ruby_interview_questions.md

Authored on Sep 2015

To make sure we hire a top class rubyist, and -- to select the cream of the crop -- these set of questions are specifically written for such interview, kind of ruby benchmark. Hiring a candidate who has the correct grasp on the concepts in 30 minutes of the interview duration is a challenge altogether. I hope this help all folks.

High expectations

Our expectations are generally high while interviewing and candidates will give you a variety of responses based on their experience and knowledge. So it's up to the interviewer to decide the correctness of the answers.

There can be many possible approaches to these questions -- some aren't mentioned here. This list is not complete, by any means and I welcome your suggestions to this.

How does a symbol differ from a string?

Short answer: symbols are immutable and reusable, retaining the same object_id.

Be prepared to discuss the benefits of using symbols vs. strings, the effect on memory usage, and in which situations you would use one over the other.

Explain how (almost) everything is an object in Ruby.

Here’s your chance to show off your theoretical knowledge and demonstrate that you can have an in depth conversation on class hierarchies, inheritance, methods, encapsulation, polymorphism, and more.

What is a class?

Parrot answer: classes are a blue-print for constructing computer models for real or virtual objects... boring.

In reality: classes hold data, have methods that interact with that data, and are used to instantiate objects.

Like this.

class WhatAreClasses
  def initialize
    @data = "I'm instance data of this object. Hello."
  end

  def method
    puts @data.gsub("instance", "altered")
  end
end

object = WhatAreClasses.new
object.method
 #=> I'm altered data of this object. Hello.

What is an object?

Parrot answer : An instance of a class.

It's also the root class in ruby (Object). Classes themselves descend from the Object root class.

Can you tell me the difference between classes and modules?

Modules serve as a mechanism for namespaces.

module ANamespace
  class AClass
    def initialize
      puts "Another object, coming right up!"
    end
  end
end

ANamespace::AClass.new
 #=> Another object, coming right up!

Also, modules provide as a mechanism for multiple inheritance via mix-ins and cannot be instantiated like classes can.

Tell me the access specifiers in ruby? What do they imply about the method?

All methods, no matter the access control, can be accessed within the class. But what about outside callers?

Public methods enforce no access control -- they can be called in any scope.

Protected methods are only accessible to other objects of the same class.

Private methods are only accessible within the context of the current object.

Can you tell me the approaches to invoke a method in ruby?

object = Object.new
puts object.object_id
 #=> 282660

puts object.send(:object_id)
 #=> 282660

puts object.method(:object_id).call
 #=> 282660

Explain this syntax: a ||= b

a = 1
b = 2
a ||= b #=> a = 1

a = nil
b = 2
a ||= b #=> a = 2

a = false
b = 2
a ||= b #=> a = 2

What is a Proc?

Essentially, Procs are anonymous methods (or nameless functions) containing code. They can be placed inside a variable and passed around like any other object or scalar value. They are created by Proc.new, lambda, and blocks (invoked by the yield keyword).

# wants a proc, a lambda, AND a block
def three_approaches(proc, lambda, &block)
  proc.call
  lambda.call
  yield # like block.call
  puts "#{proc.inspect} #{lambda.inspect} #{block.inspect}"
end

anonymous = Proc.new { puts "I'm a Proc for sure." }
nameless  = lambda { puts "But what about me?" }

three_approaches(anonymous, nameless) do
  puts "I'm a block, but could it be???"
end
 #=> I'm a Proc for sure.
 #=> But what about me?
 #=> I'm a block, but could it be???
 #=> #<Proc:0x00089d64> #<Proc:0x00089c74> #<Proc:0x00089b34>

What is unit testing ?

Unit testing, simply put, is testing methods -- the smallest unit in object-oriented programming. The primary way to achieve this is to assert that the actual result of the method matches an expected result.

require "test/unit"

class Greet
  def say
    "Hello ruby"
  end
end

class GreetTest < Test::Unit::TestCase
  def test_say
    greet = Greet.new
    assert_equal("Hello!", greet.say)
  end
end
 #=> Started
 #=> F
 #=> Finished in 0.663831 seconds.
 #=> 
 #=>   1) Failure:
 #=> test_say:11
 #=> <"Hello!"> expected but was
 #=> <"Hello ruby">.
 #=> 
 #=> 1 tests, 1 assertions, 1 failures, 0 errors

What is the difference between calling super and calling super()?

A call to super invokes the parent method with the same arguments that were passed to the child method. An error will therefore occur if the arguments passed to the child method don’t match what the parent is expecting.

A call to super() invokes the parent method without any arguments, as presumably expected. As always, being explicit in your code is a good thing.

What is the use of load and require in ruby?

Require() loads and processes the Ruby code from a separate file, including whatever classes, modules, methods, and constants are in that file into the current scope.

Load() performs the inclusion operation once, it reprocesses the code every time load is called.

Your Own Questions?

Please share your ideas / feedback with us!