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=-0.3 required=5.0 tests=BAYES_00, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 X-Google-Thread: 103376,ec1cbb3f01d2cff2 X-Google-Attributes: gid103376,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news1.google.com!news2.google.com!news.maxwell.syr.edu!border1.nntp.dca.giganews.com!nntp.giganews.com!newshosting.com!nx02.iad01.newshosting.com!newsfeed.icl.net!newsfeed.fjserv.net!feed.news.tiscali.de!newsfeed.freenet.de!newsfeed.arcor.de!news.arcor.de!not-for-mail From: "Dmitry A. Kazakov" Subject: Re: Direct_IO and files of tagged types Newsgroups: comp.lang.ada User-Agent: 40tude_Dialog/2.0.14.1 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Reply-To: mailbox@dmitry-kazakov.de Organization: cbb software GmbH References: <1117128009.277967.14010@g14g2000cwa.googlegroups.com> <86bcmsy3e49m.yjhfcxtf7osr.dlg@40tude.net> Date: Fri, 27 May 2005 10:38:41 +0200 Message-ID: <2nt1reaimce7.c6l18qzsap8z$.dlg@40tude.net> NNTP-Posting-Date: 27 May 2005 10:38:22 MEST NNTP-Posting-Host: 0ac05c03.newsread4.arcor-online.net X-Trace: DXC=:A\QhcJf:;YghFd\k@b23T:ejgIfPPldTjW\KbG]kaMXZmYl>WOG@=UR On Thu, 26 May 2005 18:51:47 -0500, Randy Brukardt wrote: > "Dmitry A. Kazakov" wrote in message > news:86bcmsy3e49m.yjhfcxtf7osr.dlg@40tude.net... >> On 26 May 2005 10:20:09 -0700, John McCormick wrote: >> >>> When I instantiate a version of Ada.Direct_IO with an element type that >>> is statically tagged (it is of a specific tagged type) GNAT gives me a >>> warning that the element type contains an access value. My tagged type >>> has three integer fields - no access types. I assume that the access >>> type referenced in the warning is to the tag mechanism. Any suggestions >>> for ways to create binary files of statically tagged objects? >> >> It is not a good idea to write tags into a file even if they are statically >> known, because that cannot be portable. Another general question is: if the >> tag is always known what for to have it? Without dispatching tags are just >> useless overhead! > > If the object is derived from Controlled, it will be tagged even if no > (explicit) dispatching is used. And I think that virtually all ADT types > should be controlled and extensible Right. > -- so virtually all types will have > tags. At worst the overhead is "useless" now; but that probably will change > in the future. What for? T'Class should have a tag. T should not. Provided that T is not a by-reference, limited type then there is no any good reason to put its tag into. I would really like to have *non-tagged* controlled and extensible types for which I could have T'Class. Such types could then be safely used in Direct_IO. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de