220 10602 <536E072F.4060101@wanadoo.fr> article Path: news.gmane.org!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: overloading on function template parameters that don't appear as function parameters Date: Sat, 10 May 2014 13:02:07 +0200 Lines: 110 Approved: news@gmane.org Message-ID: <536E072F.4060101@wanadoo.fr> References: <536CDAF5.4020407@wanadoo.fr> <5978C7F2-F9AF-4B48-B4DF-B3273299F550@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1399719740 13159 80.91.229.3 (10 May 2014 11:02:20 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 10 May 2014 11:02:20 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBMEOXCNQKGQEVN4WIII@isocpp.org Sat May 10 13:02:13 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f197.google.com ([209.85.217.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Wj52g-0000o3-9R for gclcip-std-proposals@m.gmane.org; Sat, 10 May 2014 13:02:10 +0200 Original-Received: by mail-lb0-f197.google.com with SMTP id w7sf2976292lbi.8 for ; Sat, 10 May 2014 04:02:09 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :subject:references:in-reply-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=sK/hH7ARmnZwokTJpRjzV1GESpR7LGuKkQqZvtgEHa8=; b=EuU2mrrdjzCGw6X1Yr4aNg8I4MObSyt7Qu4yd2l/ZHNG2kEIYKhZPXCzZS13SICQQh eMtpLkIlyXRtbk4T+eLA7YhJq5rKIMB0bixoV8swhzJmr2FkumzpvGOigu9PXveovvGY EezhENvoRjuS86A64O8hT0p5qhYaWdh/RgqLozPsK2zB54qGGojIYbAmrO0wswqL0MW9 kS6VVMK558a9LoqetVio/9kxTUsKuw0jF/Jw/+1Hso5QdIOdQ1w8PjTiKGpvOCGxBRBt 3VO+pLov4IKRJWJOw2YWkBja7RdddNq+LKV34gWohZq8crLSIWUpZsh4QV53wRUQOHJG uVE X-Gm-Message-State: ALoCoQlyBQI0ouwt7fnvZrHAVcH1ukhWh+xfgl2JGxMvD2LEdFxIJXFLlaNQAEx1c2eSQJYhr3lz X-Received: by 10.180.93.74 with SMTP id cs10mr878362wib.6.1399719729759; Sat, 10 May 2014 04:02:09 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.90.241 with SMTP id bz17ls255139wib.33.gmail; Sat, 10 May 2014 04:02:08 -0700 (PDT) X-Received: by 10.180.212.107 with SMTP id nj11mr7447866wic.40.1399719728637; Sat, 10 May 2014 04:02:08 -0700 (PDT) Original-Received: from smtp.smtpout.orange.fr (smtp04.smtpout.orange.fr. [80.12.242.126]) by mx.google.com with ESMTP id ku2si2545809wjb.102.2014.05.10.04.02.08 for ; Sat, 10 May 2014 04:02:08 -0700 (PDT) Received-SPF: none (google.com: vicente.botet@wanadoo.fr does not designate permitted sender hosts) client-ip=80.12.242.126; Original-Received: from new-host.home ([2.11.192.45]) by mwinf5d59 with ME id 0B271o00e0zDXEA03B27sK; Sat, 10 May 2014 13:02:08 +0200 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Sat, 10 May 2014 13:02:08 +0200 X-ME-IP: 2.11.192.45 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 In-Reply-To: <5978C7F2-F9AF-4B48-B4DF-B3273299F550@gmail.com> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: vicente.botet@wanadoo.fr does not designate permitted sender hosts) smtp.mail=vicente.botet@wanadoo.fr 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:10602 Archived-At: Le 10/05/14 09:46, Nicola Gigante a =E9crit : > Il giorno 09/mag/2014, alle ore 15:41, "Vicente J. Botet Escriba" ha scritto: >> Hi, >> >> this is not a proposal yet, but I have preferred to post it here as it i= s related to a proposal I'm working on. >> >> I would like to overload a make_error function >> >> template >> ER make_error(E e); >> >> Note that ER doesn't appear as function parameter. >> >> that can be used as >> >> auto err =3D make_error(std::string("hhhh")); >> >> The following doesn't works as there are ambiguity between the generic o= verload (1) and the specific one (2). >> >> namespace std { >> template >> ER make_error(E e) // (1) >> { >> return ER(e); >> } >> template > , typename std::enable_if::value,= int>::type =3D 0 >> std::exception_ptr make_error(E e) // (2) >> { >> return std::make_exception_ptr(e); >> } >> >> } >> namespace boost { >> template ::value, int>::type =3D 0 >> none_t make_error(E) >> { >> return none; >> } >> } >> >> I have reached to make it work adding an indirection as follows >> >> namespace std { >> template >> ER make_error(E e, ER*) >> { >> return ER(e); >> } >> >> template >> ER make_error(E e) >> { >> ER* ptr=3D0; >> return make_error(e, ptr); >> } >> >> template >> std::exception_ptr make_error(E e, std::exception_ptr*) >> { >> return std::make_exception_ptr(e); >> } >> } >> namespace boost { >> template >> none_t make_error(E, none_t*) >> { >> return none; >> } >> } >> >> >> Is this the correct way to define this generic interface? >> Do you see any failures I have not identified in the design? >> Do you know of a better way to manage with this kind of factory function= s? >> > I don't think you need new language features here. I'd delegate the creat= ion of the error object to a function in a trait class with different speci= alizations so you have a single factory function. In this way you also obta= in the flexibility for the user to customize the behavior for their error t= ypes in the same way you do for exception_ptr. > I'm not requesting a new language feature. My intention is of course that this function could be "specialized" by=20 the user (See the "specialization" for moons::none_t. I've considered=20 the trait already and currently expected uses it already. In fact=20 the design of the post is just an alternative based more on a Concept=20 than on a Trait. Vicente --=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/. .