Ruby class hierarchy

anc_desc= {}
ObjectSpace.each_object(Class).select{ |x| x < Object }.each{ |c| anc_desc[c.name] = c.superclass.name if c.name && c.superclass.name }
File.open'result.dot', 'w' do |file|
  file.puts %Q(digraph "Ruby#{RUBY_VERSION}" {\n)
  file.puts %Q(node [shape=box];\n edge [arrowtail="empty", dir=back];\n)
  anc_desc.each.sort_by { |desc, anc| anc + desc }.each{ |desc, anc| file.puts %Q("#{anc}" -> "#{desc}";\n)}
  #anc_desc.each{|desc, anc|file.puts%Q("#{anc}" -> "#{desc}";\n)}
  file.puts'}';
end
system 'dot -Tsvg result.dot -o ruby.svg'

--before in ubuntu

sudo apt install graphviz