Question

Excuse I am newbie in ruby.

My problem is about argument passes by value and reference.

I am coding this method

def show_as_tree(parents)
  array = []
  iterate_categories(parents, array)
end

def iterate_categories(parents, array)
  parents.each do |p|
    #return p.description or "-#{p.description} if the node is root or not
    p.description = category_name(p)

    #add to array
    array << p

    #call iterate categories with children of parent node and same array
    iterate_categories(p.children, array)
  end
end

however the array content is only the parent nodes.

I need understand the ruby mechanism for references and how could fix my problem?

Answer 1

I’m pretty sure Ruby just creates a copy of your array. Therefore what you should be doing is having

array << iterate_categories(p.children, new_array)

And return your array at the end of the function.

Just did a quick example: (Updating code based on Wayne Conrad’s answer… it is correct)

class Person
  attr_accessor :name, :children
end

class Test

  def iterate_categories(parents,array)
    parents.each do |p|
      array << p.name
      if !p.children.nil?
        iterate_categories(p.children,array)
      end
    end
  end

  def iterate_categories_test
    p1 = Person.new
    p1.name = "Bob"

    p2 = Person.new
    p2.name = "Joe"

    p3 = Person.new
    p3.name = "Ann"

    p4 = Person.new
    p4.name = "John"

    p1.children = [p2,p3]
    p3.children = [p4]

    array = []
    iterate_categories([p1],array)
    puts array
  end
end

Then:

>> a = Test.new
>> a.iterate_categories_test
Bob
Joe
Ann
John
=> nil

Hopefully that helps.