220 29442 <08b6d632-c137-b039-9d79-7e67f9ccecfa@honermann.net> article Path: news.gmane.org!.POSTED!not-for-mail From: Tom Honermann Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allowing string literals to match `char...` packs in templates Date: Thu, 17 Nov 2016 10:33:53 -0500 Lines: 114 Approved: news@gmane.org Message-ID: <08b6d632-c137-b039-9d79-7e67f9ccecfa@honermann.net> References: <9de07b5f-f870-4a02-882f-54f9fdd12ffd@isocpp.org> <6b73bf50-4189-4d5d-a2c0-2debb085659e@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------1ECB6F4A89B94423D6D5BA7C" X-Trace: blaine.gmane.org 1479396837 16904 195.159.176.226 (17 Nov 2016 15:33:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 17 Nov 2016 15:33:57 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDBNXSHG6UDBBYU3W7AQKGQEFZQXQCA@isocpp.org Thu Nov 17 16:33:52 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f197.google.com ([209.85.192.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c7OhE-0003SN-B7 for gclcip-std-proposals@m.gmane.org; Thu, 17 Nov 2016 16:33:52 +0100 Original-Received: by mail-pf0-f197.google.com with SMTP id 17sf115911637pfy.2 for ; Thu, 17 Nov 2016 07:33:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to: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=6RVW5vpCQPga9Vp6OhovgqRNPbJBVhX6aDgLwK5CZxo=; b=jWndHCWrp8nkulE5bQ6LgNlgfPDAO97wrPzEK7VSRAz2fWttts4hf1CTrJW4DQQP3H ohljYy3aYOqLAFirtcrwDbBWgjKR955bwq0Wj0Zedxp8RC6VBT01t8yXax+p/3ZRj41H ddb9ihJ2Q6JyiikuxqoPGhmcyRqYUCYPDG0+Aa2W/valL8resq512jg+m1//bC0BPfy7 vytrkVk15GDai0hxcTZf2g4YBU8avOD0HQQtfQPBjZXAhdxpaVGyu2CDgVASm5OKSP6M vz21Obrb2gwNe6n09d6doQDoeZrrrRC+lyoQKZfEdOnUUAho+bx2eI7iH0gKUEIEhtGW ye5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to: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=6RVW5vpCQPga9Vp6OhovgqRNPbJBVhX6aDgLwK5CZxo=; b=FDOQhXIy3qHP3dR6c5vo1vi8ZRWFG0RB7/1BuyH1qssKu+KZiVSKHDalfwjl7Qaz99 DUcoIO7TuQDonOPYASSLmvYpE2pmQHnawZtMbw5pf6/ckvpAkSNRuoKPkSYU43zh8YIW LNAz0tSY5STnuCOzJKaROoT0au/mMjm59AppJwK+AVoc2Urxn5/7L8lS0x96Rwu0rfJw hQei2y+SGgsOQSzTPO4WAxbX0dF0FCIA7gg0pz46lJLlNNdpKeaU0F40i5pQnmaSnbrd zcfuUoVx7nthwS9cfGtibZ9fZCMG63aLf8z0P1Cr68x2YOPaVZhNaj9aTn264o6MXpaV TVCA== X-Gm-Message-State: ABUngvdVCLHvMVSZZf+irQIn6T5UTRHN7mqidaJFmt8eywZFT7XOiO+c/wkrsz+ECLF7IQ== X-Received: by 10.99.97.214 with SMTP id v205mr1369394pgb.36.1479396835492; Thu, 17 Nov 2016 07:33:55 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.164.73 with SMTP id n70ls1152278ioe.23.gmail; Thu, 17 Nov 2016 07:33:54 -0800 (PST) X-Received: by 10.107.1.138 with SMTP id 132mr3342527iob.72.1479396834393; Thu, 17 Nov 2016 07:33:54 -0800 (PST) Original-Received: from smtp91.ord1c.emailsrvr.com (smtp91.ord1c.emailsrvr.com. [108.166.43.91]) by mx.google.com with ESMTPS id e145si9194472itb.16.2016.11.17.07.33.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Nov 2016 07:33:54 -0800 (PST) Received-SPF: neutral (google.com: 108.166.43.91 is neither permitted nor denied by best guess record for domain of tom@honermann.net) client-ip=108.166.43.91; Original-Received: from smtp12.relay.ord1c.emailsrvr.com (localhost [127.0.0.1]) by smtp12.relay.ord1c.emailsrvr.com (SMTP Server) with ESMTP id 24F49C02A9 for ; Thu, 17 Nov 2016 10:33:54 -0500 (EST) X-Auth-ID: tom@honermann.net Original-Received: by smtp12.relay.ord1c.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 0678AC02A8 for ; Thu, 17 Nov 2016 10:33:53 -0500 (EST) X-Sender-Id: tom@honermann.net Original-Received: from [192.168.1.14] (pool-71-176-249-9.rcmdva.fios.verizon.net [71.176.249.9]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA) by 0.0.0.0:587 (trex/5.7.12); Thu, 17 Nov 2016 10:33:54 -0500 In-Reply-To: <6b73bf50-4189-4d5d-a2c0-2debb085659e@isocpp.org> X-Original-Sender: tom@honermann.net X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 108.166.43.91 is neither permitted nor denied by best guess record for domain of tom@honermann.net) smtp.mailfrom=tom@honermann.net 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:29442 Archived-At: This is a multi-part message in MIME format. --------------1ECB6F4A89B94423D6D5BA7C Content-Type: text/plain; charset=UTF-8; format=flowed On 11/17/2016 02:10 AM, TONGARI J wrote: > What about automatically generating types for string-literals? > Probably with a built-in literal operator 'lit' that does the compiler > magic. I've given this a little thought. My motivation comes from wanting to know the encoding of a string literal (e.g., implementation defined execution character set vs UTF-8). Presumably, the generated/deduced type could record this information. Such a mechanism would address the use cases that motivated P0482R0 . I think the primary difficulty with such an approach is addressing backward compatibility; in particular standard conversions and overload resolution. The generated/deduced type would have to allow implicit conversion to an (lvalue) array of code unit type (and then allow array-to-pointer decay). The potential difficulties with specifying such behavior are briefly discussed in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0482r0.html#design_compat_core. You're proposal would presumably break the following code unless special rules we're introduced to allow a different type deduction for deduced pointer types. auto *p = "text"; Tom. -- 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/08b6d632-c137-b039-9d79-7e67f9ccecfa%40honermann.net. --------------1ECB6F4A89B94423D6D5BA7C Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On 11/17/2016 02:10 AM, TONGARI J wrote:
What about automatically generating types for string-literals?
Pr= obably with a built-in=C2=A0literal operator 'lit' that does the compiler magic.
I've given this a little thought.=C2=A0 My motivation comes from wantin= g to know the encoding of a string literal (e.g., implementation defined execution character set vs UTF-8).=C2=A0 Presumably, the generated/deduced type could record this information.=C2=A0 Such a mechanism would address the use cases that motivated P0482R0.

I think the primary difficulty with such an approach is addressing backward compatibility; in particular standard conversions and overload resolution.=C2=A0 The generated/deduced type would have to all= ow implicit conversion to an (lvalue) array of code unit type (and then allow array-to-pointer decay).=C2=A0 The potential difficulties with specifying such behavior are briefly discussed in http://www.open-st= d.org/jtc1/sc22/wg21/docs/papers/2016/p0482r0.html#design_compat_core.<= br>
You're proposal would presumably break the following code unless special rules we're introduced to allow a different type deduction for deduced pointer types.

auto *p =3D "text";

Tom.

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