Question

In my project Bar, I have this class Foo, whose instances represent unique, named real-world objects. References to these instances are scattered under good care around the data structures in my project, but also, I have decided to make them accessible by their names. For this purpose, class Foo itself traces its instances, like

module Bar
  class Foo
    attr_reader :name

    def initialize( name )
      @name = name
    end

    def self.new *args, &block
      new_instance = super
      n_i_name = new_instance.name
      ( @instances ||= {} ).merge! new_instance => n_i_name
      return new_instance
    end

    def inspect; "Foo instance #{name}" end
  end
end

Now this is a common pattern. Typically, to access the instances, one can establish a public class method in Foo:

class << Bar::Foo
  def instance( i )
    case i
    when self then i
    else @instances.rassoc( i ).first end
  end
end

i = Bar::Foo.new "John Smith"
#=> Foo instance John Smith
i.object_id
#=> 68997470
Bar::Foo.instance( "John Smith" ).object_id
#=> 68997470

But the problem is, that there are analogical classes with named instances under Bar module, such as Bar::Baz, Bar::Quux and so on, which need to access Foo instances and each other by name. So I figured that keeping order in the way these various classes access each others instances by name is the responsibility of Bar module itself, and I created public module methods in it:

module Bar
  # Foo method blah blah blah...
  def self.Foo( i ); Foo.instance i end

  # Baz method blah blah blah...
  def self.Baz( i ); Baz.instance i end

  # Quux method blah blah blah...
  def self.Quux( i ); Quux.instance i end
end

Whenever classes Foo, Baz, Quux refer to each other, they use Bar.Foo( "John Smith" ) style calls, which makes possible referring to these instances also by their unique names. Now my problem is, that this still doesn’t seem 100% kosher to me. When I run rdoc to create documentation for Bar module, public class methods #Foo, #Baz, #Quux make it to the documentation. But these are not really intended to be a part of the user interface. So I have the following options, each of which has a problem:

1. Include #Foo, #Baz, #Quux in the user interface. Problem: The user does not really need them that badly; it was not my design intention to have them in UI.

2. Add # :nodoc: directive to them to prevent rdoc from documenting them. Problem: It does not feel right. It is not like Bar.Foo and friends were excluded from the user interface. It feels more like they are still part of the UI, but undocumented, secret. I don’t want that.

3. Declare them private using #private_class_method. But then, even if the instances #Foo, #Baz, #Quux access each other by name during normal operation, they, too, have to use Bar.send :Foo, "John Smith" style.

The question: The option 3. seems least harmful. But still, it is not perfect. Ideally, I would like to have methods Bar.Foo, Bar.Baz, Bar.Quux protected in such way, that these guys can call each other by names by simply calling Bar.Foo "John Smith", while the user has to use Bar.send :Foo, "John Smith", and these module methods are not documented for the user. What other options, if any, do I have to achieve this state of affairs? Is there a way to selectively allow some classes to use somebody else’s private methods at will? Also, I have no experience with protected class methods, could that be a solution? Thanks for your time spent reading this.

Answer 1

Have a look at Understanding private methods in Ruby and search SO for private/protected, there are lots of material to read.

Protected class method :

class Foo
    class << self
        def prot
            puts "self.prot"
        end
        protected :prot
    end
...

Bar::Foo.prot #=> protected method `prot' called for Bar::Foo:Class (NoMethodError)