220 24875 <245e65c5-c96d-4366-b616-814606d4ebe9@isocpp.org> article Path: news.gmane.org!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Go-like embedding Date: Wed, 2 Mar 2016 05:46:28 -0800 (PST) Lines: 215 Approved: news@gmane.org Message-ID: <245e65c5-c96d-4366-b616-814606d4ebe9@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_6304_1134666666.1456926388582" X-Trace: ger.gmane.org 1456926397 27885 80.91.229.3 (2 Mar 2016 13:46:37 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 2 Mar 2016 13:46:37 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBNO53O3AKGQECH4JREY@isocpp.org Wed Mar 02 14:46:37 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f199.google.com ([209.85.214.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ab76q-0005pu-OJ for gclcip-std-proposals@m.gmane.org; Wed, 02 Mar 2016 14:46:37 +0100 Original-Received: by mail-ob0-f199.google.com with SMTP id rt7sf45173491obb.0 for ; Wed, 02 Mar 2016 05:46:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=3n7nQYsL+8TDXm1QjMJUJIkJM5D56jDORtF0KsOuj6U=; b=jNZ2hZS2U0EFgOA0A+iCUfsrAGTmegMEX7lFn2GIj8/Ohts+KorCv23dRlmPtUUVV/ us5LKndFvRZxDS3ytSeGR8WcD3yvi/0L+MwOtv22TpqQE9mKkT2tWA8wmZsM13vNN+kL KcXjk7mFRDCo/qbHeiRd5Viq8ufpHLhKZZ2iNxYKxcovISCOZuwegAHUZKKWjzV2G1Cz fjJba+wQQk29HNWzCg8MyxdUUITknjMDwNBomnzspbQdxu7MrB2GmQSI2GbaGOahE46A 8pxIua6G6Ee0MkY7St/oLGMIRRyhetN0oIZtXAL6lQSOvp7C0EVF8hB0ktYSqBNkITiR ktgA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=3n7nQYsL+8TDXm1QjMJUJIkJM5D56jDORtF0KsOuj6U=; b=BsI3qBho97FvbMfZW67p4UZJN2VUrDBY2/HH7qRnutJPhMRKOh4JCqoE80NlxU9Mt8 YyvAKPVCt0L86Mu78Vs59GbzYkXh7vL5kwMDX8tYiy+Z9MJmzVB/ij2t+i8xgPKoJ4oo Dt0YVPnKbQtL54PuN2BKveFZ3kOB0zJA0XjLpMGS8RqpPqDLKOMLUQ93as+m93h+9x/C evCPW52Z//RhbCQMQt6SvHY1fW9aXABmipWbAD+JSPv0EhxRw38BaZnaG1coQtbYic8v WylqMarhudMU72UqiqNqsEUYRL3lvGa6snnSauYk5Mt86IYeiuNnDgcfNVNfsnrgRyvV vE3A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=3n7nQYsL+8TDXm1QjMJUJIkJM5D56jDORtF0KsOuj6U=; b=DnrL76aBOFFGnoKItNElhmBr3JlY4ALaitAjIl0v5DO9SCkZz3uR3zs4SjFQ8LukoQ 8are7Qiv6gZLZ/qRzoivM7uGdT7XDvBbD2FYBDsXJCxpmaC7gbkOQu8ChlrIZDS2yd2e vp16y+S1x21A6ekJPdGDCrq55G4xg6nOkU9XgGze0J9a0Kgk1k8pGVKULpVVVuALVDaY K3kpDIT+EjUz7F1anEOcPUxG8fPxbo2M+5ywn5+tTQHUQEdPJV+4YslZa9zQS/VRBIV1 DkDGw8MBStv5mnF/S4WwQlUvr/Jbsh/Y7x6YC6Tv2cZiJ/VTyJpa+L10klSH9+JyE4cf Irfw== X-Gm-Message-State: AD7BkJIJG51rSOUTOLzomqctpOnZ2aapMmGioM6Zndf6/AnM+V0XokBELb/4BEVcgvMBZg== X-Received: by 10.50.87.7 with SMTP id t7mr3538840igz.11.1456926390667; Wed, 02 Mar 2016 05:46:30 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.47.154 with SMTP id v26ls2190758iov.91.gmail; Wed, 02 Mar 2016 05:46:29 -0800 (PST) X-Received: by 10.50.73.234 with SMTP id o10mr121734igv.10.1456926389490; Wed, 02 Mar 2016 05:46:29 -0800 (PST) In-Reply-To: X-Original-Sender: jmckesson@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:24875 Archived-At: ------=_Part_6304_1134666666.1456926388582 Content-Type: multipart/alternative; boundary="----=_Part_6305_1116270529.1456926388583" ------=_Part_6305_1116270529.1456926388583 Content-Type: text/plain; charset=UTF-8 On Wednesday, March 2, 2016 at 8:27:30 AM UTC-5, NeoCode wrote: > > In Go programming language, there is a feature named "emedding", which is > used instead of classic c++-like inheritance. > For example: > > type SmallBox struct { > a, b, c int > } > type BigBox struct { > Timestamp time.Time > SmallBox // <<< embedding > Name []string > } > > This is very simple and low-level extension of the concept of > inheritance; the programmer explicitly specifies the location of the base > object in the successor. It is strange that this simple and obvious > opportunity not appeared in the C language. > > I propose enhanced (compared with Go) feature of such embedding. We can > use the existing "inline" keyword (or some other keyword, eg. "embed") to > indicate the embedded fields. > > struct SmallBox { > int a, b, c; > }; > > struct BigBox { > time_t Timestamp; > inline SmallBox inlinedBox; > std::string Name; > }; > > As a result, we can access to the fields of SmallBox both directly and > through an intermediate name "inlinedBox": > > BigBox box; > box.a = 10; //directly, like inheritance > box.inlinedBox.b = 10; // using an intermediate name, like aggregation > > > .... what's wrong with inheritance? I know people tend to believe that using inheritance for something like this is wrong, but these cases are *exactly* why C++ has robust support for multiple inheritance, unlike most languages. -- 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/245e65c5-c96d-4366-b616-814606d4ebe9%40isocpp.org. ------=_Part_6305_1116270529.1456926388583 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Wednesday, March 2, 2016 at 8:27:30 AM UTC-5, NeoCode w= rote:
In Go pr= ogramming language,=C2=A0there is a feature named "emedding",=C2= =A0which is used instead of classic c++-like inheritance.
For example:
type SmallBox struct {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 a, b, c int
}
type BigBox struct {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Timestamp time.= Time
=C2=A0 =C2=A0 =C2=A0 =C2=A0 SmallBox = =C2=A0// <<< embedding
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Name []string
}
This is very simple and low-level extension of the concept of inheritance= ;=C2=A0the programmer explicitly specifies the location of the base object = in the successor.=C2=A0It is strange that this simple and obvious opportuni= ty not appeared in the C language.

I propose= enhanced (compared with Go) feature of such embedding.=C2=A0We can use the= existing "inline" keyword (or some other keyword, eg. "embe= d") to indicate the embedded fields.

struct SmallBox {
=C2=A0 int a, b, c;
};

struct BigBox {
=C2=A0time_t Timestamp;=
=C2=A0inl= ine Sma= llBox inlinedBox;
=C2=A0std::string Name;
};

As a result, we can access to the fields of=C2=A0SmallBox= =C2=A0both directly and through an intermediate name "inlinedBox"= :

BigBox box;
box.a =3D 10; = //directly, like inheritance
box.inlinedBox.b =3D 10; // using an in= termediate name, like aggregation



..= .. what's wrong with inheritance? I know people tend to believe that usi= ng inheritance for something like this is wrong, but these cases are exa= ctly why C++ has robust support for multiple inheritance, unlike most l= anguages.

--
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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/245e65c5-c96d-4366-b616-814606d4ebe9= %40isocpp.org.
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