From: David Garamond <lists@...6.isreserved.com>
Date: 2004-02-01T18:30:23+09:00
Subject: check whether a class is defined, listing all classes

Given a string of fully-qualified class name, how do I easily check 
whether the class is defined or not? I hope it's not as 'hard' as I think:

  def class_defined?(classname)
    m = Class
    classname.split("::").each { |c|
      m.constants.include?(c) or return false
      m = m.const_get c
    }
    return true
  end

  p class_defined?("Test::Unit::TestCase") # false
  require 'test/unit/testcase'
  p class_defined?("Test::Unit::TestCase") # true

Is there an easier way?

A bonus question, how do I list all the defined classes in their fully 
qualified name? Example output:

  Object
  String
  FalseClass
  Struct
  Struct::Tms
  File
  File::Stat
  ...

(My own code is very ugly, I'm embarrassed to show it :-)

-- 
dave