220 24339 <7e08b6c5-853c-471e-b248-a9df7e8e27be@isocpp.org> article Path: news.gmane.org!not-for-mail From: Arthur O'Dwyer Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: [tuple] extracting tuples out of a tuple Date: Fri, 12 Feb 2016 16:28:12 -0800 (PST) Lines: 458 Approved: news@gmane.org Message-ID: <7e08b6c5-853c-471e-b248-a9df7e8e27be@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1234_442185814.1455323292521" X-Trace: ger.gmane.org 1455323301 7702 80.91.229.3 (13 Feb 2016 00:28:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 13 Feb 2016 00:28:21 +0000 (UTC) Cc: mwoehlke.floss@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDLZJYWNDQIJ34PZWUCRUBDCYD4DM@isocpp.org Sat Feb 13 01:28:16 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f199.google.com ([209.85.213.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aUO4N-0000bt-4I for gclcip-std-proposals@m.gmane.org; Sat, 13 Feb 2016 01:28:15 +0100 Original-Received: by mail-ig0-f199.google.com with SMTP id rs1sf75130454igb.3 for ; Fri, 12 Feb 2016 16:28:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc: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=Tb5buHCWNoPTeWjLjOrudplp69Wga/vDlWf9sR7TOHk=; b=UNIzUgb7+YYwByaVDZB4WS49zc9h4xI62PLZsqTYXmP/XHX8V195QdgzwPz0Wgmbdy 6JzIWCebx11thL19Iei/dF+KpiS/bYRTf1c+dMq4XlOuTMTQVy8ghn4lGW7TOETL+DZ1 0NyAXK1gpmPAeYjvfw5wCzgB6ZaQKnj1l4k8C5pTCYr603BvZZwwYwh0TK0c9HVyX0Yw BiOxiBi/hWkJ22MqRTthMv8C8LbEqW4nneU94UiyODAgEd4nm0imzUpwD9pdkvmNU2Dv mC4uc/az7sa9ZlDmMkpQsyrT0vSzFnVjXzO1vN+TkZiA1MxdDt4Xylq9nI+kjawq7Mii fNJw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc: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=Tb5buHCWNoPTeWjLjOrudplp69Wga/vDlWf9sR7TOHk=; b=wZX16QfQukm+AyzOdOrFKnT0mVoGIMQ2QzpgmFSOCCAnPD0xH8vCz+Iw2kRFW/lX1V ew1v7YSm9HQYxZeW+6cf9RPB8pabyAfOMxwOORjaVGyVdMnGa6t1/vdoml7pQl7Cj6s+ pJxFzK0GKBI0SY/Wv2HL5TzA7DRr1Bfn7s0LxBFvsYy6cB40gyXuPiKIVd0rs6Yao563 TLsY/WPoD5t7W9LEagIVUh464yIWBBl58fTun6yIwYhoeh2+Az+MTsX6CCzkPnwkZiND 8MJK9aWTYjvbMc3pLnYNrIx8IF18BjH3rUTqAu8WrkqY3zwglghffKjxc8P6US1WapAG qWcw== 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:cc: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=Tb5buHCWNoPTeWjLjOrudplp69Wga/vDlWf9sR7TOHk=; b=mhNp+q0a17MMpnnfwYn6TVkvws9R53zyR7RGBBibLTkV+hm08V1qneHI9iSNzUNJMJ hktZxWHJrZihay/pxGcpNXrOyWWiBkKJQ8rqkQBlSPns44qCCNS1p0e0C+xhy80Lvvmk ZJXqwuhLDq2FBi88Euu8SvsCHmjOeHwX+Kv/db/jBffqqZiGXzEjTHK4Sw8yjXF2rC1k WBnyOmPRjZytu6f2/HLdT4UyG7F23/VsgwQWkOxWRhN0D3iniwRqowEeR5WYuqRDdg8R SekMxxjlYj+RMV9UYw1aBS8RmfCnLawkXpkNJfMfx5WL+/hoD3KtTMLczDSRnxI3nO5M SabQ== X-Gm-Message-State: AG10YOTMUhLby3fYmKA9COhTAHS8fiv4avhNc8K/6axRfyDMwmBjI4zF4K/XXTRR7/uHRA== X-Received: by 10.182.28.41 with SMTP id y9mr4455179obg.14.1455323294291; Fri, 12 Feb 2016 16:28:14 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.64.179 with SMTP id p19ls290297igs.0.gmail; Fri, 12 Feb 2016 16:28:13 -0800 (PST) X-Received: by 10.50.61.200 with SMTP id s8mr9552igr.3.1455323293113; Fri, 12 Feb 2016 16:28:13 -0800 (PST) In-Reply-To: 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:24339 Archived-At: ------=_Part_1234_442185814.1455323292521 Content-Type: multipart/alternative; boundary="----=_Part_1235_1903403071.1455323292523" ------=_Part_1235_1903403071.1455323292523 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Friday, February 12, 2016 at 9:11:35 AM UTC-8, Matthew Woehlke wrote: > > On 2016-02-12 11:30, Oliver Kowalke wrote:=20 > > 2016-02-12 16:06 GMT+01:00 Matthew Woehlke >:=20 > >> I'm not a fan of using magical references to do indirect assignment,= =20 > >> i.e. any of your proposals, but especially `split`. All of these seem= =20 > >> backwards, i.e. should be `tpl1 =3D head<3>(tpl);` instead.=20 > >=20 > > I've had std::tie() in mind,=20 > >=20 > > int i...;=20 > > X x...;=20 > > std::tie( i, x) =3D get_tuple();=20 > > That's also a horribly ugly interface that we shouldn't be perpetuating;= =20 > http://wg21.link/p0144 solves that exact example ever so much better...= =20 > I think maybe Oliver was trying to say that tuple tpl { -1, "abc", "xyz", .5 }; tuple tpl1; tpl1 =3D tail(tpl); // Python: tpl1 =3D tpl[1:] tail(tpl) =3D tpl1; // Python: tpl[1:] =3D tpl1 should both work, because tail() should return a tuple of references=20 instead of a tuple of values. I definitely support=20 not-making-unnecessary-copies in general, and particularly in this case if= =20 it lets tail() work like tie(). But it does seem a little bit=20 non-orthogonal. (Also, I'm assuming that Oliver made some typos in his=20 original post =E2=80=94 notice I've flipped the "tpl" and "tpl1" in the sec= ond line=20 above.) Also, of course, head(x) should logically return get<0>(x), not some weird= =20 synonym for reverse(tail(reverse(x))). But that's just poor naming. The=20 underlying operation here is either "splice" (extract a contiguous range of= =20 indices from the input tuple, as in the Python above) or "select" (extract= =20 a noncontiguous set of indices from the input tuple and compress them, as= =20 in various vector instruction sets). I agree that std::tuple< int, std::string, std::string, double > tpl{ -1, "abc",=20 "xyz", .5 }; std::tuple< int, std::string, std::string > tpl1; std::tuple< std::string, double > tpl2; split( tpl1, tpl2) =3D tpl; is just nonsense, as written. However, under the "unpacking with postfix tilde" not-a-proposal, a similar= =20 operation could be written like this: tuple tpl { -1, "abc", "xyz", .5 }; tuple tpl1; tuple tpl2; std::tie(tpl1~..., tpl2~...) =3D tpl; assert(std::get<0>(tpl1) =3D=3D std::get<0>(tpl)); assert(std::get<1>(tpl1) =3D=3D std::get<1>(tpl)); assert(std::get<0>(tpl2) =3D=3D std::get<2>(tpl)); assert(std::get<1>(tpl2) =3D=3D std::get<3>(tpl)); In general, I think that the C++ standard library is woefully lacking in=20 tuple manipulators... but rather than proposing new tuple manipulators (of= =20 which there could be a million: zip, fold, map, car, cdr, reverse,...), we= =20 should be trying to give people the ability to express those manipulators= =20 natively in the language, via something like Matthew's [:] notation or my= =20 ~... notation. my $.02, =E2=80=93Arthur --=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 https://groups.google.com/a/isocpp.org/group/std-propos= als/. ------=_Part_1235_1903403071.1455323292523 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Friday, February 12, 2016 at 9:11:35 AM UTC-8, Matthew = Woehlke wrote:
On 2016-02-12 11= :30, Oliver Kowalke wrote:
> 2016-02-12 16:06 GMT+01:00 Matthew Woehlke <mwoehlk...@gmail.com>:
>> I'm not a fan of using magical references to do indirect a= ssignment,
>> i.e. any of your proposals, but especially `split`. All of the= se seem
>> backwards, i.e. should be `tpl1 =3D head<3>(tpl);` inste= ad.
>=20
> I've had std::tie() in mind,
>=20
> int i...;
> X x...;
> std::tie( i, x) =3D get_tuple();

That's also a horribly ugly interface that we shouldn't be perp= etuating;
http://wg21.link/p0144 s= olves that exact example ever so much better...

I think maybe Oliver was trying to say= that

=C2=A0 =C2=A0 tuple<int, string, string, double= > tpl { -1, "a= bc",<= /span> "xyz", .5 };
=C2=A0 =C2=A0 tuple<string, string, double> tpl1;
=C2=A0 =C2=A0 tpl1 =3D tail(tpl); =C2=A0 =C2=A0// Python: tpl1 =3D tpl[1:]
=C2=A0 =C2=A0 tail(tpl) =3D tpl1= ; =C2=A0 =C2=A0// Python: tpl[= 1:] =3D tpl1


sh= ould both work, because tail() should return a tuple of references instead = of a tuple of values. I definitely support not-making-unnecessary-copies in= general, and particularly in this case if it lets tail() work like tie(). = But it does seem a little bit non-orthogonal. =C2=A0(Also, I'm assuming= that Oliver made some typos in his original post =E2=80=94 notice I've= flipped the "tpl" and "tpl1" in the second line above.= )

Also, of course, head(x) should logically return= get<0>(x), not some weird synonym for reverse(tail(reverse(x))). But= that's just poor naming. The underlying operation here is either "= ;splice" (extract a contiguous range of indices from the input tuple, = as in the Python above) or "select" (extract a noncontiguous set = of indices from the input tuple and compress them, as in various vector ins= truction sets).

I agree that

<= div class=3D"prettyprint" style=3D"background-color: rgb(250, 250, 250); bo= rder: 1px solid rgb(187, 187, 187); word-wrap: break-word;">
=C2=A0 =C2=A0 std::tuple< int,<= /span> std= ::string, std::string, double <= /span>>= tpl{ -1, &q= uot;abc", "xyz"= , .5 };
=C2=A0 =C2=A0 std::tuple< int<= /span>, std::string, std::string > tp= l1;=
=C2=A0 =C2=A0= std::tuple< std::string, double > tpl= 2;<= span style=3D"color: #000;" class=3D"styled-by-prettify">
=C2=A0 =C2=A0 = split( tpl1, tpl2) =3D tpl;

is just nonsense,= as written.
However, under the "unpacking with postfix tild= e" not-a-proposal, a similar operation could be written like this:

=C2=A0 =C2=A0 tuple<int, string, string,<= /span> double> tpl { -1, "abc&qu= ot;, "xyz", .5 };
=C2=A0 =C2=A0 tuple<int, string> tpl1;
=C2=A0 =C2=A0 tuple<string, double> tpl2;

=C2=A0 =C2=A0 std::tie(tpl1~..., tpl2~...) =3D tpl;

=C2=A0 =C2=A0 assert(std::= get<0>(tpl1) =3D=3D std::get&= lt;0>(tpl));
=C2=A0 =C2=A0 assert(std::get<1&g= t;(tpl1) =3D=3D std::get<1>(t= pl));
=C2=A0 =C2= =A0 assert= (std::get<0>(tpl2) = =3D=3D std::get<2>(tpl));
=C2=A0 =C2=A0 assert(std::get<1>(tpl2) =3D=3D std= ::get<3>(tpl));
<= br>
In general, I think that the C++ standard library is wo= efully lacking in tuple manipulators... but rather than proposing new tuple= manipulators (of which there could be a million: zip, fold, map, car, cdr,= reverse,...), we should be trying to give people the ability to express th= ose manipulators natively in the language, via something like Matthew's= [:] notation or my ~... notation.

my $.02,
<= div>=E2=80=93Arthur

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