クラス階層を表示するクラスメソッド

class_tree.rb

# add print class tree method to Object

class Object
  def self.print_class_tree
    @class_tree ||= {}
    # create class tree if not yet
    ObjectSpace.each_object(Class) do |cls|
      next if self == cls

      # skip is cls is no name
      next if cls.name.nil?

      # skip is cls is not self's ancestor
      next unless cls.ancestors.include? self

      @class_tree[cls.superclass.name] ||= []
      @class_tree[cls.superclass.name] << cls.name
    end if @class_tree == {}

    self._print_class_tree(self.to_s)
  end

  private
  def self._print_class_tree(arg, level=0)
    puts ('  ' * level) + arg
    return if @class_tree[arg].nil?
    @class_tree[arg].sort.each do |x|
      self._print_class_tree(x, level+1)
    end
  end
end

__END__

# example

Numeric.print_class_tree