220 41171 article Path: news.gmane.org!.POSTED!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Function Parameter of Struct Type -> Named Parameters Date: Fri, 30 Nov 2018 14:56:50 -0500 Lines: 63 Approved: news@gmane.org Message-ID: References: <20181129060523.GA21632@noemi.bahnhof.se> <20181130020338.GA2787@noemi.bahnhof.se> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1543607688 4584 195.159.176.226 (30 Nov 2018 19:54:48 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 30 Nov 2018 19:54:48 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 To: Hyman Rosen , std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBBNMQ3QAKGQEDSE7HHY@isocpp.org Fri Nov 30 20:54:44 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt1-f199.google.com ([209.85.160.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gSos7-000146-V6 for gclcip-std-proposals@m.gmane.org; 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[66.194.253.20]) by smtp.googlemail.com with ESMTPSA id f201sm2756454qke.0.2018.11.30.11.56.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 30 Nov 2018 11:56:51 -0800 (PST) Openpgp: preference=signencrypt In-Reply-To: Content-Language: en-US X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="XMv/DP5D"; spf=pass (google.com: domain of mwoehlke.floss@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=mwoehlke.floss@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE 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:41171 Archived-At: On 30/11/2018 14.10, Hyman Rosen wrote: > On Fri, Nov 30, 2018 at 2:01 PM Matthew Woehlke wrote: >> On 30/11/2018 11.05, Hyman Rosen wrote: >>> Named arguments (in my preferred and correct Ada style) are handled by >>> the compiler without any ABI or mangling changes needed. You cannot >>> overload based only on different parameter names. >> >> Let's say you have this feature implemented in such manner. How do you >> make this (not) work: >> >> int foo(int: a, int: b); >> std::invoke(foo, .a=5, .c=12); // should be an error > > In my version of named argument association, the std::invoke function > would need to have at least three parameters, two of which are named > a and b. The std::invoke call is not a function call of foo, so the > parameter names of foo are irrelevant. Riiiight... So, what you're saying, is forwarding named arguments doesn't work. That's a shame. It's also a feature that some people (myself included) want. Forwarding named arguments Just Works when names are part of the type (e.g. P1229). > I'm not sure what you're getting at here. Really? std::invoke (and I mean *std::invoke*; I didn't chose that by accident) transparently forwards its arguments to some other function, also given in the call site. On its own, it takes whatever arguments you give it, and just passes them along. Therefore, it seems "obvious" that I should a) be able to pass named arguments to std::invoke, and b) that std::invoke should call the function passed to it using those named arguments. That is: int foo(int: a, int: b); std::invoke(foo, .a=5, .c=12); ....should result in a compile error, because I am trying to call `foo` with non-matching arguments. More particularly, the above should have the exact same effect as: foo(.a=5, .c=12); ....which I believe pretty much all of us agree should be a compile error. I should be able to do something similar with std::apply. More generally, if I write something like: auto t = std::make_tuple(12, .x=7); ....then `t` should continue to "know" that its second element isn't just an `int`, but one with the 'name' "x". -- Matthew -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/b18e4777-8139-2fcb-df71-cb9a560e7472%40gmail.com. .