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=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!news.unit0.net!news.mixmin.net!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Why stack can hold indefinite objects but records cannot? Date: Tue, 28 Nov 2017 21:46:59 +0100 Organization: Aioe.org NNTP Server Message-ID: References: NNTP-Posting-Host: MajGvm9MbNtGBKE7r8NgYA.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 Content-Language: en-US X-Notice: Filtered by postfilter v. 0.8.2 Xref: reader02.eternal-september.org comp.lang.ada:49222 Date: 2017-11-28T21:46:59+01:00 List-Id: On 2017-11-28 21:31, Victor Porton wrote: > Why is it OK to create an indefinite object as a local variable ("on stack") > but not OK to put an indefinite object into a record? It is OK in both cases. You must provide the constraint that is. > By the way, how indefinite local variables can be implemented? (just > curious) They cannot, there is no such thing. A variable can hold a value which constraints vary. Each value is constrained. These either deploy a maximum allocation length like bounded strings or hidden referential semantics like unbounded strings. > Moreover, wouldn't it to be a good idea to allow indefinite objects in > records (thus making the record itself indefinite, even if it has no > discriminants)? It is a bad idea because there is no straightforward implementation of. The proper solution is to have an abstract record interface which would allow anything appear a record member whereas the implementation would be left to the user. The compiler should provide simple implementation of that out of the box, maybe even less than it does already. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de