29.4.2021 Ruby Quiz

Question 1

Can case statement be assigned to any variable?

Answer 1

yes. This value can be assigned to a variable preceding the case statement.

happy = case

when …

end

puts happy

Question 2

What is the difference between Date and DateTime classes?

Answer 2

The Date class has no concept of minutes, seconds or hours. This class stores everything internally in terms of days.

The DateTime class is a subclass of Date and it can store seconds in addition to dates.

Question 3

> 3.days.ago

Is this valid method in Ruby? If not,

How we can get this output?

Answer 3

These methods are not available in pure Ruby,
they are added by the ActiveSupport component of Rails.

1. day # ActiveSupport::Duration
2. days.ago # ActiveSupport::TimeWithZone

Question 4

Consider the error. How to fix it?

irb(main):001:0> Date.today
Traceback (most recent call last):
2: from /Library/Ruby/Gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `'
1: from (irb):1
NameError (uninitialized constant Date)
Did you mean? Data

Answer 4

To use the Date class you need to

> require ‘date’.

You can get the current date using Date.today.

irb>Date.today

Question 5

How to get all the month names and Week days names from Date class?

Answer 5

The Date class has some constants.

For example, there is an array with the months of the year and another with the days of the week.

require ‘date’

puts Date::MONTHNAMES #all months
puts Date::DAYNAMES #all days

Question 6

What are the ways to read a file using File class?

Answer 6

There are three different methods to read a file.

To return a single line, following syntax is used.

Syntax: f.gets
code…
To return the whole file after the current position, following syntax is used.

Syntax: f.read
code…
To return file as an array of lines, following syntax is used.

Syntax: f.readlines
[code…]

Question 7

What are the Socket library subclasses from IO?

Answer 7

TCPSocket , UDPSocket ,UNIX Socket

Question 8

What are the following open mode implies?

w+
r+
a+

Answer 8

“w+” Read-write, truncates existing file to zero length
or creates a new file for reading and writing.

“r+” Read-write, starts at beginning of file.

“a+” Read-write, each write call appends data at end of file.
Creates a new file for reading and writing if file does
not exist.

Question 9

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

Answer 9

super - sends all arguments

super() - no arguments

Question 10

Difference between prepend and extend keywords?

Answer 10

prepend keyword need object creation from class when
being called.

Extend keyword don’t need object when being called

module Commentable
def comment
puts 'I love comments!'
end
end

class Post
extend Commentable
def comment
puts'I comment!'
end
end

Post.comment # I love comments!
#if its prepend keyword you need to do

Post.new.comment

Question 11

Is this code valid?

def: increment(x) = x + 1

Answer 11

yes.

Ruby 3 new feature. Endless method

p increment(42) #=> 43

Question 12

user = { name: ‘Oliver’, age: 29, role: ‘CTO’ }

in this code how you will print name and age pair alone?

Answer 12

user.except(:role)

Ruby 3 feature : except method

earlier we need to use active support in rails to do that

Question 13

What is the use of backtrace method in Exception?

Answer 13

This method returns any backtrace associated with the exception. The backtrace is an array of strings, each containing either “filename:lineNo: in `method”‘ or “filename:lineNo.”

Question 14

What does the following code return?

browsers = {
  :favorite => :chrome,
  :favorite => :firefox,
  :worst => :internet_explorer
}
browsers[:favorite]

Answer 14

:firefox
Duplicate keys are not allowed in a hash. When Ruby detects a duplicate key, it simply deletes the first key / value pair that is a duplicate.

Question 15

Is the following hash valid?

weird_hash = {
[1, 2, 3] => Object.new(),
Hash.new => :mousie
}

Answer 15

The weird_hash is odd, but valid. Any object can be a key or value in a Ruby hash.

Symbols are typically used as hash keys because they are descriptive and efficient, but any object can be used.

Question 16

What does the following code print? Explain.

class Dog; end
p Dog.ancestors

Answer 16

[Dog, Object, Kernel, BasicObject]

The Dog class inherits from the Object class and the Object class inherits from the BasicObject class.

The Kernel module is mixed-in to the Object class. All user defined classes inherit from the Object class by default.

BasicObject is a very simplistic class and is not commonly used.

The Kernel module defines methods that are commonly used in Ruby like raise() and puts().

Question 17

What does the following code print? Explain.

module AAA
  def hi; 'AAA#hi'; end
end

class Money
  class << self
    include AAA
  end
end

p Money.hi

Answer 17

"AAA#hi"
The 'class << self' syntax is used to change the scope to Money's singleton class. The module's methods are added to the singleton class as instance methods when the module is included in the singleton class.

Money.singleton_methods # => [:hi]

Question 18

What does the following code print? Explain.

module M
  def hi
    'hey hey'
  end
end

class A
include M
end

p A.instance_methods.include? :hi

Answer 18

true

Methods defined in a module are accessible as instance methods when the module is included in a class.

Question 19

What does the following code print? Explain.

p self
p "***"
class Example
  p self
end

Answer 19

main
“***”
Example

A program starts in the top level scope. When the program encounters the class keyword, the scope changes to the class. When the context changes (the terms context and scope are synonymous), the self keyword is reassigned to a different object.

Question 20

What does the following code print? Explain.

bieber = 'person'
class Weird
  y = 'boo'
  def hi
    z = 'sleepy generation'
  end
end
fever = 'sickness'

p local_variables

Answer 20

[:bieber, :fever]

The program starts in the top level scope where the bieber local variable is defined. When the program encounters the class keyword, it exits the top level scope and does not return to the top level scope until the class definition is ended. The fever local variable is defined in the top level scope when it is reopened.