220 41588 article Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Brian Bi Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: A virtual method that must *always* be overridden? 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[209.85.220.41]) by mx.google.com with SMTPS id t9sor5876940ejs.48.2019.04.04.10.35.48 for (Google Transport Security); Thu, 04 Apr 2019 10:35:48 -0700 (PDT) Received-SPF: pass (google.com: domain of bbi5291@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a17:906:4f83:: with SMTP id o3mr4473591eju.188.1554399347896; Thu, 04 Apr 2019 10:35:47 -0700 (PDT) In-Reply-To: <42fc876e-a4c7-a247-bc7f-632efbe1b28d@gmail.com> X-Original-Sender: bbi5291@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Xa9smtBC; spf=pass (google.com: domain of bbi5291@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=bbi5291@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:41588 Archived-At: --000000000000f8764e0585b7cc88 Content-Type: text/plain; charset="UTF-8" How is this different from a pure virtual method? Since foo() is not overridden in Derived, Derived is an abstract class and cannot be instantiated. By "must *always* be overridden" I had thought you meant that the definition of Derived would be ill-formed, or something like that. And was going to ask why you would ever want that. On Thu, Apr 4, 2019 at 12:18 PM Matthew Woehlke wrote: > While adding a `virtual Self* clone() = 0` to a class yesterday, I > realized something... why does C++ not have a way to mark a method that > must *always* be overridden? I'm talking about something *more* than a > pure virtual, i.e.: > > struct Root > { > virtual Root* foo() bikeshed; > }; > > struct Derived : Root > { > }; > > struct MoreDerived : Derived > { > virtual Root* foo(); > }; > > Root x; // okay > Derived y; // error: 'foo' was not overridden > MoreDerived z; // okay > > Would this be useful? > > -- > Matthew > > -- > You received this message because you are subscribed to the Google Groups > "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to std-proposals+unsubscribe@isocpp.org. > To post to this group, send email to std-proposals@isocpp.org. > To view this discussion on the web visit > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/42fc876e-a4c7-a247-bc7f-632efbe1b28d%40gmail.com > . > -- *Brian Bi* -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAMmfjbNEN_eeXk8n%3DR12uCHV3ZM9TQfgMtBdGAYqX%2B9n051g3g%40mail.gmail.com. --000000000000f8764e0585b7cc88 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
How is this different from a pure virtual method?

=
Since foo() is not overridden in Derived, Derived is an abstract= class and cannot be instantiated.

By "must *= always* be overridden" I had thought you meant that the definition of = Derived would be ill-formed, or something like that. And was going to ask w= hy you would ever want that.

On Thu, Apr 4, 2019 at 12:18 PM Matthew W= oehlke <mwoehlke.floss@gmail= ..com> wrote:
While adding a `virtual Self* clone() =3D 0` to a class yesterday, I realized something... why does C++ not have a way to mark a method that
must *always* be overridden? I'm talking about something *more* than a<= br> pure virtual, i.e.:

=C2=A0 struct Root
=C2=A0 {
=C2=A0 =C2=A0 virtual Root* foo() bikeshed;
=C2=A0 };

=C2=A0 struct Derived : Root
=C2=A0 {
=C2=A0 };

=C2=A0 struct MoreDerived : Derived
=C2=A0 {
=C2=A0 =C2=A0 virtual Root* foo();
=C2=A0 };

=C2=A0 Root x; // okay
=C2=A0 Derived y; // error: 'foo' was not overridden
=C2=A0 MoreDerived z; // okay

Would this be useful?

--
Matthew

--
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--
Brian Bi
<= /div>

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