220 23646 <56914870.3020407@wanadoo.fr> article Path: news.gmane.org!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: invoke and unpacking tuple-like type instances Date: Sat, 9 Jan 2016 18:50:40 +0100 Lines: 111 Approved: news@gmane.org Message-ID: <56914870.3020407@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed X-Trace: ger.gmane.org 1452361851 10674 80.91.229.3 (9 Jan 2016 17:50:51 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 9 Jan 2016 17:50:51 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBDH67CONY4PBB4UQYW2AKGQE3GZ4DKA@isocpp.org Sat Jan 09 18:50:44 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aHxf2-0001oN-0C for gclcip-std-proposals@m.gmane.org; Sat, 09 Jan 2016 18:50:44 +0100 Original-Received: by mail-lf0-f70.google.com with SMTP id k69sf15270572lfg.3 for ; Sat, 09 Jan 2016 09:50:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=from:subject:to:message-id:date:user-agent:mime-version :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=0MEdUYeAbAGurTeQk6A1SInec7F0Pt+MVPqlrLF4lHM=; b=wTgM48cEHclsjMeDxwVZ95FSiMLsqzlk0DzeTUHru5hijO7R/mrAk5RPNAdtr7+Ilt r4jH/SSl/AYFEWpN9bHpIcRT0ifD1a7ZsSX5W3WchMzieNgdlOyYdDhuxuXYoUtFzqQI wxrcrcoFxYT2ofFMXGQTyEYq0knINTwwT9T1nmIhCFJFMm8eCfMiHbPI6o7TxITaN+fy i4qJef2P/YMuZGxrgXcQIJc/V1CugXO8DLr9G37CAn6ik9qqJDvcbkwQ9BDKerJT1i/S Giu1ZhJlRPhwaVaWQLX8Zs24yOlcEvjjYICAc9Cf0kFOaFlQgjZoZgCB8FrKTdQ3EWKM gr+Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:subject:to:message-id:date:user-agent :mime-version: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=0MEdUYeAbAGurTeQk6A1SInec7F0Pt+MVPqlrLF4lHM=; b=LQIADqr3vEpEToqhE+ZZjGIA4p2SELfvkgyaVfVCRRHvBWE/PWUZ7ahDYjT7/00NKd BeLhc0pUJGgcFixaR61v0LWrCEbDjH0qJPHKKoaKIzhg8wXyHXDXa+7uFrq5ZN4zrRgi hCFgrN+Xxik3Mt62P9soltXQnW9Ku6hDxGmviI6zCQ8oJSZnZK91DFf+D4OIww3GPp6T F/fJ1mvQhgkEiRO+ncqnU4tVOKLpCfPtLQID+ocP51jClBohJWt3npde6WLJNmhBNwgp IKGCrmctuGUugh3l+xLtgHQxvY2rnjJ/PygoOeCgVfuB98UXp64cnpCsBeP7p9+Sys58 dS2A== X-Gm-Message-State: ALoCoQlUq6mkvEgRGp+7UvX43AYMywpnDh9aGrrAda+C+0QD/CCvI3Wa1dc1UbV8pLsGN8gSiFk+qUieiKH/fGXbUzClQRmvVQ== X-Received: by 10.28.127.206 with SMTP id a197mr774432wmd.6.1452361843321; Sat, 09 Jan 2016 09:50:43 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.47.13 with SMTP id v13ls151449wmv.36.gmail; Sat, 09 Jan 2016 09:50:41 -0800 (PST) X-Received: by 10.28.17.8 with SMTP id 8mr4589930wmr.65.1452361841841; Sat, 09 Jan 2016 09:50:41 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp07.smtpout.orange.fr. [80.12.242.129]) by mx.google.com with ESMTPS id v10si184074140wjx.223.2016.01.09.09.50.41 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sat, 09 Jan 2016 09:50:41 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.129 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.129; Original-Received: from new-host.home ([86.214.79.135]) by mwinf5d13 with ME id 3tqg1s00Q2v9yza03tqgvc; Sat, 09 Jan 2016 18:50:41 +0100 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Sat, 09 Jan 2016 18:50:41 +0100 X-ME-IP: 86.214.79.135 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.129 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:23646 Archived-At: Hi, I would like to have some feedback on a function that acts as unpacking tuple-like classes in the context of the invoke function. This was presented already with the name args(t) as an alternative library solution to unpack tuple in the thread "[std-discussion] Distinction between Argument packs and tuples" [1] where an operator... on tuple was proposed. The proposed operator... introduced breaking changes and so another operator would be needed. make_tuple packs some elements in a tuple. It seem natural to think of unpacking a tuple into its elements, so that make_tuple(unpack(t)) == t // that is (pack . unpack = id) The same applies to forward_as_tuple: forward_as_tuple(unpack(g())) == g() The result of unpack could be a wrapper unpacked as ref wraps a reference in a reference wrapper. Having this, we can adapt invoke so that, if some of its args are unpacked, invoke would work as if invoke(f, a, b, unpack(t1), d, unpack(t2)) = apply(f, tuple_cat(forward_as_tuple(a), forward_as_tuple(b), forward_as_tuple(unpack(t1)), forward_as_tuple(d), forward_as_tuple(unpack(t2)))) apply(f, tuple_cat(forward_as_tuple(a), forward_as_tuple(b), t1, forward_as_tuple(d), t2)) apply(f, tuple{a, b, get<0>(t1), ..., get(t1), d, get<0>(t2), ...., get(t2})); invoke(f, a, b, get<0>(t1), ..., get(t1), d, get<0>(t2), ..., get(t2)); f(a, b, get<0>(t1), ..., get(t1), d, get<0>(t2), ..., get(t2)); where Ni is the tuple_size::value Definition when one of Args is unpacked template auto invoke(F&& f, Args args...) { return apply(forward(f), forward_as_tuple(forward(args)...); } unpack shoudl works with lvalue and rvalues template unpacked> unpack(TL & tl); template unpacked> unpack(TL && tl); and unpack on unpacked doesn't changes anything as ref with reference_wrapper template unpacked& unpack(unpacked & tl); template unpacked const& unpack(unpacked const& tl); template unpacked && unpack(unpacked && tl); In addition, given a tuple t, what could be the meaning of *t? Well t is not a pointer, but it contains things as optional does, so we can define tuple::operator*() as if we unpacked it std::tuple t; ... invoke(f, a, b, *t1, d) == f(a, b, get<0>(t1), ..., get(t1), d); Note that if as_const is accepted there is no need for a specific cunpack function as unpack(as_const(t)). Note also that unpack would works not only for std::tuple, but with any tuple-like type providing get access. However the operator* need to be defined explicitly for each tuple-like type :( Bike-shading: unpack/unpacked unpack/tuple_like_wrapper ... Waiting for a language-based proposal, is there an interest in a library proposal providing a partial solution (unpack needs invoke to be expanded)? Best, Vicente P.S. Any [1] https://groups.google.com/a/isocpp.org/forum/#!topic/std-discussion/qsM_4DijZFM -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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