220 9260 article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: add "implicit" keyword? Date: Tue, 11 Feb 2014 14:19:09 +0800 Lines: 109 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.1 \(1827\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_0F21165C-75C5-4D88-8F11-082EB40EA659" X-Trace: ger.gmane.org 1392099551 32750 80.91.229.3 (11 Feb 2014 06:19:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 11 Feb 2014 06:19:11 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBZMB46LQKGQEXJZLDRI@isocpp.org Tue Feb 11 07:19:19 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qa0-f71.google.com ([209.85.216.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WD6gg-00027N-Oc for gclcip-std-proposals@m.gmane.org; Tue, 11 Feb 2014 07:19:19 +0100 Original-Received: by mail-qa0-f71.google.com with SMTP id j5sf15186594qaq.6 for ; Mon, 10 Feb 2014 22:19:18 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=6WP1qU45dq9VuJcyMszSakiCinKFSqcwHXs8KNhMRgs=; b=fqJrYIAMjuty+RiMFkG6CyMFieUClMzY+ouZ4TWyHIxcBQ3VlhKKaa1MzjNTC4krJu 1WwiPrO+GWgq2xF/MVWvC2NwDsfSP3Wh9q1MbbxDSlxBGOYSytSL0xN8KCsFrdOUeruA 7lyEhWlowP3uBq2fk0JONip1wASC5qYBFOQL5KrQ1kGxJ+PdaFdGSDWphyu85nGBPNEw nC1QrCelykOjxC3yHqAjf17gZXsDNrUVAh3/5w/a/jXwxSTZUcRC7HuEfiJEThcXJSEU UEgBdcCSXitQbwBhPhpiRUnzkz6+H4Sl+YtJRsdEhb6FCOs8nfht8lL0+I4kDf5vRDoQ 7ycQ== X-Gm-Message-State: ALoCoQlzgdveuv0R1BDVBzB5XqQ/CsqdKI5FfCChIN6NZYoS/1Lrc+9UB3Qt4J133v3fFoQvcP7n X-Received: by 10.236.98.104 with SMTP id u68mr9940623yhf.1.1392099557948; Mon, 10 Feb 2014 22:19:17 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.73.201 with SMTP id n9ls2368352igv.13.gmail; Mon, 10 Feb 2014 22:19:16 -0800 (PST) X-Received: by 10.68.133.229 with SMTP id pf5mr42645639pbb.115.1392099556907; Mon, 10 Feb 2014 22:19:16 -0800 (PST) Original-Received: from mail-pd0-x234.google.com (mail-pd0-x234.google.com [2607:f8b0:400e:c02::234]) by mx.google.com with ESMTPS id xu6si17830129pab.167.2014.02.10.22.19.16 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 10 Feb 2014 22:19:16 -0800 (PST) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::234 as permitted sender) client-ip=2607:f8b0:400e:c02::234; Original-Received: by mail-pd0-f180.google.com with SMTP id x10so7073687pdj.25 for ; Mon, 10 Feb 2014 22:19:16 -0800 (PST) X-Received: by 10.66.233.71 with SMTP id tu7mr30505769pac.22.1392099556804; Mon, 10 Feb 2014 22:19:16 -0800 (PST) Original-Received: from [172.20.10.2] ([121.54.54.43]) by mx.google.com with ESMTPSA id si6sm128601496pab.19.2014.02.10.22.19.13 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 10 Feb 2014 22:19:15 -0800 (PST) In-Reply-To: X-Mailer: Apple Mail (2.1827) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::234 as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE 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:9260 Archived-At: --Apple-Mail=_0F21165C-75C5-4D88-8F11-082EB40EA659 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1 On Feb 11, 2014, at 1:08 AM, Matthew Woehlke wrote: > Yes, but that's the same problem as with e.g. implicit switch fallthrough= .. Some things can only work for code bases that wish to 'opt in' and thus "= have" to change their existing code (and/or live with warnings). >=20 > Currently there is no mechanism to do even that. >=20 > Also note that I explicitly specified that the meaning of existing code i= s not changed. The point is to define a common mechanism to specify intent. >=20 > The alternative is to ignore the problem or only solve it using compiler-= specific markup. Since implicit is always implicit, it can always be specified by lack of sp= ecification. Fortunately, the preprocessor provides the user with the tools= to expressively specify nothing: #define implicit // Implicit is the default, i.e. opposite of explicit keyw= ord. struct wrap_int { implicit wrap_int( int ); implicit operator int(); int value; }; This is stylistically fine, completely portable, and easy to understand (gi= ven a comment). It doesn't break anything except use of implicit as an iden= tifier, which the proposal does too. (Users would be well advised to do thi= s only after all third-party library #includes.) The only disadvantages are inability to diagnose improper usage, which isn'= t particularly important, and inconsistent syntax highlighting in text edit= ors, which savvy users can often fix for themselves. --=20 ---=20 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 e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --Apple-Mail=_0F21165C-75C5-4D88-8F11-082EB40EA659 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
On Feb 11, 2= 014, at 1:08 AM, Matthew Woehlke <mw_triad@users.sourceforge.net> wrote:

Yes, but that's the s= ame problem as with e.g. implicit switch fallthrough. Some things can only = work for code bases that wish to 'opt in' and thus "have" to change their e= xisting code (and/or live with warnings).

Currently there is no mech= anism to do even that.

Also note that I explicitly specified that th= e meaning of existing code is not changed. The point is to define a common = mechanism to specify intent.

The alternative is to ignore the proble= m or only solve it using compiler-specific markup.
Since implicit is always implicit= , it can always be specified by lack of specification. Fortunately, the pre= processor provides the user with the tools to expressively specify nothing:=

#define implicit // Implic= it is the default, i.e. opposite of explicit keyword.

struct wrap= _int {
    implicit wrap_= int( int );

<= font face=3D"Courier">    implicit operator int();

&nbs= p;   int value;
};

This is stylistically fine, completely portable, and e= asy to understand (given a comment). It doesn't break anything except use o= f implicit as an identifier, which the p= roposal does too. (Users would be well advised to do this only after all th= ird-party library #includes.)

<= /div>
The only disadvantages are inability to diagnose improper usage, = which isn't particularly important, and inconsistent syntax highlighting in= text editors, which savvy users can often fix for themselves.

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