220 29336 <2128372.NTAZafObDQ@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: std::byte thoughts Date: Tue, 01 Nov 2016 23:43:31 -0700 Lines: 89 Approved: news@gmane.org Message-ID: <2128372.NTAZafObDQ@tjmaciei-mobl1> References: <7da80620-e4bd-40eb-a4ec-4f3c2dcb2c98@isocpp.org> <2350841.Z7lUCKSumT@tjmaciei-mobl1> <3e64b220-79ae-4108-ba1c-9785494fc434@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1478069032 28828 195.159.176.226 (2 Nov 2016 06:43:52 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 Nov 2016 06:43:52 +0000 (UTC) User-Agent: KMail/5.3.2 (Linux/4.8.4-1-default; KDE/5.27.0; x86_64; ; ) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBFUW43AAKGQEBGPPTDI@isocpp.org Wed Nov 02 07:43:48 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f70.google.com ([74.125.82.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c1pGm-0004zG-B3 for gclcip-std-proposals@m.gmane.org; Wed, 02 Nov 2016 07:43:32 +0100 Original-Received: by mail-wm0-f70.google.com with SMTP id 79sf3505165wmy.6 for ; Tue, 01 Nov 2016 23:43:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=from:to:subject:date:message-id:user-agent:in-reply-to:references :mime-version:content-transfer-encoding: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=BrghJjlrwkTJW2ba28b1bwoMuN/WF/sjBrxqDrYZHOw=; b=frNphZQYOPH0hMm+/SAzaowAF2xuF5UjY9JEI8/O+bmDW/fR8Re4jp7rBNdxHhqczE xe4plEhV5Pg1J+/bbIVe8ZG+/sjIqks77AVy1kXpHG06lcZ9fcWXoYY7YN4iTVdsoN3o B/R9Rs9PZKJ054vNdrtqhUHLwurR02VqpydrIo8VJyyv24qgHQWl8o5VLzREQwgIpox9 8qUPsgZzpiIo1jh9+c7yLaWpbYbu4ZKT/7H8fNpe85YN4QtilabeAEv0Wx6e8gYxr4V7 hGe58lPNZ9VW4AfojvrCTkqjTnsZZeyVuH0/OhZW0xeLbpFzaglpaQJPXbkh5/4QLWDO X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:subject:date:message-id:user-agent :in-reply-to:references:mime-version:content-transfer-encoding :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=BrghJjlrwkTJW2ba28b1bwoMuN/WF/sjBrxqDrYZHOw=; b=YzABc282jRp62xMX/ID/zOqMIAHjoqC0gK7ZuCeJi7cDNDekXFcQIQWLIzQQoBdgOM xJFsWHu3lq21dCL4m5dR6UUSJv2fQeb6Ngqq6p1bbfLo7MWiy14JuLtRmFp6XcrRBxoH VHqv7olZ0w7mfCXmjVcswxPbmVRHYoy7XQMAsLDgIfkq9abSDxXi2Xmm7uTXXeJOn9v3 iPPGWv7R9DhwpxnjzxpK30EpFiGiEAZ7CNCo9vCw/F/MT8hrQC0PRUQr8nGogEdtnNC8 /bl0rTmdfTtrlnNqeQKLGV45T9Oy/3D7ZpJfv9tXEoW323InEqIsM4CMvrl25TZsqgtb X-Gm-Message-State: ABUngvff2Iu6u3C04daO7hBYkitUAqmV4sG+OK4fXLcIrJErVbke9nIchutbLGlZKxLKhg== X-Received: by 10.28.156.13 with SMTP id f13mr6541wme.10.1478069015344; Tue, 01 Nov 2016 23:43:35 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.193.15 with SMTP id r15ls196591wmf.20.gmail; Tue, 01 Nov 2016 23:43:34 -0700 (PDT) X-Received: by 10.28.4.4 with SMTP id 4mr1185039wme.23.1478069014125; Tue, 01 Nov 2016 23:43:34 -0700 (PDT) Original-Received: from gondolin.macieira.info (gondolin.macieira.info. [78.47.120.188]) by mx.google.com with ESMTP id 203si1440853wmm.118.2016.11.01.23.43.34 for ; Tue, 01 Nov 2016 23:43:34 -0700 (PDT) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) client-ip=78.47.120.188; Original-Received: from tjmaciei-mobl1.localnet (unknown [IPv6:2601:1c0:4501:5f9f:d130:7f7c:ebed:53ad]) by gondolin.macieira.info (Postfix) with ESMTPSA id 8D06A11B3B5 for ; Tue, 1 Nov 2016 23:43:33 -0700 (PDT) In-Reply-To: <3e64b220-79ae-4108-ba1c-9785494fc434@isocpp.org> X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) smtp.mailfrom=thiago@macieira.org Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: 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:29336 Archived-At: Em ter=C3=A7a-feira, 1 de novembro de 2016, =C3=A0s 22:16:32 PDT, Nicol Bol= as escreveu: > On Wednesday, November 2, 2016 at 12:55:46 AM UTC-4, Thiago Macieira wrot= e: > > That would also not be a good idea because, unsigned char is, by > > defintion, a > > byte. Why should we have (more) types that mean exactly the same thing, > > and > > this time in all platforms, by definition? >=20 > Because "unsigned char" *also* means "unsigned character". With just > `unsigned char`, there is no way to distinguish between manipulating byte= s > and manipulating unsigned characters. >=20 > That's what `byte` is for, as a type: a way to semantically differentiate > between operations on bytes and operations on characters. The types can b= e > inter-convertible, numerically speaking, but they don't mean the same thi= ng. I'm sorry, I don't agree that there's a distinction in the first place. Byt= es=20 are used more often than just copying around. If you add, subtract, shift l= eft=20 or right, perform bitwise operations, etc, you need the value. If I need th= e=20 value, then a zero is a zero is a zero, a 0x40 is still a 0x40. Also, I can assign 'a' to any integer type. Maybe this was the main issue:= =20 that single-quote character literals automatically convert to integral,=20 instead of staying a character. We're 40 years too late to change this, tho= ugh=20 (since B). > My problem with using C++ enum chicanery is that, if you use the type > traits mechanisms to ask what `std::byte` is, it will say that it's an > enum, not that it's an integral type. There's no reason why `byte` should > not be an integral type. Agreed, but I'm going to go further and say that it's pretty useless for a = lot=20 of use-cases. I need a value of a lot of operations and an enum won't give = it=20 to me unless I cast it to a suitable integral in the first place -- unsigne= d=20 char (that is, a *real* byte). This week I've been spending time working on hashing algorithms, notably=20 SipHash (btw, implementations should reconsider their std::hash algorithms)= ..=20 In order to implement it, I needed to access the byte array and do byte-lev= el=20 operations like rotating left, XOR, and additions. Not only would std::byte= =20 not work for me, I fail to see how the operations I'm doing are any differe= nt=20 than the operations on an unsigned char. > It's the same reason why we have `char16_t` as a distinct type from > `uint_least16_t`. Because there is a fundamental semantic difference > between an array of unsigned integers that are at least 16-bits in size a= nd > an array of UTF-16 code units. One of this is a string; the other is not. The only benefit I see there is allowing overloading. But while that may be true, what's the point of an *unsigned* char? If you= =20 want to do character operations, you use char. If you're using unsigned cha= r,=20 that's because you want a byte, plain and simple. By this argument, we alre= ady=20 have the distinction between character operations and byte operations. --=20 Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center --=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/2128372.NTAZafObDQ%40tjmaciei-mobl1. .