Accessing module methods from a class in that module?

Question

Under Ruby 2.0, what is the correct way to access a module method from a class in that module?

For instance, if I have

module Foo
    class Foo
        def do_something
            Foo::module_method
        end
    end

    def self.module_method
        puts 'How do I call this?'
    end
end

I get,

./so-module.rb:7:in do_something': undefined methodmodule_method' for Foo::Foo:Class (NoMethodError) from ./so-module.rb:16:in `'

What is the correct way to define the module method so I can access it from class Foo?

Are you sure that’s the error you’re getting? I get “NoMethodError: undefined method `module_method' for Foo:Module”. — Andrew Marshall, Dec 05 '13 at 17:16
@AndrewMarshall, you're right, something was lost in translation from my actual code to simplifying it down to an example. Let me see if I can figure it out. — James McMahon, Dec 05 '13 at 17:58
Ah ok, I also had a problem with the class name being the same as the module name and that was causing weird stuff to happen, so I've corrected that. — James McMahon, Dec 05 '13 at 18:20
I actually don't get the exact same error even with a changed script, but I will update it to reflect more closely my original problem — James McMahon, Dec 05 '13 at 21:08

score 1 · Accepted Answer · answered Dec 05 '13 at 17:13

1

You have to define the method on the module’s singleton class:

module Foo
  class Bar
    def do_something
      Foo.module_method
    end
  end

  def self.module_method
    'Success!'
  end
end

Foo::Bar.new.do_something  #=> "Success!"

answered Dec 05 '13 at 17:13

Andrew Marshall

95,083
20
220
214

This also works with `Foo::module_method`. What's the difference, if any? – James McMahon Dec 05 '13 at 18:21
1

See [. vs :: (dot vs. double-colon) for calling a method](http://stackoverflow.com/questions/11043450/vs-dot-vs-double-colon-for-calling-a-method). – Andrew Marshall Dec 05 '13 at 18:30

uncutstone · Answer 2 · 2013-12-05T18:15:10.677

Please take a look at following code:

module Foo
    class Bar
        include Foo
        def do_something
            module_method
        end
    end
    def module_method
        puts 'How do I call this?'
    end
end

b = Foo::Bar.new
b.do_something

result:

How do I call this?

You can even try adding following code:

b1 = Foo::Bar::Bar.new
b1.do_something

It's tricky and has same result:

How do I call this?

Accessing module methods from a class in that module?

2 Answers2