Question

Is it possible to declare static methods in a module in ruby?

module Software
  def self.exit
    puts "exited"
  end
end

class Windows
  include Software

  def self.start
    puts "started"
    self.exit
  end
end

Windows.start

The example above will not print out “exited”.

Is it only possible to have instance methods in a module?

Answer 1

Define your module like this (i.e. make exit an instance method in the module):

module Software
  def exit
    puts "exited"
  end
end

and then use extend rather than include

class Windows
  extend Software
  # your self.start method as in the question
end

In use:

irb(main):016:0> Windows.start
started
exited
=> nil

Explanation

obj.extend(module, …) adds to
obj the instance methods from each module given as a parameter

…so when used within the context of a class definition (with the class itself as the receiver) the methods become class methods.