question.rb

# Please note: this is an oversimplification of the real problem :)

# Say you have this class definition:

class One
  attr_accessor :children

  def initialize data
    puts "Initialize One"
    @children = data.map do |item|
      item = Two.new(item)
    end
  end
end

class Two
  attr_accessor :children

  def initialize data
    puts "Initialize Two"
    @children = data.map { |item| item = Three.new(item) }
  end
end

class Three
  attr_accessor :data

  def initialize data
    puts "Initialize Three"
    @data = data
  end
end

# Now I create a new instance of the One class:
data = [["foo", "bar"], ["foo", "bar"]]
myOne = One.new(data)

# I can now do this:
puts myOne.children.first.children.first.data # "foo"

# Now my question is: how would I access class One methods from class Three?
# i.e: imagine I need to access the @children property of class One from a
# method in class Three. What would be a good way to do that, other than passing
# a 'parent' parameter to every class constructor in the chain?
# 
# Thanks in advance!
# 

I have Document -> Pages -> Layers, so I guess that counts as "naturally hierarchical". I actually started doing the "pass a reference back to the parent" part, but then I thought that maybe Ruby already had something like object.parent and didn't feel like reinventing the wheel.

Thanks a lot : )

"passing a reference back to the parent object might be a fine solution."

Yes, but this can also be fixed by following the design patterns more closely.

Seems 2 and 3 are models (containing data), where he want to add some logic to 3 that's doing more than related to his model, that should be moved to a controller class.

A controller class should known the structs of the models and be able to make all links, anyway, as quick solution, passing a reference is a fine solution indeed.

In which case does a Layer need to know on what Page he is on?