220 39177 article Path: news.gmane.org!.POSTED!not-for-mail From: Arthur O'Dwyer Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Concepts requires clause should allow types that constexpr implicitly convert to bool? Date: Sun, 15 Jul 2018 15:48:10 -0700 (PDT) Lines: 96 Approved: news@gmane.org Message-ID: References: <79029827-71df-4af1-ae50-607e96c5e322@isocpp.org> <0f77fb8d-5058-47e9-b1ec-519958786893@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_48556_996312867.1531694890424" X-Trace: blaine.gmane.org 1531694765 31762 195.159.176.226 (15 Jul 2018 22:46:05 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 15 Jul 2018 22:46:05 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDLZJYWNDQIKXHVP3ICRUBC7HE3VG@isocpp.org Mon Jul 16 00:46:01 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f197.google.com ([209.85.213.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fepmD-0008AV-B9 for gclcip-std-proposals@m.gmane.org; Mon, 16 Jul 2018 00:46:01 +0200 Original-Received: by mail-yb0-f197.google.com with SMTP id q12-v6sf32794965ybp.11 for ; Sun, 15 Jul 2018 15:48:12 -0700 (PDT) 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 :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=+RXiWz9bV/KCa897XKDNvZ18jsRH98XMyJ1GU7MyQGw=; b=KttH/56tqGYH+zCQTHqDxYfwfCsjDJrndS/qwCAsqLYTivSBllorPiIqW761jYALoL T318lJi2a0sUATxMKsp444JMlkbZSvnsr3dFV5LD/emM/VI7kles9mq7XyRLPZqZrSLD vn6tUVGXAvtF99Y8qP8ezaLD3imOsNA21pYfhIR4WU3kuX5HKi+uIckF9gdKBkPDG9Jg kn+qD/JuE+k6ibkj7K4xaQdqd9GM8uJ6WEkIjBIi3qbEHp7EjXvedBJpvTyydPLBRjWH SxZ045vt/bUm5Gvroi4rEx29TSsxU+uN7E7tLaBBj0CZi7F2TmPJPw/FCZLGZ0ZwjnDL 9pBQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=+RXiWz9bV/KCa897XKDNvZ18jsRH98XMyJ1GU7MyQGw=; b=F/9HaO/QVxyp7L/wbZiJX97BfEbNyF9+jDeB1tskuqsFI2uwrMVGn9XFHD2WnDIz4X dN6DNN3mg8wO0Yva1Du/OFCgyCSYZ+pE28c377kuEV+XYIrOQHO9opE5rY40xZbzs7CP Zqp94CI5HWGHjV90Q/Zp2FfPMsCTtWJYMwbDrcWaSIity7daUlhkFoIc4p4/Gat9znV2 PAEgnYeBiu9KikLkr7WJBDJZowHJdOEiOxS/RheFKDb/oya4yfN1haxlbrEz8vrsgwVe M0zD9LsnRtAMuXmPS6c/dwj5GjLioeJBSe/xnYpVTT4lDGoJMk0wa6H3+UBPU/oXZNNC JDQw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; 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=+RXiWz9bV/KCa897XKDNvZ18jsRH98XMyJ1GU7MyQGw=; b=f4rEo9ni13zKG8KDLw/4Mcxk2lr+YffHkPvsxhrbaoDBit8Zp3KmccoLXn8Mj3WK2k gLMjrDRPTn6RY851O0Q3+aBnJV+n+xSj5AMsURS9ztbQE0DXVLsav6SssnGzVBrgpXIC 4EsTSD+n+aQHxYNpGudwTKENrW2C6+dbkIO7vAIDUXx04Jwwsr208O30Ak1/dqniVQlz xkq9lBj82+KX9lSOZ6X2ukit+E0qEjpuksYg59COKXYvI/yapfjX/hKdiwLX7n41LSax CijUOPxvmCc1u7ws85qHEPuJm7/ZmBnhLKKZ0bxNZ6ZMS1m6hcTvi+CB3ihcVKHPatDS 5L+w== X-Gm-Message-State: AOUpUlE/acpwq9LV41FUhB/xqWl8Q/yGceUnb6DPD8kP0oFyYRnTwaCm zbgjCdqXMytwMTIQ8NcQ1Zs8Vw== X-Google-Smtp-Source: AAOMgpdsgGQCboy4Cx6dzoBWqAS151GAwh27wFnA1F66sqRwwWroRotHxfuu/QL1LHUS0BuCvWjIdg== X-Received: by 2002:a81:1786:: with SMTP id 128-v6mr4927324ywx.176.1531694891979; Sun, 15 Jul 2018 15:48:11 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:4181:: with SMTP id o123-v6ls8360528yba.21.gmail; Sun, 15 Jul 2018 15:48:11 -0700 (PDT) X-Received: by 2002:a25:8203:: with SMTP id q3-v6mr1803048ybk.1.1531694890824; Sun, 15 Jul 2018 15:48:10 -0700 (PDT) In-Reply-To: <0f77fb8d-5058-47e9-b1ec-519958786893@isocpp.org> X-Original-Sender: arthur.j.odwyer@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:39177 Archived-At: ------=_Part_48556_996312867.1531694890424 Content-Type: multipart/alternative; boundary="----=_Part_48557_902166159.1531694890425" ------=_Part_48557_902166159.1531694890425 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sunday, July 15, 2018 at 3:44:52 PM UTC-7, Arthur O'Dwyer wrote: > > Another easy workaround would be to change the word `auto` to `bool`. > I would expect requires(x) to follow exactly the same rules as=20 > noexcept(x). If it doesn't, that's a bug in my book. > And IIUC, your original code is equivalent to template constexpr bool is_even =3D (v % 2 =3D=3D 0); template requires is_even int some_function() { return (v * 3); } int main () { std::cout << some_function<4>() << '\n'; } is that right? The integral_constant stuff just seems unnecessarily=20 confusing to me. =E2=80=93Arthur --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/abe8f0c5-5a08-4301-b26a-871f4abacdab%40isocpp.or= g. ------=_Part_48557_902166159.1531694890425 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Sunday, July 15, 2018 at 3:44:52 PM UTC-7, Arthur O'= ;Dwyer wrote:
= Another easy workaround would be to change the word `auto` to `bool`.
I= would expect requires(x) to follow exactly the same rules as noexcept(x). = If it doesn't, that's a bug in my book.

And IIUC, your original code is equivalent to
template<auto v&= gt;
constexpr bool i= s_even =3D (v % 2 =3D=3D 0);

template<auto v>=C2=A0requires is_even<v><= /span>
int some_function()
{
=C2=A0 return (v * 3);
}

int main ()
{
=C2=A0 std::cout << some_function&= lt;4>() << '\n';
}
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