Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!uunet!uunet.UU.NET!sef From: pc@hillside.co.uk (Peter Collinson) Newsgroups: comp.std.unix Subject: Standards Update, X3J16: C++ Message-ID: <1991Jun25.214930.7804@uunet.uu.net> Date: 25 Jun 91 19:03:47 GMT Sender: usenet@uunet.uu.net (UseNet News) Organization: Hillside Systems, 61 Hillside Avenue, Canterbury, Kent CT2 8HA Lines: 302 Approved: sef@uunet.uu.net (Moderator, Sean Eric Fagan - comp.std.unix) Originator: sef@uunet.UU.NET Nntp-Posting-Host: uunet.uu.net X-Submissions: std-unix@uunet.uu.net Submitted-by: pc@hillside.co.uk (Peter Collinson) USENIX Standards Watchdog Committee Stephen R. Walli , Report Editor Report on X3J16: C++ Mike Vilot reports on the March, 1991 meeting in Nashua, New Hampshire: Current Status The ANSI X3J16 committee began its second year of technical meetings. As expected, the work grew more detailed, with the Core Language and Environment working groups being the focus of most of X3J16's work. March meeting Digital Equipment hosted the Nashua meeting. The week's major activities focused on understanding the myriad details of the proposed clarifications and changes to the current working document. X3J16's sub-groups focused on the key topics listed in the goals statement developed at the March, 1990 meeting. They worked by electronic mail between meetings, and reported their progress. International Concerns Steve Carter, of Bellcore, presented the major international concerns. Due to the concerns expressed at the November meeting about conversion to a Type I (international) X3 process, Steve came prepared with material explaining the implications of the change. To all appearances, the change seems benign to the technical work of the committee. The change would have the positive effect of getting international involvement. It has the potential to delay the development of the standard, due to the need to synchronize U.S. and ISO balloting. The full X3J16 committee almost decided to vote to adopt the change, but ran out of the quorum necessary to pass the motion on Friday morning. Editorial Jonathan Shopiro, of AT&T, presented the Editorial group's work. The most significant change from the November version was the incorporation of the exception handling proposal. Jonathan also described an editorial change that simplified the treatment of names and name lookup, merging the concepts that had previously been treated under the topics of dominance and name hiding. Martin O'Riordan, of Microsoft, questioned whether this was a purely editorial change, or a change to the language semantics. Martin and others reqeusted time to look over the change before agreeing to it. As I mentioned last time, the person who volunteered to edit the Rationale document has not been heard from since last summer. Susan Waggoner, of USWest, has taken on that responsibility. Formal Syntax James Roskind, an independent consultant, presented the work of the Formal Syntax group. The bulk of the discussion concerned a proposal by Reg Charney of Program Conversions, Inc. to rename the non- terminals in the grammar. Although there was much discussion about the virtues of regularizing the naming versus the evils of gratuitous changes, the committee decided, in the end, to adopt the proposal. Eric Krohn, of Bellcore, presented the syntactic ambiguities involving the newly-adopted throw-expression syntax for exceptions. The discussion clarified the issues, and a final resolution is likely next meeting. Tom Penello, of Metaware, gave an interesting presentation on the inherent problems with ambiguous grammars. He established the fact that an ambigous grammar makes the question of a conforming implementation undecidable. He also illustrated that arbitrary rules to resolve grammatical ambiguities has the side-effect of rejecting valid programs. He then went on to explain the syntactic ambiguities of the template syntax, arising from the conflict over using the ``>'' symbol as both a relational operator and a template argument list delimiter. Although he proposed a grammar rewrite that solved the problem, he decided not to recommend it on aesthetic grounds. There seems to be an appreciation within X3J16 as a whole for the technical issues involved in making the grammar correct. There also seems to be a sentiment in favor of letting the semantic rules settle most of the complex issues. Core Language Andy Koenig, of AT&T, presented the Core Language group's work. Document X3J16/91-0005 describes the group's discussion about the linkage of typedef names and anonymous classes. The group decided it was an Environmental issue, and handed it off to the Environment group. The group discussed objects created under a condition, and resolved to consider those objects governed by an implicit block scope, as if the programmer had explicitly supplied a compound statement. Discussion is summarized in X3J16/91- 0021. Document 91-0019 covers the discussion of lifetimes for temporary objects created by the compiler. This issue has not reached closure, although the issues were clarified. Environment Peter Chapin, of Vermont Technical College, presented the work of the Environment group. Document X3J16/91-0011 describes the group's discussion about C/C++ compatibility issues. This discussion is continuing. The group discussed at length the one definition rule - enforcing the rule that a program must have exactly one definition for a given function, even in the presence of multiple inclusions of inline functions and the potential need for the compiler to generate such functions out of line. Document X3J16/91-0024 summarizes the discussion. There is a proposal to include a section in the standard on required warnings. Laura Yaker, now at Mentor Graphics, presented some ideas of the sorts of things that might be considered as required warnings. The discussion indicated that this is a difficult issue to standardize, since there is so much variation in environments and implementations. This ongoing discussion is summarized in X3J16/91-0014. Another ongoing discussion concerns static initialization order for objects in different translation units. Document X3J16/91-0012 summarizes this discussion. There was some discussion on specifying translation limits in the standard. The discussion seemed to generate more heat than light, and nothing was decided. Lastly, the linkage of types discussion continues, and is summarized in X3J16/91-0023. Peter described several alternate rules to insure type-safe linkage of types. A central issue is whether the linkage specification is part of the type. There are interesting arguments for and against this. Libraries I presented the Library group's work. There has been some progress on formulating proposals for submission to X3J16. Aron Insinga of DEC presented his proposal to apply templates to the definition of the standard string class. His progress has been slowed by the lack of an available implementation supporting templates. Steve Clamage of TauMetric presented proposed resolutions for almost all of the compatibility issues regarding the C library. Most of the small type insecurities can be handled in a reasonably straightforward manner. There are more substantial issues regarding signals, exceptions and the facilities provided by longjmp(). The iostreams proposal continues to receive comment. Many of the UNIX-specific issues have been removed. Addressing these concerns raised an interesting point - should the C++ standard adopt the practice of the C standard, in describing only that certain 'types' exist, or should it describe them as classes and specify their required operations? There was some concern that describing classes would be inefficient, but other concerns that the vague wording without a class description would introduce too much variability among implementations. Language Extensions Bjarne Stroustrup, of AT&T, presented the work of the Extensions group. The group is working through a long list of proposals for changes to the language. A significant number of them came from the Core language group, due to an evaluation of what Andy Koenig calls for changing the wording of the standard would have the effect of changing the meaning of the language. The current list of language extension proposals includes overloading of the ``.'' operator, a proposal for handling national character set issues with digraphs and new keywords, and the adoption of the ``inherited'' keyword (as in Apple's implementation). The largest issue lurking in the Extensions category is the addition of support for run-time type information. There will be much discussion on this topic over the next months. C Compatibility Tom Plum, of Plum-Hall, presented the work of the C Compatibility group. The group continued its investigation of the vocabulary differences between C and C++. They decided to categorize their efforts into groups, covering the language, environment, and library. One likely outcome of their work will be a proposal to adopt the same model of sequence points used by X3J11. Next events The next three X3J16 1991 meetings (and their hosts) will be: o June 17-21, Lund Sweden (Lund Institute of Technology) o November 11-15, Toronto Canada (IBM) o March 1992, Austin TX (TI) Zortech announced plans to host one of the other two 1992 meetings in London. Membership on an X3 committee is open to any individual or organization with expertise and material interest in the topic addressed by the committee. The cost for membership is $250. Contact the chair or vice chair for details. Chair: Dmitry Lenkov HP California Language Lab 19447 Pruneridge Avenue MS 47 LE Cupertino, CA 95014 + 1 (408)447-5279 FAX: +1 (408)447-4924 email dmitryhpda@hplabs.hp.com Vice Chair: William M. Miller Glockenspiel, Ltd P.O.Box 366 Sudbury, MA 01776-0003 +1 (508)443-5779 email wmmiller@cup.portal.com Volume-Number: Volume 24, Number 24