Introduction to Ruby

Who am I?

Carolina Pascale Campos

Intern at Codeminer42

Student at UFSCar

https://github.com/CarolPC

Installation

https://rvm.io

Conventions

• File/Directory lower case
• Identation: two spaces
• _ for variable name
• One quote for Strings
• @variable ||= "default value"
• && (and)

Features

• Case sensitive

Comments

• Anything followed by a #
• For large blocks of code, anything between =begin and =end

Example 1

# p001rubyhelloworld.rb

=begin
  Printing a hello world in ruby.
        Testing a block comment.
=end

hello_world = 'Hello World, Ruby!'

puts hello_world

Nil and false

• Everything is true, except for nil and false.
• Zero, null character, [] are true.

Everything is an object

• String
• Numbers

Example 2

# p002rubyobject.rb
#everything is an object in ruby

puts 'I am Batman'.class
puts 29.to_s
puts 'Why so serious ' + 3.to_s

Strings

• Objects
• to_s
• s * 9
• <<
• Interpolation/Placeholder

Example 3

# p003rubystrings.rb

# strings are objects
puts 'But you dont\'t know fear half as well as it knows you.'.class

# how to convert to a string and print many times
number = 3
puts number.to_s * 4

# append to a string
batman = 'And Batman?'
batman << 'I\'m not sure what scares him.
Maybe hes driven by his fears..'
puts batman

# String interpolation
placeholder = 'use string interpolation'
puts "I can #{placeholder} when using double quoted strings"

Numbers

Example 4

# p004rubynumbers.rb

=begin
	Ruby Numbers
	Usual operators
	+ addition  
	- subtraction  
	* multiplication  
	/ division  
=end

puts 1 + 2
puts 2 * 3

# Integer division
# When you do arithmetic with integers, you'll get integer answers  

puts 3 / 2
puts 10 - 11
puts 1.5 / 2.6

Methods

• Returns the value of the last line
• If they act as queries, are often named with ?
• To modify the receiver use !

Example 5

# p005mymethods.rb

def batman
  'Batman'
end

#use the method
puts batman

quote = 'Why so serious?'
# Method that does not modify the variable
def updateQuoteFalse quote
  quote = quote.reverse
end

# Method that does modify the variable
def updateQuoteTrue quote
  quote = quote.reverse!
end

updateQuoteFalse(quote)
puts quote

updateQuoteTrue(quote)
puts quote

Symbols

• Objects
• Immutable, reusable constants.
• Meaningful values

Example 6

# p006rubysymbols.rb

puts :danger.class

status = :danger

puts status == :danger
puts status == 'danger'
puts status == :safe

Arrays

• Objects
• reverse
• <<
• push
• include?

Example 7

# p007rubyarray.rb

a = ['Harley Quinn', 30, true]
a.reverse!
a << 'Joker'

puts "Playing with #{a}"
puts a.include?('Joker')

Unless and If

• unless with else is confusing
• inline conditionals
• conditional assignment

Example 8

#p008rubyconditional.rb

character = 'Batman'

# Bad code
if character != nil
  puts 'Bad'
end

# Good code
if character
  puts 'Good'
end

# Conditional assignment
character ||= 'Joker'
puts character

villain ||= 'Joker'
puts villain

villain = 'Harley Quinn'

# Inline conditionals and unless
puts 'There is no villain' unless villain
puts villain if villain

Hash

• Primary dictionary with key/value pairs
• Denoted with curly braces

Example 9

#p009rubyhash.rb

# Bad code. Long parameter list
def villain(name, firstAppearance = nil, age = nil, quote = nil)

def hero(name, options{}){
  character = hero.new
  character.firstAppearance = options[:firstAppearance]
  character.age = options[:age]
  character.quote = options[:quote]
}

hero('Batman',
  :firstAppearance => 1938,
  :age => 36
  :quote => 'I am Batman'
) #keys show meaning

Class

• attr_accessor
• self
• re-open

Example 10

#p010rubyclass.rb

class Character
  attr_accessor :name, :firstAppearance
  def initialize(name, firstAppearance)
    @name = name
    @firstAppearance = firstAppearance
  end
end

batman = Character.new('Batman', 1938)

# Re-opening a class
class Character
  def to_s
    "I am #{name} and my first appearance was in #{firstAppearance}"
  end
end

puts batman.to_s

Case

• ranges
• when/then

Example 11

#p011rubycase.rb

result = 29

score = case result
when 0..9
nil
when 10..29
"great"
else
"amazing"
end

score_type = case result
  when 29 then :great
end

puts score
puts score_type

Exception

Example 12

#p012rubyexception.rb

# exception handling:
begin
  # code here that might raise an exception
  raise NoMemoryError, 'You ran out of memory.'
  rescue NoMemoryError => exception_variable
    puts 'NoMemoryError was raised', exception_variable

  rescue RuntimeError => other_exception_variable
    puts 'RuntimeError was raised now'

  else
    puts 'This runs if no exceptions were thrown at all'

  ensure
    puts 'This code always runs no matter what'
end

Useful links to learn more!

• https://www.ruby-lang.org/en/documentation/
• http://rubylearning.com/satishtalim/tutorial.html
• https://www.codeschool.com
• https://learnxinyminutes.com/docs/ruby/
• http://www.akitaonrails.com

Thanks for your attention!

Any questions?