220 26561 <4ac3803f-a87d-4551-947f-43f106bdda20@isocpp.org> article Path: news.gmane.org!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: auto type deduction for *_cast return argument Date: Tue, 5 Jul 2016 08:07:31 -0700 (PDT) Lines: 80 Approved: news@gmane.org Message-ID: <4ac3803f-a87d-4551-947f-43f106bdda20@isocpp.org> References: <58140e46-2adc-4eac-8f51-72d3685cdf0b@isocpp.org> <7E3409C2-A2AC-4562-BB06-6D5D5ACE8AC8@gmail.com> <00caca39-d36a-475c-840f-79759e99265d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_367_161175421.1467731251596" X-Trace: ger.gmane.org 1467731257 2562 80.91.229.3 (5 Jul 2016 15:07:37 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 5 Jul 2016 15:07:37 +0000 (UTC) Cc: xavinaar@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBNE2565QKGQEAIIIA6A@isocpp.org Tue Jul 05 17:07:35 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f197.google.com ([209.85.214.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bKRwk-0002Rt-J7 for gclcip-std-proposals@m.gmane.org; Tue, 05 Jul 2016 17:07:34 +0200 Original-Received: by mail-ob0-f197.google.com with SMTP id da8sf213092740obb.1 for ; Tue, 05 Jul 2016 08:07:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=rWbXZjhrlQhNyxX8qVB41klwYnMtwNTpqVqTwOetRNs=; b=UozrCyzFC8kMdlCr9oyax0jD9Z21GqjCBf2VdtGTuxms6XbN4GvoxSq33iLJ3L+1uC 0wukAPx5FHABZHU4NtBcofwZDlCeSrLFCzg66T3MQTwCqt86PqUse3lB1+yyFHmIt09w BltZQIiotpiloGdBUb5UjVEB7JVL0lIcaudQmzG9mgnHlYOxWjzixH6eO4EVI1WCJfwH fP+4D1q+ND8II8y4sGhZlNoPn+Kv624joWcK4vFei7NhhdG/2qJMJUSg5IiRp7oZwYzm x4D42dhz/IcMLFaK9f9XgaqLDv7L4S6V5+Fxc3hwQYi17o3idKiYNP7KatF4AE8uwysM yCqw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=rWbXZjhrlQhNyxX8qVB41klwYnMtwNTpqVqTwOetRNs=; b=ae/TPzdeijYpUvwp7UEsWqwhuUkurBl92w2I4h6qZYlOnO3RxqA2IK09EimnCHkMKB fWEKwXOnwJj/kvSebMbk+6nNv4bf0x+isfq2OSYZnfVMzcsHAnQIU36L3xybXVGNFv9V q+yJ9ylMBGVisrdrpCCPyTmkE/fOHPaRFUJ37u94DuN7aAjQV7LjvbaERiz9teRn3aJ0 iA8MWM4dYdl56l0FVkdBWrzdzJ6euzr6Dl1crC9So7JQYSSEww2530AZuau21rsfHqXg 4BwkLyIttqwRGZxOrL9VhibO75JaS/xeBHSkxDOUNrDwitzFp4BEfIiMYo4HqdeuZMGX ZTVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=rWbXZjhrlQhNyxX8qVB41klwYnMtwNTpqVqTwOetRNs=; b=RJmhFC3m+niVVFexfLywcwaDmo/Ha4p4HfSBw1n2q++1VAMCdd0QGkQ09RJ51FX9fA skW0TiCOrqi/3utQ0rfH4MbFlu0NWhrpXWmmE4nhiuTqMsZn0qBOpHPIJ8/10EhHJz+g 6MfLyn9a75FH1LI6zMemUlsWw66n97dHGQTXvkC4pkPrT4taKaAfHrDJlzUjS5yKHyW7 J7hlEZeaeq4jhYyI8bFcFnLxfDudzKHq0o2WMnvpkAsmk1zWzn5vqAi3jbNYL4F71Mdr KWRT4sCpsybS+/Yy7TrHDS8IScHF8Z0SwhzmbRmSvjYZIKv4px7SRAQfyQUh9cnUeu3q /+iA== X-Gm-Message-State: ALyK8tJIex18cE/QE+YZihz36+usHBvN9yhSp3KLcuDilAcnSgk7sSO9eMAckVE3Aqs/Zw== X-Received: by 10.36.146.5 with SMTP id l5mr17703879itd.0.1467731253530; Tue, 05 Jul 2016 08:07:33 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.133.31 with SMTP id h31ls1930789iod.38.gmail; Tue, 05 Jul 2016 08:07:32 -0700 (PDT) X-Received: by 10.36.17.15 with SMTP id 15mr429070itf.10.1467731252494; Tue, 05 Jul 2016 08:07:32 -0700 (PDT) In-Reply-To: <00caca39-d36a-475c-840f-79759e99265d@isocpp.org> X-Original-Sender: jmckesson@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:26561 Archived-At: ------=_Part_367_161175421.1467731251596 Content-Type: multipart/alternative; boundary="----=_Part_368_848721670.1467731251596" ------=_Part_368_848721670.1467731251596 Content-Type: text/plain; charset=UTF-8 On Tuesday, July 5, 2016 at 4:18:44 AM UTC-4, xavi...@gmail.com wrote: > > On countrary: passing *dynamic_cast* to function always means you want to > cast to function argument type. > *Which* function's argument type? By foisting deduction on the function, you basically make overloading impossible for that particular argument. Additionally, you've forgotten something very important about `dynamic_cast`: *it can fail*. If `f` takes a pointer, does it expect to get a nullptr for that parameter? If `f` takes a reference, does the code calling `f` expect to get a `std::bad_cast` exception? Will throwing such an exception break other expressions being evaluated to call `f`? Indeed, this is a good reason to *not* make such casts easier to type. If you're using casts so frequently that you need a language change to avoid lots of repetition, then I'd say that your code is doing something wrong. Explicit casting should be sufficiently exceptional in your codebase that if it takes a few extra keystrokes, you can live with it. -- 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/4ac3803f-a87d-4551-947f-43f106bdda20%40isocpp.org. ------=_Part_368_848721670.1467731251596 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tuesday, July 5, 2016 at 4:18:44 AM UTC-4, xavi...@gmai= l.com wrote:
O= n countrary: passing dynamic_cast to function always means you want = to cast to function argument type.

Which<= /i> function's argument type? By foisting deduction on the function, yo= u basically make overloading impossible for that particular argument.
Additionally, you've forgotten something very important about `dynami= c_cast`: it can fail.

If `f` takes a pointer, does it expect = to get a nullptr for that parameter? If `f` takes a reference, does the cod= e calling `f` expect to get a `std::bad_cast` exception? Will throwing such= an exception break other expressions being evaluated to call `f`?

I= ndeed, this is a good reason to not make such casts easier to type. = If you're using casts so frequently that you need a language change to = avoid lots of repetition, then I'd say that your code is doing somethin= g wrong.

Explicit casting should be sufficiently exceptional in your= codebase that if it takes a few extra keystrokes, you can live with it.

--
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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/4ac3803f-a87d-4551-947f-43f106bdda20= %40isocpp.org.
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