variables.rb

# Fill in the values after # =>
#
$title    = "Ruby Variables"
@subtitle = "Where do they come from?"
presenter = "@tooky"

class Presentation
  @@length = "10 min"
  @style = "Code"

  def self.subtitle
    @subtitle
  end

  def self.style
    @style
  end

  def self.the_presenter
    presenter = presenter || "https://github.com/tooky"
    presenter
  end

  def self.length
    @@length
  end

  def self.title
    $title
  end

  def initialize(subtitle)
    @subtitle = subtitle
  end

  def the_presenter
    presenter = presenter || "Steve Tooke"
    presenter
  end

  def style
    @style
  end

  def length
    @@length
  end

  def title
    $title
  end
end

class Talk < Presentation
  @@length = "25 min"
  @style   = "Keynote"
end

a_presentation = Presentation.new("An instance has this effect.")
a_talk         = Talk.new("What happens with inheritance?")

$title    # =>
@subtitle # =>
presenter # =>
@style    # =>

Presentation.style         # =>
Presentation.length        # =>
Presentation.the_presenter # =>

Talk.style         # =>
Talk.length        # =>
Talk.the_presenter # =>

a_presentation.style         # =>
a_presentation.length        # =>
a_presentation.the_presenter # =>

a_talk.style         # =>
a_talk.length        # =>
a_talk.the_presenter # =>