220 20661 <2574e6bc-2891-4e3b-a862-d0e0210d839f@isocpp.org> article Path: news.gmane.org!not-for-mail From: Matthew Fioravante Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Bodies for inherited constructors Date: Tue, 22 Sep 2015 15:32:01 -0700 (PDT) Lines: 160 Approved: news@gmane.org Message-ID: <2574e6bc-2891-4e3b-a862-d0e0210d839f@isocpp.org> References: <89428051-95c4-486d-9e4f-1947a6cbd305@isocpp.org> <14aa5a21-b816-40f1-b6ed-b3cb0f62003d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2954_444324962.1442961121828" X-Trace: ger.gmane.org 1442961125 25467 80.91.229.3 (22 Sep 2015 22:32:05 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 22 Sep 2015 22:32:05 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDELF54RTIGRBYVNQ6YAKGQEXJ4CTWA@isocpp.org Wed Sep 23 00:32:05 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f198.google.com ([209.85.214.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZeW6W-0001qe-ER for gclcip-std-proposals@m.gmane.org; Wed, 23 Sep 2015 00:32:04 +0200 Original-Received: by obbiz7 with SMTP id iz7sf32847392obb.2 for ; Tue, 22 Sep 2015 15:32:03 -0700 (PDT) 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 :content-type: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=4vf8zDQBlewr7bOhhNU6VwwUIiBTHPwA3aVZ2wzhHhg=; b=rKOMPK9HI8jT/U5vqLr6Qt+d8wRkxUN7LnrCZJ4fdWAB0Ei3CdEckMw7O2ka5jXOxf 5cfqI+OatDxXwMQXiU+mytTNh7DYfZxC5kYwOux2j+AyKVhkI0k0ihx6pPThSsMbh5rC Y3wiom59Fhp31zgzrPMPCszi7WYTkBLw778+pwq8G+ndd0xhro2DbLGToVtiSCErSZlu d1bW0LW0ITC9q5JNQrQosOWkNJ8PeOzf3J7rPpzB74XdY1RlHP1VTqe2gu2h23yhwiXz nPATXPrhRLpSSJQnvj/R96cA3lWqcoAJPW+2YDerFRvt3SRtg22Ymnt48RSO0uvyV9jl pguw== 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:content-type: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=4vf8zDQBlewr7bOhhNU6VwwUIiBTHPwA3aVZ2wzhHhg=; b=mKyXZ2nXJunGMmR0od7ZE30+dUO1ZxHdUpSBsQaceO3bz5lK8JjtUvWJj8VkEZdCOj qd7SrDrtWg5lYN2lcFp4SxZi2wnHRNJW9S2lO4gfuqgSrXfa0ObBmhVNXzmOpg596x0C IzGnghNUJjoUDEiADvK6Y2D95W184rET5rnkAmRtDHMfJMQuwWjX3F7VfSr2+I+sfQCL eMCDxiLMK3OjGe1NjOIRM+5r+gvfMFSe4y+1Nv3d2AvKPD77CIWdPfwhDZ/AMljJvgoc MWUD350KanQsQWbnmhfBVkzxUPYvM8bbyvunF8JZXPRL7vyY1Qb0LN60GfOeO+1yhj4Z M9Eg== X-Gm-Message-State: ALoCoQnHq5CVwziNUhCpSySs/0L7v70ejR1tTrjBbYZvCbhUyNnJ24/O3Q+VU7FSSrBaXntTMwY5 X-Received: by 10.182.60.167 with SMTP id i7mr22821431obr.1.1442961123261; Tue, 22 Sep 2015 15:32:03 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.10.16 with SMTP id u16ls271641ioi.56.gmail; Tue, 22 Sep 2015 15:32:02 -0700 (PDT) X-Received: by 10.50.112.133 with SMTP id iq5mr232761igb.17.1442961122590; Tue, 22 Sep 2015 15:32:02 -0700 (PDT) In-Reply-To: <14aa5a21-b816-40f1-b6ed-b3cb0f62003d@isocpp.org> X-Original-Sender: fmatthew5876@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:20661 Archived-At: ------=_Part_2954_444324962.1442961121828 Content-Type: multipart/alternative; boundary="----=_Part_2955_1475970551.1442961121828" ------=_Part_2955_1475970551.1442961121828 Content-Type: text/plain; charset=UTF-8 On Tuesday, September 22, 2015 at 6:12:06 PM UTC-4, Giovanni Piero Deretta wrote: > > > Two solutions: > > use a separate base: > > struct A { .... }; > struct B_members { int x; B_base() : x(0) {} }; > > struct B : A, B_members { > using A::A; > }; > Clever, but if you need to mutate a member of A:: in the addon B::B logic (which my use case does) then this approach does not work since B_members won't have access to A. Essentially, I want to do this: struct A { //constructors Obj& obj(); }; struct B : A { B(/*Args*/) : A(/*forward args*/) { A::obj().do_something(); } }; > > NSMI: > > struct B : A { > using A::A; > int x = 0; > > }; > If all you need to do is initialize a data member this is the obvious solution. If you need to do something else in the constructor, this won't work. Doing your logic in a lambda meant to initialize a data member would work but it requires that B has at least 1 data member and its horribly ugly. Having an NSMI syntax for base classes could be another solution and make your B_members proposal solve my problem. -- --- 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. 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On Tuesday, September 22, 2015 at 6:12:06 PM UTC-4, Gi= ovanni Piero Deretta wrote:

Two soluti= ons:

use a separate base:

struct A { .... };
struct B_memb= ers { int x; B_base() : x(0) {} };

struct B : A, B_members {
usin= g A::A;
};
=C2=A0
Clever, but if you ne= ed=C2=A0to mutate=C2=A0a member of=C2=A0A:: in the addon=C2=A0B::B logic (w= hich my use case does) then this approach=C2=A0does not work since B_member= s won't have access to A.
=C2=A0
Essentially, I wan= t to do this:
struct<= span style=3D"color: rgb(0, 0, 0);" class=3D"styled-by-prettify"> A = {
= =C2=A0//constructors
=C2=A0Obj& obj();
};

struct B : A {
= =C2=A0B(/*Args*/) : A(/*forward args*/) { A::obj().do_something(= );= }
};

=C2=A0

NSMI:

struct B : A {
=C2=A0=C2=A0=C2= =A0 using A::A;
=C2=A0=C2=A0=C2=A0 int x =3D 0;

};
=C2=A0
If all you need to do is initialize a data member= this is the obvious solution. If you need to do something else in the cons= tructor, this won't work. Doing your logic in a lambda meant to initial= ize a data member would work but it requires that B has at least 1 data mem= ber and its horribly ugly.
=C2=A0
Having an NSMI syntax= =C2=A0for base classes could be another solution and make your B_members pr= oposal solve my problem.
=C2=A0

--

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