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!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: derived formal types and known discriminants Date: Tue, 4 Jul 2017 09:09:53 +0200 Organization: Aioe.org NNTP Server Message-ID: References: <82a59ee9-8d55-4c73-9daf-e9f7d9ab8a8f@googlegroups.com> NNTP-Posting-Host: vZYCW951TbFitc4GdEwQJg.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 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 Content-Language: en-US X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:47275 Date: 2017-07-04T09:09:53+02:00 List-Id: On 04/07/2017 02:30, sbelmont700@gmail.com wrote: > At the risk of having some of the other thread's shade thrown in > here, aren't tagged discriminated records the de facto way of doing > initialization? That is, extending a Controlled type and then using > discriminants in place of ctor arguments? Sure. I am using this quite frequently. Sometimes I go this way: type Factory_Type is record ...; type Actual_Type (Parameters : not null access Factory_Type) is tagged ...; There are obvious limitations to that. Especially that you have to keep parameters after object construction. Of course one can also do this: type Factory_Type is record ...; type Factory_Type_Ptr is access Factory_Type'Class; type Actual_Type (Parameters : Factory_Type_Ptr) is new Limited_Controlled ...; Then in the Initialize you call Unchecked_Deallocate on Parameters and comment with an appropriate number of exclamation marks that objects must be created this way: X : Actual_Type (new Parameter'(...)); Isn't getting rid of such constructs a valid argument to have proper constructors? BTW, if discriminants were abstracted as they should have been, that would be the way to implement constructors with parameters. You could declare a parameter as a public discriminant non-existing in the actual implementation and the type user would have to supply it when declaring an object. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de