passing child class method as function argument in ruby

There is a class Commerce and its constructor will initialize an object named commerce. LineItem is a class with in the Commerce class. LineItem class has a method named "ssm". when this method "ssm" is invoked it will initialize an object of another class named SSM. In our problem, we need pass to the "ssm" method as a function argument in another Test class.

 def autoUpdate(docNum, type, varName, value)
   type = method(Commerce::LineItem:ssm)
  commerce.line_item.type.call(varName).set(value)
end

In the place of the function parameter 'type', it should be replaced by different method names from the class LineItem. However the above function autoUpdate throws an error. How to pass child class methods as function parameters in another class.