are only accessible within their defining class and its subclasses. Private methods can only be accessed and viewed within their defining class.

Can you explain the role of thread pooling in relation to the thread lifecycle in Ruby?

In Ruby, the lifecycle of a single thread starts automatically as soon as CPU resources are available. The thread runs the code in the block where it was instantiated and obtains the value of the last expression in that block and returns it upon completion. Threads use up resources, but running multiple threads at a time can improve an app’s performance. Thread pooling is a technique wherein multiple pre-instantiated reusable threads are left on standby, ready to perform work when needed. Thread pooling is best used when there are a large number of short tasks that must be performed. This avoids the overhead of having to create a new thread every time a small task is about to be performed.

Can you explain how Ruby looks up a method to invoke?

Since Ruby is a pure object-oriented language, it’s important to make sure your developer thoroughly understands how objects work. The first place that Ruby looks for a method is in the object’s metaclass or eigenclass—the class that contains methods directly defined on the object. If the method cannot be found in an object’s metaclass, Ruby will then search for the method in the ancestors of an object’s class. The list of ancestors for any class starts with the class of the object itself, and climbs parent classes until it reaches the Object, Kernel, and BasicObject classes at the top of the Ruby class hierarchy. If Ruby cannot find the method, it will internally send another method aptly called “method_missing?” to the object class. Ruby will repeat another search for this method, and will at least find it in the object class, provided the programmer did not see fit to define the “method_missing?” class earlier in the ancestry of the object.

Find and fix the bug within the code below.

class Home
  attr_reader :address

  def initialize(a)
    address = a

  def call
    # perform a process that requires @address


  def address=(a)
    @address = clean(a)

  def clean(a)
    # return sanitized address

Normally if Ruby encounters an identifier, and the identifier does not reference a defined local variable, Ruby will try to call a method with the given name. However, when Ruby encounters address = a within the initialize method, it treats address = a as a local variable initialization and fails to invoke the setter. This occurs when Ruby encounters an identifier beginning with a lowercase character or underscore on the left-hand side of an assignment operator. The solution is to clarify that we want to call the writer method address = by prepending address with the self keyword. The initialize method has been reproduced below:

def initialize(a)
  self.address = a

Alternatively, you could also fix the bug by directly assigning the value to the instance variable within the initialize method like so:

def initialize(a)
  @address = clean(a)

Explain the role of modules and mixins in Ruby.

Modules are Ruby’s way of grouping methods, classes, and constants together to provide a namespace for preventing name clashes. The second purpose of modules is to use them as mixins. Technically, Ruby only supports single inheritance, but by using modules as mixins, it is possible to share code among different classes—a key advantage of multiple inheritance—without having to give up the simplicity of the single inheritance paradigm.

What are blocks and procs?

A block is basically Ruby’s version of a closure—a block of code that can be wrapped up into a proc (a type of function) that can then be stored in a variable or passed to a method and run when desired. Blocks can syntactically be written as blocks of code between { } or the do and end keywords. The standard way to create a proc is depicted in the code block below.

> my_proc = Proc.new { |arg1| print "#{arg1}! " }

Predict the output of the code below. Explain your answer.

-> (s) {p s} [“I’m a Proc”]

This question highlights the syntactical elegance of Ruby. A seasoned coder can perform a lot with a single line of Ruby code. The -> operator, or “stabby proc” as it is often called, is a way to create a proc that is also a lambda, or nameless function. This proc takes the parameter s and executes the block {p s}, which is shorthand for puts(s.inspect) before passing the string “I’m a Proc” using the square bracket syntax in place of the typical “call” method. The result is an elegant single line of code that prints the string “I’m a Proc” to the console.

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  • $50 hourly
    Ali A.
    Ruby Developer & Programmer
    • 5.0
    • (9 jobs)
    Lahore, PB
    vsuc_fltilesrefresh_TrophyIcon Ruby
    Web Services Development
    Database Design
    Ruby on Rails
    Amazon Web Services
    Web Development
    I've studied computer science. I have an experience of Web Development with the flavor of HTML, CSS, Bootstrap, JavaScript and other web development tools. I really enjoy this fact that thousands of users use applications that are developed by me. The ultimate dream is that one-day thousands will grow into millions or billions. I HAVE A DREAM! Overall if summarized my experience that would be exploring, organizing information, problem-solving and implementation. Languages are essential for expressing your programming skills overall. From EXPLORING attribute I have worked around lots of different languages. 1) Ruby 2) AngularJS 3) Javascript 4) Python ( a new sensation I always wanted to explore Erlang but then I found this beauty. Python leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant systems, while also being successfully used in web development and the embedded software domain.) In assistance to above languages below frameworks come into play, 1) Ruby on Rails 2) Laravel 3) Django Databases are the main central storage of any web application. I got experience in both SQL and NoSQL 1) Postgres 2) MongoDB 3) SQLite 4) Mysql The game never ended on the server side for me. Frontend/public facing part of the web application has been also highly evolved. Everyone wants to use Single Page Applications - The SPAs. I got experience in the following 1) Angular JS 2) React JS Testing and Test Driven Development(TDD) is also an essential thing for any solid applications. I can write automated tests in following 1) Rspec 2) Capybara 3) Mocha Deployment is essential to distribute your application out in the wild. I got experience in the following tools and technologies 1) AWS 2) Google Cloud Platforms 3) Capistrano 4) Mina 5) Nginx 6) Passenger Phusion 7) Puma 7) Unicorn
  • $90 hourly
    Stefano M.
    Ruby Developer & Programmer
    • 5.0
    • (2 jobs)
    Verona, VR
    vsuc_fltilesrefresh_TrophyIcon Ruby
    Ruby on Rails
    React Native
    Technical Project Management
    Nice to meet you! I am a CTO as a Service and entrepreneur from Italy. I started my development career in 2006 and since then I've worked with many interesting technologies, such Node, Ruby, Python and Go. As a CTO as a service, I can help your Company in a wide range of manners: - Early project stage: Helping the project owner with a strategy Defining the product roadmap (short and long term) Team hiring and training Data analysis Database design Defining application architecture Designing infrastructure architecture Choosing the right programming language and technical stack Building a PoC project Project setup and startup - During development: Team management (or your offshore team) Tasks estimation Tasks prioritization Applying agile practices Code quality review Quality assurance and testing processes Choosing a scaling strategy Choosing when and how to refactor the code Minimizing the technical debt - Project release: Assuring the quality of the final product Writing technical documentation Short and long term maintenance strategy Planning the quality assurance and testing processes Choosing a scaling strategy Defining the optimization strategy Choosing when and how to refactor the code During last 15+ years, I built every kind of web application, from monoliths to micro services to IoT related boards to every kind of client's ideas. I have dealt with: - platforms that optimize working flows - ecommerce (Spree) - quoting applications - employees evaluation and training - IoT dashboards - booking engines - mobile applications - business intelligence dashboards - ticketing systems - digital platforms for link building and digital pr - elearning tools - digital payments Currently, I'm helping clients all over the world to startup their challenging projects. Why trusting me? Because I'm a developer first, a highly skilled backend CTO and an entrepreneur. Hire me for your next big project. Stefano Mancini
  • $65 hourly
    Randall B.
    Ruby Developer & Programmer
    • 5.0
    • (34 jobs)
    Phoenix, AZ
    vsuc_fltilesrefresh_TrophyIcon Ruby
    AWS Development
    Query Optimization
    Data Scraping
    Web Development
    Ruby on Rails
    5 years of Ruby on Rails fullstack (front-end, back-end and deployment) experience. 5 years deploying on the cloud (AWS, Azure, Digital Ocean, Heroku) 2 years Rust experience. Certified Kubernetes Administrator (CKA) Hashicorp Certified - Terraform Associate 003 I'm 100% committed to achieve success in your web applications with the results to prove it. Previous project work includes: ● Setting up 1-to-1 voice conferences using Twilio API ● Custom 2 factor authentication implementation ● Uploading and storing data on S3 and B2 buckets ● Automated web crawling to monitor new legislation ● Custom cron jobs on Linux servers for backup and maintenance tasks ● Solving "impossible" problems with custom Ruby gem and Rails patches ● Mass marketing sms campaigns using Twilio API ● Complex custom subscription implementation with Stripe API Technology I work with: ● Ruby on Rails (RoR). Rails 4, 5, 6, 7. ● Hotwire/Turbo ● RSpec/Capybara/Selenium for unit testing and feature testing ● PostgresDB, Mysql ● Heroku, Digital Ocean, AWS EC2 servers ● Heroku staging apps for continuous integration (CI/CD) ● Twilio API, Stripe API ● Google/Facebook/LinkedIn OAuth ● Capistrano, Docker+Kubernetes for deployment ● Wordpress, Shopify ● HTM5L/CSS3 ● JavaScript/AJAX/JQuery/JSON ● ReactJs/Nodejs/Typescript ● Web Scraping ● Linux BASH scripting ● Git, GitHub, Bitbucket, ● Webhooks ● Performance enhancement via algorithm and query optimization I understand the importance of test driven development to ensure a product that is understandable and maintainable for future developers to work on. More time put in up front means far less costs down the road. Fluent in English. Born and raised in the USA.
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