An example irb session to learn how a piece of code that is using meta-programming works

tourist_irb_session_1.rb

wesbailey@feynman:~/playground> irb -r neverwritecodelikethis
ruby-1.9.2-p0 > space = Hash.new(0)
 => {} 
ruby-1.9.2-p0 > ObjectSpace.each_object(self.class) {|o| space[o.class] += 1}
 => 10349 
ruby-1.9.2-p0 > space.keys
 => [String, RubyToken::TkIDENTIFIER,..., NeverWriteCodeLikeThis, ... , RubyToken::TkNL, RubyToken::TkRBRACE, ArgumentError]
ruby-1.9.2-p0 > 

tourist_irb_session_2.rb

ruby-1.9.2-p0 > c = NeverWriteCodeLikeThis.new 'slug'
 => #<NeverWriteCodeLikeThis:0x00000101813128 @create_process="slug", @retrieve_process="slug", @update_process="slug"> 

tourist_irb_session_3.rb

ruby-1.9.2-p0 > c.methods.sort
 => [:!, :!=, :!~, :<=>, :==, :===, :=~, :__id__, :__send__, :class, :clone, :define_singleton_method, :display, :dup, :enum_for, :eql?, :equal?, :extend, :freeze, :frozen?, :hash, :initialize_clone, :initialize_dup, :inspect, :instance_eval, :instance_exec, :instance_of?, :instance_variable_defined?, :instance_variable_get, :instance_variable_set, :instance_variables, :is_a?, :kind_of?, :method, :methods, :nil?, :object_id, :private_methods, :protected_methods, :public_method, :public_methods, :public_send, :respond_to?, :respond_to_missing?, :send, :singleton_class, :singleton_methods, :taint, :tainted?, :tap, :to_enum, :to_s, :trust, :untaint, :untrust, :untrusted?] 

tourist_irb_session_4.rb

ruby-1.9.2-p0 > c.instance_variables
 => [:@create_process, :@retrieve_process, :@update_process] 
ruby-1.9.2-p0 > c.instance_variable_get :@create_process
 => "slug" 
ruby-1.9.2-p0 > c.instance_variables.inject({}) {|h,v| h.merge( {v=>c.instance_variable_get(v.to_sym)})}
 => {:@create_process=>"slug", :@retrieve_process=>"slug", :@update_process=>"slug"} 

tourist_irb_session_5.rb

ruby-1.9.2-p0 > NeverWriteCodeLikeThis.methods.grep /var/
 => [:class_variables, :remove_class_variable, :class_variable_get, :class_variable_set, :class_variable_defined?, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?] 
ruby-1.9.2-p0 > NeverWriteCodeLikeThis.class_variables
 => [:@@actions] 
ruby-1.9.2-p0 > NeverWriteCodeLikeThis.instance_variables
 => [] 
ruby-1.9.2-p0 > NeverWriteCodeLikeThis.class_variable_get :@@actions
 => ["create", "retrieve", "update"]