message: Fix questionable use of a copy constructor.
diff: @@ -536,8 +536,8 @@ bool Spec::operator==(const Spec& spec) const noexcept
  case col_type_Table: {
  // Sub tables must be compared recursively
  const size_t subspec_index = get_subspec_ndx(col_ndx);
  - const Spec lhs = Spec(const_cast<Spec&>(*this).get_subspec_by_ndx(subspec_index));
  - const Spec rhs = Spec(const_cast<Spec&>(spec).get_subspec_by_ndx(subspec_index));
  + const Spec& lhs = const_cast<Spec&>(*this).get_subspec_by_ndx(subspec_index);
  + const Spec& rhs = const_cast<Spec&>(spec).get_subspec_by_ndx(subspec_index);
  if (lhs != rhs)
  return false;
  break;
  