class RuboCop::Cop::Style::PerlBackrefs

backreferences like $1, $2, etc.
This cop looks for uses of Perl-style regexp match

def autocorrect(node) 

def autocorrect(node)
  lambda do |corrector|
    backref, = *node
    parent_type = node.parent ? node.parent.type : nil
    if [:dstr, :xstr, :regexp].include?(parent_type)
      corrector.replace(node.source_range,
                        "{Regexp.last_match(#{backref})}")
    else
      corrector.replace(node.source_range,
                        "Regexp.last_match(#{backref})")
    end
  end
end

def on_nth_ref(node) 

def on_nth_ref(node)
  add_offense(node, :expression)
end