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Ruby On Rails Interview Questions and Answers

Ques 1. What are Class Variables? How to define them?

Class variables are created using the @@ prefix to denote the variable as class level. 

It works just like any other variable, however in the case of inheritance it works more like a static variable that is accessed across all variable instances.

Another example can be found here:

class DemoClass 
 @@my_var = nil
  def initialize
    @@my_var = "hello world"
  def my_var
    puts @@my_var
class Demo2Class < DemoClass
  def initialize
    @@my_var = "goodbye world"
demo1 =
demo2 =
The output would be as shown below:
hello world
goodbye world
goodbye world

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Ques 2. How to define Instance variables?

Instance variables are defined using single @ symbol.

@foo = "Hello"

Within a class they can be declared as below:

class Animal
 attr_accessor :name, :age

Next you can query an object instance to find which instance variables it has.

anim =
=> [ ]"John"
anim.age = 3
 => [:@age, :@name] 

In the above case we did not put the @ symbol before the instance variables but it is implied. 

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Ques 3. How can you dynamically define a method body in Ruby on Rails?

An instance method can be defined dynamically with

Module#define_method(name, body),

where name is the methodís name given as a Symbol, and body is its body given as a Proc, Method, UnboundMethod, or block literal. This allows methods to be defined at runtime, in contrast to def which requires the method name and body to appear literally in the source code.

class Conjure
  def self.conjure(name, lamb)
    define_method(name, lamb)

# Define a new instance method with a lambda as its body

Conjure.conjure(:glark, ->{ (3..5).to_a * 2 }) #=> [3, 4, 5, 3, 4, 5]  

Module#define_method is a private method so must be called from within the class the method is being defined on. Alternatively, it can be invoked inside class_eval like so:

Array.class_eval do
  define_method(:second, ->{ self.[](1) })
[3, 4, 5].second #=> 4

Kernel#define_singleton_method is called with the same arguments as Module#define_method to define a singleton method on the receiver.

File.define_singleton_method(:match) do |file, pattern|
File.match('/etc/passwd',/root/) #=> #<MatchData "root">

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Ques 4. What is Range?

Range is a great way to declare continuous variables. You should use it to declare arrays and other types of collections. 

range1 = (1..4).to_a
 => [1, 2, 3, 4] 
puts range1

You can also create strings in this format and it fills in the interim values automatically.

range2 = ('bar'..'bat').to_a
puts range2
Since the end result of using range is an array you can also iterate over it just like any other array.
range2.each do |str|
   puts "In Loop #{str}"

This produces the result as shown below:

In Loop bar
In Loop bas
In Loop bat

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Ques 5. How can you implement method overloading in Ruby on Rails?

This oneís a tricky question. If you have a background in Java then you must know that method overloading is simply multiple methods with same name but different signatures/parameters.

In the case of Ruby method overloading is not supported. 

However, it does support the overall goal of passing variable number of parameters to the same method. You would implement it like this:

class MyClass  
  def initialize(*args)  
    if args.size < 2  || args.size > 3  
      puts 'This method takes either 2 or 3 arguments'  
      if args.size == 2  
        puts 'Found two arguments'  
        puts 'Found three arguments'  

The output can be seen here:[10, 23], 4, 10)  
Found three arguments[10, 23], [14, 13]) 
Found two arguments

SO: You can get the same effect as method overloading but you just have to manage the number of variables inside your method itself.

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