# used by munge function to safely interpolate
# $1, $2, etc. into the replacement string
sub _safeswitch {
  my %seen;
  @seen{@+} = (undef) x @+;
  my @P;
  {
    no strict 'refs'; # allow $$_ to be $1, $2, etc.
    no warnings 'unitialized'; # allow undef as $$_
    @P = map { $$_ } undef, 1 .. scalar keys %seen;
  }
  $_[0] =~ s/\$(\d+)/$P[$1]/g;
  $_[0];
}