220 38142 <20180521070748.GA3811@noemi.bahnhof.se> article Path: news.gmane.org!.POSTED!not-for-mail From: Magnus Fromreide Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Better DRY when initializing members in constructor Date: Mon, 21 May 2018 09:07:48 +0200 Lines: 83 Approved: news@gmane.org Message-ID: <20180521070748.GA3811@noemi.bahnhof.se> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1526886349 24329 195.159.176.226 (21 May 2018 07:05:49 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 21 May 2018 07:05:49 +0000 (UTC) User-Agent: Mutt/1.9.2 (2017-12-15) To: std-proposals@isocpp.org, Raymund Hofmann Original-X-From: std-proposals+bncBDELLREETMBRBR7ARHMAKGQERWGMHSI@isocpp.org Mon May 21 09:05:45 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f72.google.com ([209.85.215.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fKet3-0006Bq-HA for gclcip-std-proposals@m.gmane.org; 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[130.236.254.3]) by mx.google.com with ESMTPS id o7-v6si5945688lja.29.2018.05.21.00.07.51 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 21 May 2018 00:07:51 -0700 (PDT) Received-SPF: pass (google.com: domain of magfr@lysator.liu.se designates 130.236.254.3 as permitted sender) client-ip=130.236.254.3; Original-Received: from mail.lysator.liu.se (localhost [127.0.0.1]) by mail.lysator.liu.se (Postfix) with ESMTP id 914AF4002D; Mon, 21 May 2018 09:07:50 +0200 (CEST) Original-Received: from noemi.bahnhof.se (h-155-4-132-137.NA.cust.bahnhof.se [155.4.132.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.lysator.liu.se (Postfix) with ESMTPSA id CEB6340008; Mon, 21 May 2018 09:07:49 +0200 (CEST) Mail-Followup-To: std-proposals@isocpp.org, Raymund Hofmann Content-Disposition: inline In-Reply-To: X-Virus-Scanned: ClamAV using ClamSMTP X-Original-Sender: magfr@lysator.liu.se X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of magfr@lysator.liu.se designates 130.236.254.3 as permitted sender) smtp.mailfrom=magfr@lysator.liu.se 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:38142 Archived-At: On Sun, May 20, 2018 at 10:53:02PM -0700, Raymund Hofmann wrote: > initializing members via the constructor repeats the type two times plus a > variable name three times: > > struct S > { > int i; > const char* cp; > S(int i, const char* cp) : i(i), cp(cp) {} > }; > > I was trying to find a way improving on this. > > The best i could come up with was something like: > > struct T > { > struct I > { > int i; > const char* cp; > } m; > T(const I& i) : m(i) {} > }; > > usage: > > void testf() > { > S s(1, "abc"); > T t({ 1,"abc" }); > } > > Are there already some proposals/ideas for improving DRY on this? > > My Idea: > > I could think of a different class definition something like "lambda > capture style": > > struct U (i=int(0); *cp="123") // <- "capture list" > { > // members which are initialized to a fixed value don't go in the > "capture list", use regular members > // capture list generates a constructor to initialize the members implied > by the "capture list" > // usual class members/functions go here... > }; > > usage: > > void testf() > { > U u(3,{}); > } > > The generated constructor should also be available to delegate to, so > additional constructors can be had if desired. > Maybe there is a better idea for integrating this "capture style" > initialization nicer and more compact when using it as a delegate. > In C++-14 you can write struct V { int i = 0; const char* cp = "123"; }; V v1; V v2 { 2, "234" }; Is that terse enough for you? /MF -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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