220 39831 <1534441498.3721109.1476442920.71D445BF@webmail.messagingengine.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Henry Miller Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: What do we want from named paramaters Date: Thu, 16 Aug 2018 12:44:58 -0500 Lines: 86 Approved: news@gmane.org Message-ID: <1534441498.3721109.1476442920.71D445BF@webmail.messagingengine.com> 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 1534441375 25593 195.159.176.226 (16 Aug 2018 17:42:55 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 16 Aug 2018 17:42:55 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDQPBM7KRMDBBG7Q23NQKGQEODALRJQ@isocpp.org Thu Aug 16 19:42:51 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f200.google.com ([209.85.216.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fqMIM-0006X3-KQ for gclcip-std-proposals@m.gmane.org; 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[66.111.4.25]) by mx.google.com with ESMTPS id x6-v6si9326552qth.304.2018.08.16.10.44.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 Aug 2018 10:44:59 -0700 (PDT) Received-SPF: pass (google.com: domain of hank@millerfarm.com designates 66.111.4.25 as permitted sender) client-ip=66.111.4.25; Original-Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailout.nyi.internal (Postfix) with ESMTP id 4F03221E44 for ; Thu, 16 Aug 2018 13:44:59 -0400 (EDT) Original-Received: from web2 ([10.202.2.212]) by compute4.internal (MEProxy); Thu, 16 Aug 2018 13:44:59 -0400 X-ME-Proxy: X-ME-Sender: Original-Received: by mailuser.nyi.internal (Postfix, from userid 99) id BB754621BF; Thu, 16 Aug 2018 13:44:58 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface - ajax-7b72137a X-Original-Sender: hank@millerfarm.com X-Original-Authentication-Results: mx.google.com; dkim=temperror (no key for signature) header.i=@millerfarm.com header.s=mesmtp header.b="LS5h/vj1"; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=UF24GRv7; spf=pass (google.com: domain of hank@millerfarm.com designates 66.111.4.25 as permitted sender) smtp.mailfrom=hank@millerfarm.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:39831 Archived-At: In the past couple months I've seen several proposals for names parameters.= Each with a list of pros and cons, and because there are cons arguments a= gainst them. I think we need a discussion on what we want assuming some st= rawman acceptable syntax, and some thought of how many limitations in corne= r cases we are willing to accept.=20 I can think of 4 uses for names parameters. (If you don't understand these = I have simple code examples) 1 . a function with more than one parameter of the same type is called with= the parameters in the wrong order * Some people want this to be a compilation error, some want the com= piler to correct the problem and continue 2. a function wants to take the same type to mean different things in diffe= rent contexts 3. it isn't obvious from the type alone what a parameter means 4. A function has a bunch of defaulted arguments and you want to change one= of the latter ones without specifying all the others First question: is this complete? Second, which problems are worth solving? Third, for problems worth solving, which is the better solution, and how st= rongly attached to it are you? For the first the motivating code is something like: class myMatrix { T GetCell(int row, int column); ... }; in code: cell =3D matrix.GetCell(column, row); This will compile just fine in C++17, but the code is undoubtedly wrong. I= n C++2n do you want this to be a compiler error, or correct code? Second: class point { point(double x, double y);=20 point(double distance, double angle); .... }; This code does not compile in C++17. Do we want to make this case work? Third: class myString { int compare(myString, bool CaseSensitive); .... }; in code if(str.compare(otherString, false) =3D=3D 0) ... // what does this me= an, why would you call compare and not compare? This code is legal C++17, but it is user hostile. False in the context of r= eading the function makes no intuitive sense. Qt has created an enum for t= his, but it can be argued that this is too heavy. (you may or may not agre= e with the argument) Fourth: // warning, marketing regularly changes the default value of this function void foo(double a =3D 1234.5, int b =3D 6789); foo(b:=3D1234); This won't compile in C++17. However it seems like it would be useful to no= t clutter function calls with default parameters that you don't care about.= In the case I gave it is a maintenance problem to update all uses of foo e= very time the defaults change, though I'm not sure if this is actually a co= mmon problem. --=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/1534441498.3721109.1476442920.71D445BF%40webmail= ..messagingengine.com. .