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!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: about inheritance of subtypes and entities (such as constants) related to a type in the same package Date: Fri, 1 Jun 2018 09:56:54 +0200 Organization: Aioe.org NNTP Server Message-ID: References: <534965d3-e494-476b-8a91-6cf9f376c020@googlegroups.com> <37019e2f-b374-483a-aa62-4a76dcc568f6@googlegroups.com> NNTP-Posting-Host: MyFhHs417jM9AgzRpXn7yg.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 X-Notice: Filtered by postfilter v. 0.8.3 Content-Language: en-US Xref: reader02.eternal-september.org comp.lang.ada:52836 Date: 2018-06-01T09:56:54+02:00 List-Id: On 2018-05-31 11:10 PM, Dan'l Miller wrote: > On Thursday, May 31, 2018 at 2:59:48 PM UTC-5, Dmitry A. Kazakov wrote: >> On 2018-05-31 20:53, Dan'l Miller wrote: >>> On Thursday, May 31, 2018 at 12:37:07 PM UTC-5, Dmitry A. Kazakov wrote: >>>> On 2018-05-31 04:29 PM, Dan'l Miller wrote: >>>>> Conversely, subtyping in Ada does none of that type-extension stuff: no >>>>>  additional data/cardinality-of-the-members-of-the-set, no additional >>>>  > routines/behavior, no arbitrary refinement of behavior of overridden/copied >>>>>  routines/operations. Instead, subtyping in Ada is strictly subjecting the >>>>>  parent type to an additional membership-narrowing predicate, such as subset >>>>  > in set theory. Randy likewise spoke of membership on other branches of this >>>>  > thread. >>>> >>>> Untrue. Ada 83 subtyping extends the supertype (base type), because it >>>> exports operations defined on the subtype to the base type. Ada 83 >>>> subtyping introduces an equivalent type, which is both sub- and >>>> supertype of the base. >>> >>> If Ada83 untagged subtyping is type extension, please provide even a single characteristic that was extended/added/supplemented instead of contracted/subtracted/elided by the predicate. >> >> Elementary: >> >> subtype Extension is Integer; >> procedure Extended_Operation (X : Extension) is null; >> X : Integer; >> Y : Extension; >> begin >> Extended_Operation (X); -- See #1 >> Extended_Operation (Y); -- See #2 > > There is exactly one procedure Extended_Operation, which despite its cleverly-deceptive name is not a demonstration of type extension: We start with having a single procedure that takes X as a parameter and that is precisely where we end: no new procedure for Y, no additional storage for Y beyond Y's Xness, no new outcome in the execution of that procedure when passed a Y (except enforcement of the [unfortunately-missing] predicate as a post-condition). Interface was extended. Implementation details as to how many bodies there will be used are irrelevant. > Or in fewer words: nothing about Y is X-plus-more. There is no "more" there. > (not even a predicate to enforce, which would have made this example a tad juicier). > >> The subtype Extension extends Integer with Extended_Operation, which has >> two separate meanings: >> >> 1. The base type Integer has now a new operation: >> >> new Integer interface = old Integer interface + Extended_Operation >> >> 2. The subtype Extension extends inherited Integer's set of operations: >> >> Extended interface = old Integer interface + Extended_Operation > > Invoking the same subprogram Same to what? The interface of Integer as defined by the standard does not have Extended_Operation. How is it same? > Y merely copied some characteristics (but not others, depending on the would-be predicate) from a prior exemplar named X. You seems confuse: 1. a type with a set of values. Type = set of values + operations. Extension of a type, logically, is about adding something to any of these. 2. an extension of a type with a tagged record extension. A record extension is an extension but the reverse is wrong. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de