220 38737 <17d39779-2bb9-4073-ab3f-4b14eef2d0de@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Charles Salvia Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal for generic rebind template Date: Tue, 19 Jun 2018 14:57:35 -0700 (PDT) Lines: 155 Approved: news@gmane.org Message-ID: <17d39779-2bb9-4073-ab3f-4b14eef2d0de@isocpp.org> References: <824bd50b-55f9-4ca5-b17f-db5ba21245dd@isocpp.org> <7f5b55e9-e935-421a-b0ab-3b5cbbb1c624@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_26529_1560161599.1529445456186" X-Trace: blaine.gmane.org 1529445333 28311 195.159.176.226 (19 Jun 2018 21:55:33 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 19 Jun 2018 21:55:33 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDY6DLOFSEPBBUPYUXMQKGQEBI2X6AY@isocpp.org Tue Jun 19 23:55:29 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 1fVOb1-0007F6-5g for gclcip-std-proposals@m.gmane.org; Tue, 19 Jun 2018 23:55:27 +0200 Original-Received: by mail-yb0-f197.google.com with SMTP id q12-v6sf661522ybp.11 for ; Tue, 19 Jun 2018 14:57:38 -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=kvOLCrcG54bz6wZ61L+s886B9vL87d7rxhBj09pbcSk=; b=aRBLMH7hTLj01hOcM6NWb8wRhls9JUH0e7YcZNubp6NwkwUBKGtXamEgnhBtQmZbgf 234xRD9aIkzXyLJlNQhkl8RfBmFWKmcaP2/MgdkFfcRG7oUtH4hAAk6IhWp7fBskOWQY jCu8/UgeWZBhWfuhN5wvqrgjypyFHO+p/Fe2J3uO3hXdwVEcpikGGPPmt8tM6eQH9fak yvc32jzCt9h0KNGJ2LltHYFOrhG+Vc36Jkix9beMhSzzbW4rEI0c/tOtXg8g4MS/Cq09 tmuZ7z/5pqkgTV6Y+EgGpi8Sx7IJpsnQ0EiblrbSVu9PMvTcyUTKJHYqVX/4xiiNQ+Ax +DZw== 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=kvOLCrcG54bz6wZ61L+s886B9vL87d7rxhBj09pbcSk=; b=Bwlti/Z78WZzE/8EeKvY8kS9lVIdP42Ar5R9AUvdtWrvwxwbBS6/wEaeuFaXrzhqh+ Jk9DQN6LldvNnrKEdSQxH2ORdjBXGRjEznjF//5EKX9ZL68b9QH0KRixonp+jPdLPGWI 47TrE/ObSideQIXxwlTzHo0VCNZjJzqChSSUxnZD70PnZPNM9Wy4a1kRpFcaDvCGHIy7 ixyQFrORmZuc+wSP0y4uFnGbRB2HeTZjygTzNnNQVEwUlG797ZaWKAarSJyPacC/GlMz nVB5j7A+aBpa53NpkQk0BomUOLT7Ag+e+bERtjnQ08+xWfRM5EC0exmav+bN1qEMZg4J yQRg== 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=kvOLCrcG54bz6wZ61L+s886B9vL87d7rxhBj09pbcSk=; b=A9IVNv1SanS0nFslHS2pr3xKY9NCCWxI0pjUJnuIrb4sZ0JfI4BaLSxChPxo/nVf6e 0NfxhhT/cNaf2HiSVBaAxq+1IAoExzDmpUFflKNbGOzYo2olVx2X1AkjHmKHIjHkl3bG zd8HQfqwvB147xIJCIU+U8qLoTkdcIKFmzAYhAR2ooFwM33EZb5DTJOt+lbs5+B7bs6Q BDpDm5Z8SyofwCmbjnZdLswb0miqxNVu9xizcgnC4Efvyy5B+hdrnIxAlKcAp/wh9GqR /NEi/tj9tO5JFMkWj96i0intk/dvxVvQmvGsmuNNcnjMfsjUWiAwyxR2mqAqM1XVSsIq VxAA== X-Gm-Message-State: APt69E0ff/1D0wCScGntDZR3z1BTp94VMpBfgw/GgJiLeEAyob5ZBUBe Bd1xtozIP+oWAsHvFe12mgm6Jg== X-Google-Smtp-Source: ADUXVKL1yzUHF6hcgbXnxsJyetfwKtgwIkJfYWycOfj82984GgaruwjAmiNYBD/kIWw2abkVVGDvjA== X-Received: by 2002:a25:5d08:: with SMTP id r8-v6mr5114570ybb.64.1529445458102; Tue, 19 Jun 2018 14:57:38 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:44c:: with SMTP id 73-v6ls204625ybe.11.gmail; Tue, 19 Jun 2018 14:57:37 -0700 (PDT) X-Received: by 2002:a5b:10c:: with SMTP id 12-v6mr210060ybx.1.1529445456835; Tue, 19 Jun 2018 14:57:36 -0700 (PDT) In-Reply-To: <7f5b55e9-e935-421a-b0ab-3b5cbbb1c624@isocpp.org> X-Original-Sender: charles.a.salvia@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:38737 Archived-At: ------=_Part_26529_1560161599.1529445456186 Content-Type: multipart/alternative; boundary="----=_Part_26530_1758866658.1529445456187" ------=_Part_26530_1758866658.1529445456187 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Right. In that case it wouldn't do the expected thing, because=20 std::pmr::vector is defined as an alias template rather than a class=20 template. On Tuesday, June 19, 2018 at 1:20:10 PM UTC-4, Arthur O'Dwyer wrote: > > On Monday, June 18, 2018 at 9:03:12 AM UTC-7, Charles Salvia wrote: >> >> *Updated draft proposal for generic rebind template:* >> >> http://charles-salvia.github.io/CPP-REBIND-PROPOSAL.html >> >> Implementation files: >> >> https://github.com/charles-salvia/std-proposal-generic-template-rebind= =20 >> >> >> This is a proposal to create a generic mechanism for rebinding template= =20 >> parameters (std::rebind_t), to remove the need for ad-hoc rebind templat= es,=20 >> such as std::allocator_traits::rebind_alloc, etc.=20 >> > > This is a bad idea for several philosophical reasons (and I say that as= =20 > the presenter of this talk =20 > on a similar subject. The difference is that I don't want any "generic"= =20 > rebind facility, I just want a greater number of special-purpose rebinder= s). > > However, your idea doesn't work anyway. Try it on some library types: > > using V =3D std::pmr::vector; > using W =3D rebind_t; > static_assert(std::is_same_v>); // error= ! > > Since it's a bad idea *and* doesn't work, I think you should give it up. > > However, it's also much easier to implement as a pure library extension= =20 > than you thought it was. I can do it in 28 lines and I bet it can be done= =20 > in fewer. > https://wandbox.org/permlink/pRIQ8lJaf8irznwK > > =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/17d39779-2bb9-4073-ab3f-4b14eef2d0de%40isocpp.or= g. ------=_Part_26530_1758866658.1529445456187 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Right.=C2=A0 In that case it wouldn't do the expected = thing, because std::pmr::vector is defined as an alias template rather than= a class template.

On Tuesday, June 19, 2018 at 1:20:10 PM UTC-4, Ar= thur O'Dwyer wrote:
On Monday, June 18, 2018 at 9:03:12 AM UTC-7, Charles Salvia wrot= e:
Updated draft= proposal for generic rebind template:


<= /div>
Implementation files:


This is a proposal to create a generic mech= anism for rebinding template parameters (std::rebind_t), to remove the need= for ad-hoc rebind templates, such as std::allocator_traits::rebind_al= loc, etc.=C2=A0

This is a bad i= dea for several philosophical reasons (and I say that as the presenter of <= a href=3D"https://www.youtube.com/watch?v=3D0MdSJsCTRkY" target=3D"_blank" = rel=3D"nofollow" onmousedown=3D"this.href=3D'https://www.youtube.com/wa= tch?v\x3d0MdSJsCTRkY';return true;" onclick=3D"this.href=3D'https:/= /www.youtube.com/watch?v\x3d0MdSJsCTRkY';return true;">this talk on= a similar subject. The difference is that I don't want any "gener= ic" rebind facility, I just want a greater number of special-purpose r= ebinders).

However, your idea doesn't work any= way. Try it on some library types:

=C2=A0 =C2=A0 u= sing V =3D std::pmr::vector<int>;
=C2=A0 =C2=A0 using W =3D= rebind_t<V, double>;
=C2=A0 =C2=A0 static_assert(std::is_s= ame_v<W, std::pmr::vector<double>>); =C2=A0// error!
=

Since it's a bad idea and doesn't= work, I think you should give it up.

However, it&= #39;s also much easier to implement as a pure library extension than you th= ought it was. I can do it in 28 lines and I bet it can be done in fewer.

=E2= =80=93Arthur

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/17d39779-2bb9-4073-ab3f-4b14eef2d0de= %40isocpp.org.
------=_Part_26530_1758866658.1529445456187-- ------=_Part_26529_1560161599.1529445456186-- .