Question

module Hints
 module Designer
  def message
   "Hello, World!"
  end
 end
end

p Hints::Designer.message

Why this give me the following error…?

undefined method `message’ for Hints::Designer:Module (NoMethodError)

Answer 1

What you need to do is define message as a class method (not as an instance method). Try:

module Hints
 module Designer
  def self.message
   "Hello, World!"
  end
 end
end

puts Hints::Designer.message

If you want to use instance methods with a module, you must extend an object using the module and any given constraints (see http://ruby-doc.org/core/classes/Module.html).