Create a Graphviz dot graph from all Ruby classes loaded

ruby-class-graph.rb

tree = {}

ObjectSpace.each_object(Class).each do |klass|
  # All the Errno:: classes make the graph extremely large,
  # so just collect them under a single name.
  if klass.name.start_with?("Errno::")
    ary = ["Errno::*"]
  else
    ary = [klass.name]
  end

  while klass = klass.superclass
    ary.unshift(klass.name)
  end

  hsh = tree
  while k = ary.shift
    hsh[k] ||= {}
    hsh[k][ary.first] ||= {} unless ary.empty?
    hsh = hsh[k]
  end
end

class Hash

  def recursive_each(level = 0, &block)
    each_pair do |k, v|
      block.call(k, v, level)
      v.recursive_each(level + 1, &block)
    end
  end

end

File.open("inheritance.gv", "w") do |file|
  file.puts "digraph inheritance {"

  tree.recursive_each do |k, v, level|
    v.keys.each do |name|
      file.puts("\"#{k}\" -> \"#{name}\";")
    end
  end

  file.puts "}"
end