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=-0.9 required=5.0 tests=BAYES_00,FORGED_GMAIL_RCVD, FREEMAIL_FROM autolearn=no autolearn_force=no version=3.4.4 X-Google-Thread: 103376,4ce5890331a5b529 X-Google-NewGroupId: yes X-Google-Attributes: gida07f3367d7,domainid0,public,usenet X-Google-Language: ENGLISH,UTF8 Path: g2news2.google.com!postnews.google.com!l8g2000yql.googlegroups.com!not-for-mail From: Maciej Sobczak Newsgroups: comp.lang.ada Subject: Re: Discriminants of tagged types Date: Sun, 31 Oct 2010 09:20:50 -0700 (PDT) Organization: http://groups.google.com Message-ID: References: <14314714-e92c-4036-9cbb-da8e72489261@h7g2000yqn.googlegroups.com> <3243de1d-c6b4-4845-ab5f-28ea4e9f5738@c20g2000yqj.googlegroups.com> <14f33f04-40f5-4a72-a18b-d511dd2eb3b3@w21g2000vby.googlegroups.com> <3c44f6d7-7ff0-4362-8902-fbcfe0eee788@a37g2000yqi.googlegroups.com> NNTP-Posting-Host: 85.1.63.81 Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1288542050 8873 127.0.0.1 (31 Oct 2010 16:20:50 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Sun, 31 Oct 2010 16:20:50 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: l8g2000yql.googlegroups.com; posting-host=85.1.63.81; posting-account=bMuEOQoAAACUUr_ghL3RBIi5neBZ5w_S User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8,gzip(gfe) Xref: g2news2.google.com comp.lang.ada:16022 Date: 2010-10-31T09:20:50-07:00 List-Id: On 30 Pa=C5=BA, 22:21, "Vinzent Hoefler" wrote: > > No. File descriptors are just indices into some array of objects > > managed by the operating system. > > Maybe they are, maybe they aren't. How are you supposed to know that? I've read that on Wikipedia: http://en.wikipedia.org/wiki/File_descriptor ;-) File descriptor is called a file descriptor and not just a file, because, well, it is a descriptor and not a file. > Given an opaque type, how can you tell the difference? The set of > visible operations is the same. Almost. Descriptors become dangling when the actual objects cease to exist - and this dangling state can be detected via their public interface (perhaps only via errors). The actual objects never dangle, only their descriptors (this concept includes pointers, names, etc.) can do it. > IMO polymorphism and copy semantics are distinct > concepts. As already said, I've yet to see a convincing example of a type that is both justifiably polymorphic and copyable at the same time. -- Maciej Sobczak * http://www.inspirel.com