helloworld.rb

module HelloWorld
  def show
    puts "Hello World!"
  end
end

puts "#{HelloWorld} is a module class."

puts "See? #{HelloWorld.class}"

puts "#{HelloWorld}'s first ancestor shows an array with #{HelloWorld.ancestors()}."

puts "Does #{HelloWorld} module include any other modules? #{HelloWorld.included_modules()}"

puts "This is how we may see the module's name HelloWorld.name() = #{HelloWorld.name()}"

puts "Is #{HelloWorld} module a singleton class? #{HelloWorld.singleton_class?()}"

# hello_world.rb:20:in `<main>': undefined method `show' for HelloWorld:Module (NoMethodError)
# p HelloWorld.show

puts "Are there any instance methods in #{HelloWorld} module? #{ HelloWorld.methods(false)}"

# Include HelloWorld module in a class
class Greeting
  include HelloWorld
  def hello
    puts show
  end
end

grtg = Greeting.new
grtg.hello

# Trying to inherit from HelloWorld module is an error.
# hello_world.rb:34:in `<main>': superclass must be a Class (Module given) (TypeError)
#class Greeting2 < HelloWorld
#  def hello
#    puts show
#  end
#end

#grtg2 = Greeting2.new
#grtg2.hello