Is it possible to call a Module function from inside a class that is also in that module

Question

In this Ruby code:

Module M
  Class C < Struct.new(:param)
    def work
      M::helper(param)
    end
  end

  def helper(param)
    puts "hello #{param}"
  end
end

I get a "undefined method 'helper' for 'M:Module'" error when I try to run

c = M::C.new("world")
c.work

but calling M::helper("world") directly from another class works fine. Can classes not call Module functions that are defined in the same Module they are defined in? Is there a way around this other than moving the class outside of the module?

Answer 1

In order to invoke M::helper you need to define it as def self.helper; end For the sake of comparison, take a look at helper and helper2 in the following modified snippet

module M
  class C < Struct.new(:param)
    include M     # include module to get helper2 mixed in
    def work
      M::helper(param)
      helper2(param)
    end
  end

  def self.helper(param)
    puts "hello #{param}"
  end

  def helper2(param)
    puts "Mixed in hello #{param}"
  end
end

c = M::C.new("world")
c.work

Answer 2

you should prepend module method with self:

module M
  class C < Struct.new(:param)
    def work
      M::helper(param)
    end
  end

  def self.helper(param)
    puts "hello #{param}"
  end
end