Ruby: Is it possible to define a class method in a module?

Question

Say there are three classes: A, B & C. I want each class to have a class method, say self.foo, that has exactly the s

Answer 1

module Common
  def foo
    puts 'foo'
  end
end

class A
  extend Common
end

class B
  extend Common
end

class C
  extend Common
end

A.foo

Or, you can extend the classes afterwards:

class A
end

class B
end

class C
end

[A, B, C].each do |klass|
  klass.extend Common
end