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Week-02-Intermediate-Ruby.md

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Week 2 - Intermediate Ruby and Git

Questions from homework?

My solution

puts "Tell me a word, any word: "
word = gets.strip

if word == word.reverse
  puts "It's a palendrome!"
else
  puts "Nope, not a palendrome"
end

Could also downcase to do a case insensitive match.

More Ruby

Methods

  • A chunk of code that can be run over and over

    • Parameters allow input
    • Return values allow output
    # Orignally
puts "Hello Larry!"
puts "Hello George!"

# New
def greeting(name)
    "Hello #{name}!"
end

puts greeting("Larry")
puts greeting("George")

    # Original
words = ["fred","racecar"]

words.each do |w|
    if w == w.reverse
    puts "It's a palendrome!"
    else
    puts "Nope, not a palendrome"
    end
end

# New
def is_palendrome?(word)
    word == word.reverse
end

words = ["fred","racecar"]

words.each do |w|
    if is_palendrome?(word)
    puts "It's a palendrome!"
    else
    puts "Nope, not a palendrome"
    end
end

  • last line of method is what is returned.

  • Simple methods can be called with or without parenthises

    is_palendrome?(word)
is_palendrome? word

def print_palendrome_message palendrome_status, success_message, failure_message
  if palendrome_status
    puts success_message
  else
    puts failure_message
  end
end

print_palendrome_message is_palendrome? word, "Yep", "Nope"
print_palendrome_message is_palendrome?(word), "Yep", "Nope"

  • Default arguments

      def print_palendrome_message(palendrome_status, success_message = "Yep", failure_message = "Nope")
    if palendrome_status
      puts success_message
    else
      puts failure_message
    end
  end

  result = is_palendrome? "Fred"
  print_palendrome_message result

  • Hash arguments

    def print_palendrome_message(palendrome_status, options={})
  # Implementation here
end

result = is_palendrome? "Fred"
print_palendrome_message result, success: "Yep", failure: "Nope"
# Same as print_palendrome_message(result, {success: "Yep", failure: "Nope"})

  • Detour into hashes, symbols and default values

    • Symbols - simple strings. Mainly used for hash keys

      string_hash = { "name" => "Fred", "age" => 35 }
string_hash["name"]

symbol_hash = { :name => "Fred", :age => 35 }
symbol_hash[:name]

# Ruby 1.9+ hash syntax
{name: "Fred", age: 35}

    • Comparisons

      def is_chosen?(person)
  if person[:name] == "Fred" || person[:age] > 30
    true
  else
    false
  end
end

is_chosen? {name: "Fred", age: 28 } #=> true
is_chosen? {name: "George", age: 58 } #=> true
is_chosen? {name: "Amy", age: 22 } # false

# Can rewrite method to
def is_chosen?(person)
  name == "Fred" || age > 30
end
      • Logical Operators
        • && - And - both values have to be true. If first value is false, it doesn't try the second comparison
        • || - Or - one of the values has to be true. If the first value is true, it doesn't try the rest.
        • ! - Not
      • Use parenthesis for grouping
      • Comparison cheat sheet

    • Truthy or falsey

      def truthy_or_falsey(value)
  if value
    "truthy"
  else
    "falsey"
  end
end

puts truthy_or_falsey nil
      • Truthy - "word", "", [], 0, true
      • Falsey - nil, false

    • Default hash values

      fred = {name: "Fred", age: 35, knows_html: false }
james = {name: "James", age: 24, job: "Lead developer" }

fred[:job] #=> nil

fred[:job] || "No job given" #=> "No job given"

james[:knows_html] || "No information provided"  #=> "No information provided"
james[:knows_html] || "No information provided"  #=> "No information provided"

james.fetch(:knows_html){ "No information provided" } #=> false

  • Bringing it all together

    def print_palendrome_message(palendrome_status, options={})
  success_message = options[:success] || "Yep"

  #Another version of default assignment
  failure_message = options[:failure]
  failure_message ||= "Nope"  # Sames as failure_message = failure_message || "Nope"

  # Could also use failure_message = options.fetch(:failure){ "Nope" }

  if palendrome_status
    puts success_message
  else
    puts failure_message
  end
end

result = is_palendrome? "Fred"
print_palendrome_message result, success: "Yep", failure: "Nope"

Objects and classes

  • Class

  • Object

    • Instance of a class

    • Usually created by class.new

    • Everything is an object. Objects have methods and a class

      "Hello world".class # => String
"Hello world".class.class # => Class

"Hello world".methods #=> [:<=>, :==, :===, :eql?, :hash, :casecmp, ...]

    • Constructors

      a = Array.new 5
puts a.inspect #=> [nil, nil, nil, nil, nil]

b = ["javasript", "ruby"] # This is a "literal". It also creates a new array, but that is done by ruby

  • Creating our own classes (Bookstore App)

    • First try (using hashes)

      book_1 = {title: "Programming Ruby", pages: 360}
      • no guarentee that pages any of the fields will be defined
      • What if you wanted to add a generated summary?

    • Using a class

      class Book

  def initialize(title, pages)
    @title = title
    @pages = pages
  end

  def title
    @title
  end

  def pages
    @pages
  end

end

book_1 = Book.new "Programming Ruby", 360

puts book_1.name #=> "Programming Ruby"
puts book_1.pages #=> 360

    • Adding generated data

      class Book

  # Previous implementation omitted

  def summary
    "#{title}" is #{pages} pages
  end

end

book_1 = Book.new "Programming Ruby", 360

puts book_1.summary #=> "Programming Ruby is 360 pages"

    • Assignment methods

      class Book

  # Previous implementation omitted

  def pages=(value)
    @pages = value
  end

end

book_1 = Book.new "Programming Ruby", 360

puts book_1.summary #=> "Programming Ruby is 360 pages"

book_1.pages = 241
puts book_1.summary #=> "Programming Ruby is 241 pages"

    • Generating getters and setters

      class Book
  def initialize(title, pages)
    @title = title
    @pages = pages
  end

  def title
    @title
  end

  def title=(value)
    @title = value
  end

  def pages
    @pages
  end

  def pages=(value)
    @pages = value
  end

  def summary
    "#{title} is #{pages} pages"
  end
end

# Can be replaced with

class Book
  attr_accessor :title, :pages

  def initialize(title, pages)
    @title = title
    @pages = pages
  end

  def summary
    "#{title} is #{pages} pages"
  end
end
      • Show module, attr_reader, attr_writer, attr_accessor

    • Class vs instance methods

      • Show Array API Docs
      • :: are class methods
      • # are instance methods
      a = Array.new(3) #=> [nil, nil, nil]
a.length => 3

a.new #=> NoMethodError: undefined method `new' for [nil, nil, nil]:Array
Array.length #=> NoMethodError: undefined method `length' for Array:Class

    • Duck Typing

      • If it quacks like a duck, it must be a duck
      class Book
  attr_accessor :title, :pages

  def initialize(title, pages)
    @title = title
    @pages = pages
  end

  def summary
    "#{title} is #{pages} pages"
  end
end

class Drink
  attr_accessor :brand, :size

  def initialize(brand, size)
    @brand = brand
    @size
  end

  def summary
    "#{size} #{brand}"
  end
end

book_1 = Book.new "War, what is it good for", 360
book_2 = Book.new "The Bible", 2500
drink = Drink.new "Coke", "8 oz"

[book_1, coffee, book_2].each do |item|
  puts item.summary
end

    • Inheritance

      class Coffee < Drink
  def summary
    "Hot #{size} #{brand} coffee"
  end
end

  • Collecting summaries in a single array

    summaries = [book_1, coffee, book_2].collect do |item|
  item.summary
end

# Shorthand
summaries = [book_1, coffee, book_2].collect(&:summary)

Unix commands

  • Common unix commands

    • cd - change dir
    • mkdir - make a directory
    • rm - remove file or directory
    • touch - create a blank file
    • cat - print out a file
    • man - man pages for a command

  • ~ Your home directory

Git

  • Distributed Version Control System (DVCS)
  • Let's you track the changes you've made and allows rolling back easily
  • Used by github, Heroku.
git clone https://github.com/durango-ruby-school/Instructor-Notes.git
cd Instructor-Notes

git log

git checkout -b test

edit README

git status

git add .

git commit -m "A test commit"

git log

git push origin <BRANCHNAME>

Login to git and make pull request

Homework

  • Thoughtbot Intro to Rails - Advanced Ruby workshop
  • Code School's Try Git