code: def def_ivar_delegator(ivar, alias_ = ivar, **kwd)
        prefix, suffix, wrap = prepare_delegate(**kwd)
  
        if suffix
          alias_ = alias_.to_s.gsub(
            /\?$/, ""
          )
        end
  
        class_eval delegate_debug(<<-STR), __FILE__, __LINE__ - 9
          def #{alias_.to_s.gsub(/\A@/, "")}#{suffix}
            #{wrap}(
              #{prefix}#{ivar}
            )
  
          rescue Exception
            if !Forwardable.debug && $@ && $@.respond_to?(:delete_if)
              $@.delete_if do |source|
                source =~ %r"#{Regexp.escape(__FILE__)}"o
              end
            end
  
            raise
          end
        STR
      end
docs: ------------------------------------------------------------------------
   Delegate a method to an instance variable.
   ------------------------------------------------------------------------