Why does singleton methods of a module not inherit?

Ruby
1

working as expected

class Foo
@@x = 12
def self.bar
p @@x
end
end

class Bar < Foo
end

Bar.bar # => 12

I am having some hard time to understand why the below code is not
working, while the above.

module Foo
@@x = 12
def self.bar
p @@x
end
end

class Bar
include Foo
end

Bar.bar # undefined method bar’ for Bar:Class (NoMethodError)

2

Hi.

Basically, when you include a module, you make the module’s methods
available to objects of the resulting class. A class-level or
module-level method must be used on the class or module directly. As you
do not “inherit” from a module but either include it or extend an object
with it, you should not expect the class Bar to react as if it had
inherited from any other class.

Also, you do not create a singleton in your example-code.

sing = Bar.new.extend(Foo)

  • creates a singleton ‘sing’

What you want is this:

lose self

module Foo
def bar
p 12
end
end

extend the class directly

class Bar
extend Foo
end

  • extends the class Bar with the module Foo. Try that instead. You will
    be surprised… :wink:

Cheerio.

P.S.: I do not like metaprogramming. Modules, to me, are a way to create
“Polymorphism” in Ruby.