220 37206 article Path: news.gmane.org!.POSTED!not-for-mail From: Richard Hodges Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: General purpose utilities for template metaprogramming and type manipulation Date: Sun, 4 Mar 2018 11:58:12 +0100 Lines: 203 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="94eb2c060312f0de050566941567" X-Trace: blaine.gmane.org 1520160974 9850 195.159.176.226 (4 Mar 2018 10:56:14 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 4 Mar 2018 10:56:14 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD4PBM7UWAHRBRNC57KAKGQES3MMIGQ@isocpp.org Sun Mar 04 11:56:10 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f197.google.com ([209.85.223.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1esRJI-0001k3-Kz for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id l76sor5973438ioi.364.2018.03.04.02.58.13 for (Google Transport Security); Sun, 04 Mar 2018 02:58:13 -0800 (PST) Received-SPF: pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.107.23.131 with SMTP id 125mr13145332iox.130.1520161092851; Sun, 04 Mar 2018 02:58:12 -0800 (PST) Original-Received: by 10.2.102.105 with HTTP; Sun, 4 Mar 2018 02:58:12 -0800 (PST) In-Reply-To: X-Original-Sender: hodges.r@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=LlhoGmWx; spf=pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=hodges.r@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=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:37206 Archived-At: --94eb2c060312f0de050566941567 Content-Type: text/plain; charset="UTF-8" For my part, while I think the general idea is a good one, it seems to me that you will make a stronger argument if you are able to provide motivating use-cases to strengthen the argument for each type/template. Do you have some examples? On 4 March 2018 at 07:55, Vincent Reverdy wrote: > Hey, > > I was starting to think about putting together a proposal to add minor > helper classes to either type_traits/utility/tuple to help with some of the > operations done again and again when doing template metaprogramming. > Here is a list of a few I can think of, but I would have liked to hear > other suggestions. Names are just indicative, and bikeshedding would happen > for all of these types. > > > - *std::blank*, defined as an empty struct > struct blank{}; > - *std::pack*, to hold a parameter pack of type > template struct pack{}; > - *std::convertible*, a type convertible to anything > struct convertible{template constexpr operator T() const > noexcept;}; > - *std::copy_qualifiers*, a type traits copying ref and cv qualifiers > from one type to another > template struct copy_qualifiers {using type = /* > cv-ref qualfiers of From applied to To*/;}; > > Other suggestions? > > -- > 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. > To view this discussion on the web visit https://groups.google.com/a/ > isocpp.org/d/msgid/std-proposals/e3415a75-7e20-48dd- > 9e24-0e4681f46e53%40isocpp.org > > . > -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CALvx3hacsACYSq%2Bh7BHNCjZ2rpajbdcBxa8GigKuHnjO79YDyQ%40mail.gmail.com. --94eb2c060312f0de050566941567 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
For my part, while I think the general idea is a good one,= it seems to me that you will make a stronger argument if you are able to p= rovide motivating use-cases to strengthen the argument for each type/templa= te.

Do you have some examples?



O= n 4 March 2018 at 07:55, Vincent Reverdy <vince.rev@gmail.com> wrote:
Hey,

= I was starting to think about putting together a proposal to add minor help= er classes to either type_traits/utility/tuple to help with some of the ope= rations done again and again when doing template metaprogramming.
Here i= s a list of a few I can think of, but I would have liked to hear other sugg= estions. Names are just indicative, and bikeshedding would happen for all o= f these types.

  • std::blank, defined as an empty struct=
    struct blank{};
  • std::pack, to hold a parameter pack of = type
    template <class... T> struct pack{};
  • s= td::convertible, a type convertible to anything
    struct convertible{template = <class T> const= expr operator T() con= st noexcept;};
  • std::copy_qualifiers, a type traits copying ref and cv qualifie= rs from one type to another
    template <class <= span style=3D"color:#606" class=3D"m_6942501654450711629styled-by-prettify"= >From, class To> struct copy_qualifiers {using type =3D /* cv-ref qualfiers of From ap= plied to To*/;};

Other suggestions?

--
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