220 21330 article Path: news.gmane.org!not-for-mail From: Shahms King Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: missing hash_code result in P0029 Date: Mon, 05 Oct 2015 22:33:50 +0000 Lines: 176 Approved: news@gmane.org Message-ID: References: <1572715.jJmjmrJA0J@tjmaciei-mobl4> <1894409.GHBCqMxsGN@tjmaciei-mobl4> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a113d9f7a0f81e50521631c8d X-Trace: ger.gmane.org 1444084450 4612 80.91.229.3 (5 Oct 2015 22:34:10 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 5 Oct 2015 22:34:10 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC7ML3M6QIDBBWHVZOYAKGQET3VETEI@isocpp.org Tue Oct 06 00:34:04 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f70.google.com ([209.85.213.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZjEKY-00024p-Pd for gclcip-std-proposals@m.gmane.org; Tue, 06 Oct 2015 00:34:02 +0200 Original-Received: by vkao3 with SMTP id o3sf261402831vka.1 for ; Mon, 05 Oct 2015 15:34:01 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=TsKB7p/o5DiwW0DBJyG8gVjuFEWiIyoNHuIpWqPEALg=; b=feSjDZQ+ZkCjxKoAWRb/7lRIgApmpYWKJDteyayto8q7PDZP1zm34LHoy+SkYpJl6o xI/FUD50QZPguT+KSENj9VszWWhAk35lemyXePIBKSGe54B56TJ6mGx4PqMGuer+TJWZ WEOBBjqU9NLHayGyCGJBhxEGVxxtxJpMMdYTswXXQoDlxVc5x9Lfqf/419lrwIdFehN1 g9u1mhnErRf7TKo2IHIsi/AR4Es5K7fIoYw9RwXSHlrbvTgZOC2Wd1P8dBHRCQWGQzMq zzA0VUuPi3iWh7XI663zUysLadTeCkdtfG0EU5er/XfYgxIADedOYIkOazVx51x7eLgz 35Ug== X-Gm-Message-State: ALoCoQnzOZV9rCe4fzClnwwp7xwp5mMXdTU/Cbv0m8cRfoLx42+9XKkPeogpF1dnwENKb5g/ZN0r X-Received: by 10.31.178.196 with SMTP id b187mr28130381vkf.3.1444084441694; Mon, 05 Oct 2015 15:34:01 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.97.245 with SMTP id m108ls3201312qge.16.gmail; Mon, 05 Oct 2015 15:34:00 -0700 (PDT) X-Received: by 10.31.13.11 with SMTP id 11mr22527709vkn.59.1444084440100; Mon, 05 Oct 2015 15:34:00 -0700 (PDT) Original-Received: from mail-vk0-x232.google.com (mail-vk0-x232.google.com. [2607:f8b0:400c:c05::232]) by mx.google.com with ESMTPS id z22si15462746vkd.175.2015.10.05.15.34.00 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Oct 2015 15:34:00 -0700 (PDT) Received-SPF: pass (google.com: domain of shahms.king@gmail.com designates 2607:f8b0:400c:c05::232 as permitted sender) client-ip=2607:f8b0:400c:c05::232; Original-Received: by vkat63 with SMTP id t63so105956650vka.1 for ; Mon, 05 Oct 2015 15:34:00 -0700 (PDT) X-Received: by 10.31.32.137 with SMTP id g131mr21270056vkg.2.1444084439808; Mon, 05 Oct 2015 15:33:59 -0700 (PDT) In-Reply-To: <1894409.GHBCqMxsGN@tjmaciei-mobl4> X-Original-Sender: shahms.king@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of shahms.king@gmail.com designates 2607:f8b0:400c:c05::232 as permitted sender) smtp.mailfrom=shahms.king@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE 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:21330 Archived-At: --001a113d9f7a0f81e50521631c8d Content-Type: text/plain; charset=UTF-8 As far as I understand it, you don't. std::hash_code is the internal state of whatever hash algorithm is being used by std::hash. Either you're using std::hash, in which case it initializes the std::hash_code through mechanisms unknown and similarly extracts the value or you're using a different algorithm which uses a different type to represent its internal state which conforms to the HashCode concept and you don't traffic in std::hash_code at all. At least, that's my reading of the proposal. Either your hash_value() function accepts std::hash_code and only works with std::hash, or it's a template and supports any conforming hashing algorithm. --Shahms On Mon, Oct 5, 2015 at 1:58 PM Thiago Macieira wrote: > On Monday 05 October 2015 17:34:04 Shahms King wrote: > > You can trivially use them in your own hashing container, as you would > > now. The primary thing that is being changed is the mechanism by which > > user-defined types can supply their data to the hash function, not the > > interface for retrieving final values from that hash function. The > > high-level API for retrieving a hash value from an object is unchanged, > e.g. > > > > template > > struct hash { > > size_t operator() (const T& value) const { > > std::hash_code state = __implementation_defined_init(); > > state = hash_value(state, value); > > return __implementation_defined_extract_value(state); > > } > > }; > > If by __implementation_defined_init(), you mean the way I will initialise > the > hash from my hash seed, I understand. But what constructors and assignment > operators will std::hash_code have so I can create it from my hash seed? > > As for the extract value, I don't get it. > > Can you give as example the two most trivial implementations? That is, the > one > where there's no extra state before or after the hashing of the value type > (no > seed) and the one where the seed is just a global integer value initialised > from a random source. > > -- > Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org > Software Architect - Intel Open Source Technology Center > PGP/GPG: 0x6EF45358; fingerprint: > E067 918B B660 DBD1 105C 966C 33F5 F005 6EF4 5358 > > -- > > --- > 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. > Visit this group at > http://groups.google.com/a/isocpp.org/group/std-proposals/. > -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --001a113d9f7a0f81e50521631c8d Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
As far as I understand it, you don't. =C2=A0std::hash_= code is the internal state of whatever hash algorithm is being used by std:= :hash.=C2=A0 Either you're using std::hash, in which case it initialize= s the std::hash_code through mechanisms unknown and similarly extracts the = value or you're using a different algorithm which uses a different type= to represent its internal state which conforms to the HashCode concept and= you don't traffic in std::hash_code at all.=C2=A0 At least, that's= my reading of the proposal.

Either your hash_value() fu= nction accepts std::hash_code and only works with std::hash, or it's a = template and supports any conforming hashing algorithm.

= --Shahms

O= n Mon, Oct 5, 2015 at 1:58 PM Thiago Macieira <thiago@macieira.org> wrote:
On Monday 05 October 2015 17:34:04 Shahms King wrote:
> You can trivially use them in your own hashing container, as you would=
> now.=C2=A0 The primary thing that is being changed is the mechanism by= which
> user-defined types can supply their data to the hash function, not the=
> interface for retrieving final values from that hash function.=C2=A0 T= he
> high-level API for retrieving a hash value from an object is unchanged= , e.g.
>
> template <typename T>
> struct hash {
>=C2=A0 =C2=A0size_t operator() (const T& value) const {
>=C2=A0 =C2=A0 =C2=A0std::hash_code state =3D __implementation_defined_i= nit();
>=C2=A0 =C2=A0 =C2=A0state =3D hash_value(state, value);
>=C2=A0 =C2=A0 =C2=A0return __implementation_defined_extract_value(state= );
>=C2=A0 =C2=A0}
> };

If by __implementation_defined_init(), you mean the way I will initialise t= he
hash from my hash seed, I understand. But what constructors and assignment<= br> operators will std::hash_code have so I can create it from my hash seed?
As for the extract value, I don't get it.

Can you give as example the two most trivial implementations? That is, the = one
where there's no extra state before or after the hashing of the value t= ype (no
seed) and the one where the seed is just a global integer value initialised=
from a random source.

--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
=C2=A0 =C2=A0Software Architect - Intel Open Source Technology Center
=C2=A0 =C2=A0 =C2=A0 PGP/GPG: 0x6EF45358; fingerprint:
=C2=A0 =C2=A0 =C2=A0 E067 918B B660 DBD1 105C=C2=A0 966C 33F5 F005 6EF4 535= 8

--

---
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-proposals+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
Visit this group at http://groups.google.c= om/a/isocpp.org/group/std-proposals/.

--

---
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.
Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
--001a113d9f7a0f81e50521631c8d-- .