From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on ip-172-31-74-118.ec2.internal X-Spam-Level: X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.5-pre1 Path: eternal-september.org!reader02.eternal-september.org!aioe.org!5WHqCw2XxjHb2npjM9GYbw.user.gioia.aioe.org.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: array from static predicate on enumerated type Date: Mon, 15 Mar 2021 21:25:10 +0100 Organization: Aioe.org NNTP Server Message-ID: References: <89128f73-fcc5-4e57-8067-d09877ba0211n@googlegroups.com> <6ca041f3-2669-4497-9548-2f17666702a6n@googlegroups.com> <26c44e00-a899-455a-a929-1e23c7935fe3n@googlegroups.com> <9abb081d-a323-466d-9ae8-a2fc8fa24725n@googlegroups.com> NNTP-Posting-Host: 5WHqCw2XxjHb2npjM9GYbw.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; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 Content-Language: en-US X-Notice: Filtered by postfilter v. 0.9.2 Xref: reader02.eternal-september.org comp.lang.ada:61539 List-Id: On 2021-03-15 18:48, Shark8 wrote: > So, in Ada, there's no good choice for how to actually DO an array with gaps in the index: That applies to all containers. The problem is mapping the key to a dense position when the key is not dense or might be unordered. There is no gaps in positions. > But Array *isn't* a map, though often it is substituted as one. Of course it is, per definition of mapping. f : key -> element. > Array has further constraints, like the contiguous memory labeled above. No. The constraint here is a dense index. That is not specific to a general map or an array. It is a fundamental property of the set of keys being a convex set. Convex ensures certain useful mathematical properties invariant to the representation of the mapping. In particular, it gives a way to enumerate elements. If you want to enumerate non-convex keys of a map you have a problem. As the OP just encountered. Arbitrary predicate kills convex, so the problem. Not array. A map would have just same problem: a map of LETTERS is in general not substitutable for a map of CURVED_LETTERS. > Ada's arrays ARE contiguous memory; so I'm not sure what you're trying to distinguish here. No. A dense index allows contiguous representation, but it does not require it. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de