class Rubocop::Cop::Style::AvoidPerlBackrefs

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

def on_nth_ref(node) 

def on_nth_ref(node)
  backref, = *node
  add_offence(:convention,
              node.loc.expression,
              "Prefer the use of MatchData over $#{backref}.")
  super
end