gistfile1.rb

class Module
  # Return all constants presently defined
  def all_constants
    # I <3 you ActiveSupport, really I do!
    if defined?(ActiveSupport::Deprecation)
      ActiveSupport::Deprecation.silence { __all_constants }
    else
      __all_constants
    end
  end
  
  #######
  private
  #######
  
  # Actual implementation of all_constants method
  def __all_constants
    result = {}
    parents = [self.class]
    
    until parents.empty?
      unprocessed_parents = parents
      parents = []
      
      unprocessed_parents.each do |parent|
        parent.constants.each do |constant_name|
          constant = begin
            parent.const_get constant_name 
          rescue Exception
            # Some packages (i.e. Rack) apparently try to automagically
            # pull in gems when you frob their constants.  The bastards.
            # Sometimes ActiveSupport likes to freak out as well.  If we 
            # encounter errors when frobbing constants, just ignore them
            # and carry on.  And yes, "rescue Exception" is necessary there
            next
          end
          
          next unless constant.is_a? Module
          next if result.include? constant
        
          result[constant] = true
          parents << constant
        end
      end    
    end
    
    result.keys
  end
end

class Class
  # Return all descendants of a class
  def descendants
    if defined?(ActiveSupport::Deprecation)
      ActiveSupport::Deprecation.silence { __descendants }
    else
      __descendants
    end
  end
  
  #######
  private
  #######
  
  def __descendants
    all_constants.select { |obj| obj.ancestors.include? self }
  end
end