In RoR, how do I get a subclass of my service class to recognize a class variable in its super class?

Question

I’m using Rails 4.2.5. I have this super class

class AbstractImportService

  def initialize(params)
    @init_url = params[:init_url]
  end

  private

    attr_reader :init_url

and then this class that inherits from it

class MyService < AbstractImportService

  def self.my_method(runner_id)
     puts "init_url: #{@init_url}"
     …
  end

The problem is, in the method “self.my_method,” the puts line prints out “init_url:” even if I initially the @init_url to something. Rails doesn’t have a concept of protected so is there another way I can get sub-classes to recognize class member variables of the super class?

Answer 1

@init_url = params[:init_url] is an instance variable, so you can't expect to get its value trying it to get it by self.my_method(runner_id) which is called on the MyService class (and not on an object of this class). Try with:

class AbstractImportService

  def initialize(params)
    @init_url = params[:init_url]
  end

  private
  attr_reader :init_url

end

class MyService < AbstractImportService

  def my_instance_method
    "init_url: #{@init_url}"
  end
end

2.2.1 :004 > instance = MyService.new({init_url: "http://www.example.com"})
 => #<MyService:0x007fd5db892250 @init_url="http://www.example.com"> 
2.2.1 :005 > instance.my_instance_method
 => "init_url: http://www.example.com"