From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,38fc011071df5a27 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2003-06-17 10:30:29 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!headwall.stanford.edu!newshub.sdsu.edu!news-xfer.cox.net!peer01.cox.net!cox.net!news-hub.cableinet.net!blueyonder!internal-news-hub.cableinet.net!news-binary.blueyonder.co.uk.POSTED!53ab2750!not-for-mail User-Agent: Microsoft-Entourage/10.1.1.2418 Subject: Re: Ideas for Ada 200X "left hand side" repeater. From: Bill Findlay Newsgroups: comp.lang.ada Message-ID: References: <3EE7CC70.E1FD3A67@adaworks.com> <3EECA772.4B662024@adaworks.com> Mime-version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit Date: Tue, 17 Jun 2003 18:29:18 +0100 NNTP-Posting-Host: 80.195.75.181 X-Complaints-To: abuse@blueyonder.co.uk X-Trace: news-binary.blueyonder.co.uk 1055871029 80.195.75.181 (Tue, 17 Jun 2003 17:30:29 GMT) NNTP-Posting-Date: Tue, 17 Jun 2003 17:30:29 GMT Organization: blueyonder (post doesn't reflect views of blueyonder) Xref: archiver1.google.com comp.lang.ada:39350 Date: 2003-06-17T18:29:18+01:00 List-Id: On 17/6/03 17:59, in article e_GdnRh0ovFS1XKjXTWJkg@gbronline.com, "Wesley Groleau" wrote: > But it seems to me that renames covers all the "wishes" > so far except two. And it adds two: Sorry Wes, but that is not the case. I've posted the following twice before, but here goes again: > As I see it there are several arguments in favour of the 'idem' proposal: > > 1. It lets the programmer indicate that the occurrences of the LHS in the RHS > are *necessarily* the same, and not contingently so, which makes the code more > self-documenting. (Renaming does not achieve that.) > 2. It removes a source of error in transcribing the LHS multiple times. (A tie.) > 3. It allows more concisely readable code when the LHS is lengthy. (Renaming certainly does not achieve that - it requires me to write a block to 'simplify' an expression.) > 4. It provides functionality that it only partially available by means of much > clumsier renaming declarations, because not all objects can be renamed. (Obviously, renaming does not achieve that.) > 5. It requires the compiler to evaluate the lvalue of the LHS once and reuse > that lvalue as often as needed to evaluate the RHS. This has three potential > benefits: shorter code, faster execution, and once-only invocation of any side > effects. (A tie.) > 6. It might make it somewhat easier for the compiler to generate > update-in-place object code, where the target architecture allows that and > where it offers a performance advantage. (A tie?) > 7. It provides all the utility of C's multitude of combined assignment > operators with one small, compatible change to the syntax of operands. > (I specify C, rather than C++, to avoid getting into a argument about > overloading assignment). (A semantic tie, but renaming is tediously verbose for this purpose.) > 8. It allows the expression of useful forms that C's combined assignment > operators cannot achieve (e.g. X := 1 - idem;). (A semantic tie, but renaming is tediously verbose for this purpose.) My personal focus is on points 1 and 3; but I see benefits in heading off +:= and the like (points 7, 8). Renaming simply does not meet these needs. -- Bill-Findlay chez blue-yonder.co.uk ("-" => "")