Ruby class to build and print a class hierarchy.

class_hierarchy.rb

class ClassHierarchy

  def initialize(root_class)
    @root_class = root_class
    @parent_class = @root_class.superclass
    @tree = {}
    generate_tree
  end

  def to_s
    @tree.collect { |class_name, subclasses| branch_to_s class_name, subclasses }.join
  end

private

  def generate_tree
    subclasses.each { |subclass| subclass.insert_into_tree @tree, @parent_class }
  end

  def subclasses
    @subclasses ||= all_classes.select { |klass| klass < @root_class }.collect { |klass| ClassHierarchy::Subclass.new klass }
  end

  def all_classes
    @all_classes ||= ObjectSpace.each_object(::Class)
  end

  def branch_to_s(class_name, subclasses, indent=0)
    string = (" " * indent)
    string << class_name
    string << "\n"
    string << subclasses.collect { |subclass_name, subsubclasses| branch_to_s subclass_name, subsubclasses, indent + 2 }.join
  end

  class Subclass < Struct.new(:subclass)

    def superclasses
      @superclasses ||= subclass.ancestors - subclass.included_modules
    end

    def insert_into_tree(tree, root_class)
      classes = superclasses.take_while { |klass| klass != root_class }
      classes.reverse.collect(&:name).compact.inject(tree) { |memo,name| memo[name] ||= {} }
    end

  end

end

gistfile1.txt

> Dir[File.join Rails.root, "/app/controllers/*"].each {|file| require file }
> puts ClassHierarchy.new ActionController::Base
ActionController::Base
  ApplicationController
    UsersController
    UserSessionsController
    OrdersController
    ...

I used this class in our project and I added sorting because the tree looked rather chaotic without it:

   def branch_to_s(class_name, subclasses, indent=0)
     string = (" " * indent)
     string << class_name
     string << "\n"
-    string << subclasses.collect { |subclass_name, subsubclasses| branch_to_s subclass_name, subsubclasses, indent + 2 }.join
+    string << subclasses.sort.collect { |subclass_name, subsubclasses| branch_to_s subclass_name, subsubclasses, indent + 2 }.join
   end