220 13609 article Path: news.gmane.org!not-for-mail From: Nicola Gigante Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: The view concept Date: Fri, 3 Oct 2014 08:56:42 +0200 Lines: 99 Approved: news@gmane.org Message-ID: References: <428c47bd-67f2-47d1-98c0-e5ca85698076@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1412319414 19008 80.91.229.3 (3 Oct 2014 06:56:54 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 3 Oct 2014 06:56:54 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDMMZOF5V4KBBLMRXGQQKGQEIJJNZCA@isocpp.org Fri Oct 03 08:56:47 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f199.google.com ([209.85.212.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XZwnH-0004kE-54 for gclcip-std-proposals@m.gmane.org; Fri, 03 Oct 2014 08:56:47 +0200 Original-Received: by mail-wi0-f199.google.com with SMTP id d1sf434020wiv.6 for ; Thu, 02 Oct 2014 23:56:46 -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:subject:from:in-reply-to:date :message-id:references:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type:content-transfer-encoding; bh=fl9YunSoecE4jZX9v06mRYbJCpatBmpzJxW5quCaWvo=; b=UkYdEeggLeUyEVJiYwPC7IEIR9NU1MxGAQIVrgUmcO/YIFFAjtlVHIWN3w2qjUBekA LD7fqARq3RAcTBjzNKuu5Q7nnQvVV+cK9ePtaRxYcRArkQEpKXinrTojKgczPsxuaqo5 B9p3RB8wFnqrFqV+emhTanJxKONq3J9VPjPQro2WFq1+rt0miveC860tA/cCkPrmZUTA QiUSzMBP68f9up9FACW28SdDcZvQHj2dDl5Ggd5zr72CZtnIm+qdXjUx0y3s01Kd60GD 6NpVES9K/V/NsQHwDOMra8ytnJHrSuC5bT3QQC3o97+XfUuEiwfolQIFXhjX0AigPJxN rD6Q== X-Gm-Message-State: ALoCoQmhGy2NxhYWu+MHVZQ93wlLbBDy9+mdhod/v/hSU6y6smnNjvK21MMpXhPoX2phf4YZMmPg X-Received: by 10.152.29.130 with SMTP id k2mr646738lah.3.1412319406806; Thu, 02 Oct 2014 23:56:46 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.103.8 with SMTP id fs8ls193942wib.48.canary; Thu, 02 Oct 2014 23:56:45 -0700 (PDT) X-Received: by 10.180.86.73 with SMTP id n9mr10004792wiz.30.1412319405557; Thu, 02 Oct 2014 23:56:45 -0700 (PDT) Original-Received: from mail-wi0-x235.google.com (mail-wi0-x235.google.com [2a00:1450:400c:c05::235]) by mx.google.com with ESMTPS id em19si7898631wjd.52.2014.10.02.23.56.45 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 02 Oct 2014 23:56:45 -0700 (PDT) Received-SPF: pass (google.com: domain of nicola.gigante@gmail.com designates 2a00:1450:400c:c05::235 as permitted sender) client-ip=2a00:1450:400c:c05::235; Original-Received: by mail-wi0-f181.google.com with SMTP id hi2so1125564wib.14 for ; Thu, 02 Oct 2014 23:56:45 -0700 (PDT) X-Received: by 10.180.75.49 with SMTP id z17mr9941535wiv.3.1412319405458; Thu, 02 Oct 2014 23:56:45 -0700 (PDT) Original-Received: from [158.110.153.153] ([158.110.153.153]) by mx.google.com with ESMTPSA id iy10sm1081664wic.5.2014.10.02.23.56.43 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 02 Oct 2014 23:56:44 -0700 (PDT) In-Reply-To: <428c47bd-67f2-47d1-98c0-e5ca85698076@isocpp.org> X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: nicola.gigante@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of nicola.gigante@gmail.com designates 2a00:1450:400c:c05::235 as permitted sender) smtp.mail=nicola.gigante@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-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:13609 Archived-At: Il giorno 03/ott/2014, alle ore 07:40, Matthew Fioravante ha scritto: > With array_view, string_view, and now possibly bitset_view, this view thi= ng is becoming contagious. >=20 > I think at this stage it makes sense to precisely define exactly what a v= iew is and how it behaves as a concept. Any kind of view type that is inven= ted now or in the future should adhere to a set of rules so that they all h= ave a uniform interface. >=20 > First, what exactly is a view? >=20 > I would define it as an adapter over a fixed size contiguous range of mem= ory. >=20 I like the idea to set in stone those definitions.=20 First question, why is the memory block necessary contiguous for all kinds of view? I think it would be reasonable to expect a bitset_view to work on top of a strided array_view that sits on top of a contiguous buffer. You could even have things like a filter_view, that discards elements that don't satisfy a predicate, on top of a sorted_view, etc... If one goes this way I see some overlap with the work in progress on ranges. Maybe the two things could be made to fit together (a view will be a range, anyway). The contiguity is necessary to support the data() member, but other than that it is sufficient that the underlying container/buffer have random access iterators, I think. If it only has forward iterators you can remove the operator[] from the interface through SFINAE=20 and only provide iterators yourself. > How does a view behave with respect to common operations? >=20 > Let's compare a view, to a T, and T* and see how they behave. These ru= les are derived from string_view and array_view. >=20 > T =3D T: copy the value (deep copy) > T* =3D T*: reassign the pointer (shallow copy) > view =3D view: reassign the view (shallow copy) >=20 > T =3D=3D T: compare 2 values (deep compare) > T* =3D=3D T*: compare whether 2 pointers point to the same thing (shallow= compare) > view =3D=3D view: compare the values (deep compare) >=20 > T.foo(): direct member invocation of T > (T*)->foo(): indirect member invocation of T > view.foo(): direct member invocation of the view type methods >=20 > Questions: > 1) How do we shallow compare 2 views? > 2) How do we deep copy a view? >=20 > What are the common operations for any view? >=20 > 1) We can iterate over a view with begin()/end() > 2) We can access an element using operator[] / at() / front() / back() / = data() > 3) We can ask for the size() and whether or not the view is empty() > 4) We can shrink the view by removing front or back elements, but not mak= e it larger. Once you chop off the front or back of the view, you can never= recover it. > 5) We can reassign the view to another source array > 6) We can compare 2 views >=20 > The array_view proposal also gets into multi-dimensional views and stridi= ng, but I'm not going to go there yet. >=20 > If there are a certain set of operations that apply to any kind of view, = then perhaps it makes sense to define and mandate them for all of the view = classes. This could even be done with inheritance. Have a basic_view bas= e class which implements the above methods and have array_view (striding / = sectioning / dimensions), string_view (string class), bitset_view (bit mani= pulation) build on top of that. >=20 Good ideas! Bye, Nicola --=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 http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. .