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=ham autolearn_force=no version=3.4.4 X-Google-Thread: 103376,628d2a493f1e203d X-Google-Attributes: gid103376,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news4.google.com!border1.nntp.dca.giganews.com!border2.nntp.dca.giganews.com!nntp.giganews.com!novia!news-out.readnews.com!news-xxxfer.readnews.com!not-for-mail Date: Wed, 26 Jul 2006 20:02:53 -0400 From: "Peter C. Chapin" User-Agent: Thunderbird 1.5.0.4 (Windows/20060516) MIME-Version: 1.0 Newsgroups: comp.lang.ada Subject: Re: Subtype conformance... not what I was expecting. References: <44c6db66$0$2928$4d3efbfe@news.sover.net> <44c77cf0$0$2917$4d3efbfe@news.sover.net> <1153928329.4980.14.camel@localhost> In-Reply-To: <1153928329.4980.14.camel@localhost> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Message-ID: <44c802a7$0$2922$4d3efbfe@news.sover.net> Organization: SoVerNet (sover.net) NNTP-Posting-Host: 404472e2.news.sover.net X-Trace: DXC=GIC][InbkS=F]7I\5h`3K^<30Mb>HQXRUi>n?J8 X-Complaints-To: abuse@sover.net Xref: g2news2.google.com comp.lang.ada:5956 Date: 2006-07-26T20:02:53-04:00 List-Id: Georg Bauhaus wrote: > Let F : Person -> Room and G : Girl -> Girls_Dormitory. > Then Person -> Room is a subtype of Girl -> Girls_Dormitory (that is, > Person->Room <: Girl->Girls_Dormitory) iff Room <: Girls_Dormitory > and Girl <: Person. > > Let F : Girl -> Girls_Dormitory and G : Person -> Room. > Then Girl -> Girls_Dormitory is a subtype of Person -> Room (that is, > Girl->Girls_Dormitory <: Person->Room) iff Girls_Dormitory <: Room > and Person <: Girl. Yes, this is what I was getting at: covariance and contravariance. I think what you say above is correct. However, it is not intuitive for Room <: Girls_Dormitory or for Person <: Girl. Peter