220 20089 article Path: news.gmane.org!not-for-mail From: Bengt Gustafsson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Should GCD/LCM take variable numbers of arguments? Date: Thu, 27 Aug 2015 01:53:24 -0700 (PDT) Lines: 142 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_192_584032461.1440665604607" X-Trace: ger.gmane.org 1440665629 8438 80.91.229.3 (27 Aug 2015 08:53:49 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 27 Aug 2015 08:53:49 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCRIRSPDTQIRBBNA7OXAKGQE3VXH4DA@isocpp.org Thu Aug 27 10:53:34 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZUsw3-0008Sg-KY for gclcip-std-proposals@m.gmane.org; Thu, 27 Aug 2015 10:53:27 +0200 Original-Received: by iodt126 with SMTP id t126sf85836131iod.0 for ; Thu, 27 Aug 2015 01:53:26 -0700 (PDT) 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=DyzcqCYxJf7eBPjqnPG3cyzRwjc5uWapQddOr0QCqLk=; b=RYI+Wh4UY13rNjbdg9z/0+/8/lqg+mjhHIfRX68DALGuptQlFssvGpej3zbRXUW2zF 9DuWkjnXAtUhlcvrY2QiqGfAJ70rQO63vjylKIH1guzN/vXL6K/TfW4YrF17iSGFB8tz iPD3ar+93/7gpHxzGuJXLk+OdeKIMfpc8AeNOTHVlZBmWeBmu8j8k+Q8i/Cb8rSViqwy eeqGZ/fL8A8xunkcQMhs0TVm14au1jxvMsbuH/S+UgqimZj3kL8Eli4XE3Hf/QUqQVbe 9tTI4hmWCn8Ioml+aRw8M3HGqt7qDQEFydApysa5/M8l0HdFkNDCnD7YCRspXmpDgoy2 KqXQ== X-Gm-Message-State: ALoCoQnT7DSoX0MwhgZmNXdOXHM0cpykV+DEUazYrVnCFkPK5kr4hw/f7cLNCmV9Qm+HiMbdClKW X-Received: by 10.182.117.225 with SMTP id kh1mr3533522obb.12.1440665606639; Thu, 27 Aug 2015 01:53:26 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.56.111 with SMTP id z15ls388638igp.35.gmail; Thu, 27 Aug 2015 01:53:25 -0700 (PDT) X-Received: by 10.50.111.43 with SMTP id if11mr216346igb.1.1440665605684; Thu, 27 Aug 2015 01:53:25 -0700 (PDT) In-Reply-To: X-Original-Sender: bengt.gustafsson@beamways.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:20089 Archived-At: ------=_Part_192_584032461.1440665604607 Content-Type: multipart/alternative; boundary="----=_Part_193_1002446060.1440665604607" ------=_Part_193_1002446060.1440665604607 Content-Type: text/plain; charset=UTF-8 I think this is a good idea. It should also be available for std::min and std::max and possibly others. In C++11 we got min and max for initializer_list instead. Checking the reason for this may reveal objections to a variadic template solution that apply to gcd and lcm as well. As for the return type, why not just use auto except for the 2 parameter case? Den onsdag 26 augusti 2015 kl. 21:42:36 UTC+2 skrev Myriachan: > > On Saturday, August 22, 2015 at 9:51:09 PM UTC-7, Daryle Walker wrote: >> >> I recently saw descriptions of GCD and LCM as part of the Library >> Fundamentals v2 paper (N4529), the original paper (N4601), and >> cppreference.com. I'm wondering if those functions should take variable >> numbers of arguments. I mean like: >> >> >> constexpr T gcd(T x); // returns |x| >> >> constexpr common_type_t gcd(T x, U y); // current definition >> >> constexpr common_type_t gcd(T x, U y, V z, W ...a); // >> returns gcd(x, gcd(y, z, a...)) >> >> >> // And similar for "lcm" >> >> >> Good idea?... >> >> > That seems reasonable; implementations could potentially have a faster > version for multiple inputs if they wanted. > > I'm wondering about what the return type ought to be, though. > gcd(INT_MIN, 0) == -INT_MIN, which would be undefined if the return type is > int. Perhaps make_unsigned_t> ? > > I don't know whether it's worthwhile, but we could define gcd and lcm for > zero and one parameter as well. gcd() == 0, lcm() == 1 I suppose; gcd(x) > == x and lcm(x) == x, obviously. > > Melissa > -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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I think this is a good idea. It should also be available f= or std::min and std::max and possibly others. In C++11 we got min and max f= or initializer_list<T> instead. Checking the reason for this may reve= al objections to a variadic template solution that apply to gcd and lcm as = well. As for the return type, why not just use auto except for the 2 parame= ter case?


Den onsdag 26 augusti 2015 kl. 21:42:36 UTC+2 skrev M= yriachan:
On Saturday, August 2= 2, 2015 at 9:51:09 PM UTC-7, Daryle Walker wrote:
I recently saw descriptions of GCD and LCM a= s part of the Library Fundamentals v2 paper (N4529), the original paper (N4= 601), and cppreference.com. I= 'm wondering if those functions should take variable numbers of argumen= ts. I mean like:

<typename T>=
constexpr T gcd(T x); =C2=A0// returns |x|<typename T, typename U= >
constexpr common_type_t<T, U> gcd(T x, U y); =C2=A0// current definition
<typename = T, typename U, typename V, <= span style=3D"color:#606">typename... W>
constexpr common_type_t<T, U, V, W...> gcd(T x, U y, V z, W ...a); =C2= =A0// returns gcd(x, gcd(y, z, a...))


// And similar for "l= cm"


Good idea?...=


That seems reasonable; imp= lementations could potentially have a faster version for multiple inputs if= they wanted.

I'm wondering about what the return type ought to = be, though.=C2=A0 gcd(INT_MIN, 0) =3D=3D -INT_MIN, which would be undefined= if the return type is int.=C2=A0 Perhaps make_unsigned_t<common_type_t&= lt;T, U, V, W...>> ?

I don't know whether it's wo= rthwhile, but we could define gcd and lcm for zero and one parameter as wel= l.=C2=A0 gcd() =3D=3D 0, lcm() =3D=3D 1 I suppose; gcd(x) =3D=3D x and lcm(= x) =3D=3D x, obviously.

Melissa

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