Top 10 Ruby Developer Interview Questions & Answers in 2024

1. How does Ruby's garbage collection work, and what strategies can be employed to optimize memory usage in a Ruby application?

Ruby employs a garbage collector to automatically manage memory. The garbage collector identifies and collects objects that are no longer reachable. Strategies to optimize memory usage include minimizing unnecessary object creation, using efficient data structures, and utilizing tools like the ObjectSpace module to analyze memory usage. Regularly profiling the application with tools like ruby-prof can help identify memory bottlenecks.

2. Explain the concept of metaprogramming in Ruby and provide an example of how it can be used to dynamically define methods.

Metaprogramming in Ruby involves writing code that manipulates the language's constructs during runtime. One example is dynamically defining methods using the define_method or method_missing techniques. For instance, defining getters and setters dynamically:

class Example
  attr_accessor :name

  def self.create_accessor(name)
    define_method(name) { instance_variable_get("@#{name}") }
    define_method("#{name}=") { |value| instance_variable_set("@#{name}", value) }
  end
end

3. What are Ruby gems, and how do you create, install, and manage them in a project?

Ruby gems are packages or libraries that provide reusable pieces of code. To create a gem, use the bundle gem command. To install a gem, use gem install gem_name. Bundler is a tool for managing gem dependencies in a project. Add gem dependencies to the Gemfile, then run bundle install. The Gemfile.lock file ensures consistent gem versions across different environments.

4. Discuss the differences between symbols and strings in Ruby, and when would you choose one over the other?

Symbols and strings are both used to represent names, but symbols are immutable and unique, whereas strings are mutable. Symbols are typically used for identifiers (like keys in hashes) due to their efficiency and immutability, while strings are more suitable for cases where mutability is required, such as modifying the content dynamically.

5. Explain the purpose of Rack in the context of Ruby web applications, and how does it simplify the development of web frameworks?

Rack is a web server interface for Ruby web applications. It provides a standardized way for web frameworks (e.g., Sinatra, Ruby on Rails) to communicate with web servers. Rack middleware allows developers to add functionality to their web applications, such as authentication or caching, in a modular and composable manner. Rack simplifies the development of web frameworks by providing a common interface for handling HTTP requests and responses.

6. What is the difference between Procs and Lambdas in Ruby, and when would you use one over the other?

Both Procs and Lambdas are objects representing blocks of code. The key difference lies in how they handle return statements and argument checking. Lambdas enforce the number of arguments passed, whereas Procs do not. Use Lambdas when strict argument checking is necessary, and Procs when flexibility in the number of arguments is acceptable.

7. How can you optimize the performance of a Ruby on Rails application, and what tools or techniques would you use for profiling?

Optimizing a Ruby on Rails application involves strategies like eager loading, caching, and database indexing. Use tools like Bullet for N+1 query detection and rack-mini-profiler for profiling. The benchmark module can be employed for measuring execution times. Analyzing database queries with tools like rails db:explain helps identify and optimize slow queries.

8. Explain the concept of ActiveSupport in Ruby on Rails, and provide examples of its usage.

ActiveSupport is a Ruby on Rails component that provides utility classes and extension methods to Ruby's standard library. It adds functionality like date and time handling, string manipulation, and more. For example, ActiveSupport's 3.days.ago simplifies date calculations, and String#pluralize makes it easy to pluralize words based on count, enhancing code readability and conciseness.

9. Describe the differences between a symbol, a keyword, and a variable in the context of Ruby, and when would you choose one over the other?

Symbols are immutable identifiers, keywords are reserved words in the language, and variables hold references to objects. Symbols are typically used for names, keywords for language constructs, and variables for storing data. Use symbols for hash keys, keywords for defining method arguments or options, and variables for general data storage.

10. How does ActiveRecord handle database migrations, and what are some best practices for managing database schema changes in a Ruby on Rails project?

ActiveRecord provides a migration framework to manage database schema changes. Migrations are Ruby files defining changes to the database schema. Use commands like rails db:migrate to apply migrations. Best practices include versioning schema changes with timestamps, writing reversible migrations, and using tools like annotate_models to document schema information directly in the model files. Regularly back up databases before applying migrations to prevent data loss.