Following a jury trial in the Superior Court, the defendant, Charles T. Pasciuti, was convicted on indictments charging assault and battery by means of two dangerous weapons (a knife and a handgun), unlawful possession of the knife, unlawful carrying of the handgun, and unlawful possession of ammunition. The jury could have found that in the early morning hours of March 8, 1980, the victim, at the urging of Pasciuti, went to the home of one Delphine Van Tassel in Littleton, where Pasciuti robbed the victim of $200 in cash and a large quantity of controlled substances,1 and assaulted him with a knife and a loaded handgun. As a result of the incident, Miss Van Tassel was charged with being an accessory before the fact to the assaults. She was tried together with Pasciuti and entered a guilty plea while the jury were deliberating. Represented by new counsel on appeal, Pasciuti claims (1) that the judge erred in requiring trial counsel to name his witnesses to the jury venire; (2) that the prosecutor erred in withholding alleged exculpatory evidence called for by pretrial discovery; and (3) that the judge inadequately instructed the jury with respect to the withdrawal of Miss Van Tassel’s case from their consideration. We find no error and affirm the convictions.
1. After the jury venire had been sworn but prior to empanelment, the trial judge asked the attorneys to introduce themselves and to name their witnesses. The prosecutor introduced himself and identified eight witnesses for the Commonwealth. Counsel for Van Tassel introduced himself and stated that the defense witnesses would be named by counsel for Pasciuti. Pasciuti’s attorney then introduced himself and announced the names of five witnesses which included the two defendants and one witness on the prosecutor’s list. None of the named defense witnesses was ultimately called, the defense instead electing to call only a clerk from the Ayer District Court.
*835This case was tried prior to the Supreme Judicial Court’s decision in Commonwealth v. Bolduc, 383 Mass. 744 (1981). In that case, the court reversed the conviction of a defendant who was compelled, over his specific objection, to announce the names of his witnesses to the jury venire prior to empanelment. As to that situation, the court held as follows: “While we do not rule that the defendant was denied any Federal or State constitutional right, we conclude that, in fairness, proper practice does not permit requiring an unwilling defendant to announce his potential witnesses to the jury at the commencement of trial” (emphasis supplied). Id. at 747.
In the present case, however, neither defense counsel made any objection when the judge called upon him to announce his witnesses to the jury venire. Nevertheless, Pasciuti now contends (a) that the holding in Bolduc requires the reversal of his convictions despite the lack of an objection, or (b) that if an objection was required, the failure of his trial attorney to make one amounted to ineffective assistance of counsel. We reject both contentions.
The rule established in Bolduc was specifically limited to the situation where the defendant is “unwilling” to disclose his potential witnesses. We believe that the inclusion of this limiting language must be read as requiring a defendant either to make a proper objection at trial or to demonstrate on appeal circumstances which would excuse the making of such an objection.2 Ordinarily, the absence of an objection in such a situation would tend to indicate that defense counsel complied with the request as a matter of strategy or because he definitely intended to put on a defense.' Thus, particularly in cases tried prior to Bolduc, a seasonable objection would have been the only effective method of ap*836prising the trial judge that counsel wished to avoid the dilemma which might be posed by such advance disclosure. See Commonwealth v. Bolduc, supra at 747.
We recognize that the majority opinion in Bolduc appears to have left open the question whether an order requiring disclosure can be deemed to deny the defendant “any Federal or State constitutional right.” Even assuming, however, that such an order infringes upon the defendant’s right to a fair trial, we do not think that a reversal would be required if “the defendant did not sharply raise a constitutional objection” below, Commonwealth v. Moore, 379 Mass. 106, 111 (1979), in order to demonstrate his unwillingness to reveal his witnesses. Nor do we believe that any constitutional implications present in the Bolduc decision would help the defendant here, because the Bolduc rule would not appear to qualify for application to cases tried prior to the date of the decision under the specific criteria enumerated in Reddick v. Commonwealth, 381 Mass. 398, 400-402 (1980).
We therefore turn to Pasciuti’s claim that his trial counsel’s failure to object to the judge’s order deprived him of effective assistance of counsel. To demonstrate ineffective assistance, a defendant must show both (1) “that the conduct of his trial counsel fell ‘measurably below that which might be expected from an ordinary fallible lawyer,’ ” Commonwealth v. Saferian, 366 Mass. 89, 96 (1974), and (2) that “prejudice result[ed] therefrom,” Commonwealth v. Sellon, 380 Mass. 220, 223 (1980), quoting from Commonwealth v. Rondeau, 378 Mass. 408, 412 (1979). If tactical or strategic judgments are called into question, the defendant must also show that the judgment was “manifestly unreasonable,” Commonwealth v. Adams, 374 Mass. 722, 728 (1978), which typically means the loss of “an otherwise available, substantial ground of defence.” Commonwealth v. Saferian, supra.
If trial counsel’s failure to object was based on the assumption that it was proper practice to require advance disclosure of witnesses we would not deem that assumption *837unreasonable. While the practice undoubtedly was not commonplace, it did occur. Thus, prior to the clarification provided by Bolduc, it could not be expected that every lawyer would have questioned the practice. At the very least, we would not consider it ineffective assistance for a lawyer to have lacked the prescience to do so.
Moreover, our examination of the entire transcript in the case discloses that the lack of an objection may well have been based on tactical judgment. Both Pasciuti and Van Tassel were represented by reasonably experienced trial counsel. Their compliance with the judge’s order to name their witnesses could have aimed at countering any impressions made on the jury by the prosecutor’s announcement of eight witnesses for the Commonwealth. It could also have been designed to defuse the force of the prosecutor’s opening which was expected to depict a strong case against the defendants.
Further, there is nothing to indicate that defense counsel did not intend to call the witnesses named. Counsel may well have decided not to do so after the cross-examination of the victim revealed him to be a rather unsavory character whose credibility could be subject to serious doubt.3 Following that cross-examination, counsel may have thought it the wiser strategy to focus the defense on the weaknesses of the victim’s testimony, to forgo calling the witnesses originally named, and to call instead a clerk of the District Court where the drug charge against the victim was pending to confirm the nature of the charge and the unusual number of continuances that had been granted. In pursuing that strategy, counsel could also have expected that the judge’s closing instructions would minimize any adverse im*838pression which might still have lingered with the jury,4 ten days after the commencement of the trial, regarding the status of witnesses named but not called. Present counsel has also failed to show us how an objection might have changed the result in the case or contributed materially to the more than adequate defense that was furnished. See Commonwealth v. Satterfield, 373 Mass. 109, 115 (1977); Cepulonis v. Commonwealth, 384 Mass. 495, 502 (1981). We conclude, upon study of the whole record, that trial counsel’s actions did not constitute ineffective assistance and that, if counsel’s failure to object to the judge’s request was tactically grounded, his underlying judgment was not manifestly unreasonable. Commonwealth v. Adams, supra at 730. Commonwealth v. Rondeau, supra at 412. Commonwealth v. Sellon, supra at 223-226.
2. The denial of Pasciuti’s motion for a mistrial based on the alleged breach of discovery was proper.
At the outset, we emphasize that the prosecutor who prepared the case should have disclosed to defense counsel the facts that the victim had been placed in protective custody shortly after the incident, that he was still in custody at the time of trial, that he was being furnished with living expenses by the Commonwealth, and, if the prosecutor was aware of it, that there had been some discussion with Federal authorities about the victim’s being placed in the Federal witness protection program. While defense counsel may have been aware of the bare fact of protective custody, they appear not to have been aware of all the details surrounding it. We view the disclosure of the fact and details of protective custody as falling within the scope of the pretrial discovery motion filed in the case and as discoverable under Mass. R. Grim. P. 14 (a) (1) (C), 378 Mass. 874 (1979), since that information might furnish “some *839significant aid to the defendant’s case . . . [by affording a basis to] challenge[ ] the credibility of a key prosecution witness.” Commonwealth v. Ellison, 376 Mass. 1, 22 (1978).
Despite the lack of formal and full disclosure, however, all the pertinent facts were elucidated in the lengthy voir dire permitted defense counsel by the judge. These facts were also brought forcefully to the jury’s attention thereafter in cross-examination of the victim and in defense counsel’s closing arguments. “As the evidence involved here went primarily to [the victim’s] credibility, we hold that ultimate and effective presentation of the evidence to the jury cured any error that might otherwise have existed.”5 Commonwealth v. Adrey, 376 Mass. 747, 755 (1978), and cases cited. See United States v. Kaplan, 554 F.2d 577, 580 (3d Cir. 1977); United States v. Colyer, 571 F.2d 941, 948 (5th Cir.), cert. denied, 439 U.S. 933 (1978); United States v. Strahl, 590 F.2d 10, 12-13 (1st Cir. 1978), cert. denied, 440 U.S. 918 (1979).
3. The judge accepted Miss Van Tassel’s guilty plea to the accessory indictment while the jury were deliberating and thereafter instructed them as noted in the margin.6 Trial counsel for Pasciuti did not object to the instruction or request any further instructions. Appellate counsel now argues that the instruction given was deficient because it failed to caution the jury specifically that the codefendant’s *840guilty plea should not have an effect on the outcome of Pasciuti’s case. It is therefore claimed that trial counsel was ineffective because he did not object to the instruction or request additional instructions.
The judge’s instruction gave no intimation that Miss Van Tassel had pleaded guilty. Nor did the instruction imply anything improper with respect to the relationship between the withdrawal of her case from further consideration and the status of Pasciuti’s case.7 We see no basis for holding that the trial judge’s handling of the matter before the jury constituted error. See Commonwealth v. Williams, 378 Mass. 217, 228-229 (1979). Moreover, trial counsel for Pasciuti may reasonably have felt that any further embellishment of the instruction would only serve to disclose and emphasize the circumstances concerning Miss Van Tassel’s absence from the trial. See United States v. Crosby, 294 F.2d 928, 948 (2d Cir. 1961), cert. denied sub nom. Meredith v. United States, 368 U.S. 984 (1962). Since counsel was apparently content with the instruction given, we think that his failure to object or to seek further instruction also falls within the category of reasonable tactical judgment. No basis exists on the point for declaring this aspect of the defendant’s representation ineffective.
Judgments affirmed.