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!feeder.eternal-september.org!aioe.org!.POSTED.3d73Ybk3C5U4I2t8lv+lAQ.user.gioia.aioe.org!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: User defined implicit conversion Date: Wed, 30 Oct 2019 23:17:05 +0100 Organization: Aioe.org NNTP Server Message-ID: References: NNTP-Posting-Host: 3d73Ybk3C5U4I2t8lv+lAQ.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:60.0) Gecko/20100101 Thunderbird/60.9.0 Content-Language: en-US X-Notice: Filtered by postfilter v. 0.9.2 Xref: reader01.eternal-september.org comp.lang.ada:57394 Date: 2019-10-30T23:17:05+01:00 List-Id: On 2019-10-30 22:26, Randy Brukardt wrote: > Implicit conversion itself is the same is eliminating strong typing. It depends, but arbitrary conversions certainly do. > If you > really want that, you probably need to use subtypes rather than types. That > is, "Type_A" should be a subtype rather than a type. > > For example, instead of: > > type Type_A is new String; > > use: > > Subtype Type_A is String; > > And now you never need to use a type conversion between Type_A and String. This is a restriction imposed by Ada 83 in order to be able to generate such null-conversions. Actually it is not null, a subtype can add a constraint and then the conversion must include constraint check. A more general case is when a subtype can have an independent representation and user-defined conversions: subtype UTF8_String is String; -- The conversion must recode Latin-1 to UTF-8 -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de