Can a restriction on cross-examination be sustained on the basis of the discretion of the trial court?

Respondent urges that the restriction can be sustained on the basis of the trial court's discretionary power to limit unreasonable cross-examination, citing People v. La Macchia, supra, 41 Cal.2d at page 743, 264 P.2d 15. However the record shows that such was not the basis of the court's decision. The court repeatedly deferred a ruling on this point because of its importance and because of the difficulty in finding conclusive authority as to the extent to which offers could be used in cross-examination as distinguished from direct examination and finally ruled such evidence out because it had been shown that the expert had not learned of any offers. It must be noted here that the La Macchia case, now the leading case on the matters here involved was decided after the judgment appealed from. 'If a ruling which might have been made as a matter of discretion is based entirely upon other grounds, the appellate court will not consider whether the ruling would constitute a proper exercise of the discretionary power.' 5 C.J.S., Appeal and Error, 1583, p. 474. Here the rulings were clearly made as matters of law, of admissibility, not as matters of discretion and we must review their correctness as such. Compare 5 C.J.S., Appeal and Error, 1586 p. 477.