220 39026 <29394898-f878-45ad-b21c-b589e4a36caf@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Justin Bassett Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: __COLUMN__ macro to parallel __LINE__ Date: Sun, 8 Jul 2018 15:20:32 -0700 (PDT) Lines: 137 Approved: news@gmane.org Message-ID: <29394898-f878-45ad-b21c-b589e4a36caf@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_102548_978908373.1531088432908" X-Trace: blaine.gmane.org 1531088308 22710 195.159.176.226 (8 Jul 2018 22:18:28 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 8 Jul 2018 22:18:28 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC5PL3NYWEDBBMM4RLNAKGQEHGKPAPI@isocpp.org Mon Jul 09 00:18:24 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f198.google.com ([209.85.213.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fcI0d-0005nz-Qq for gclcip-std-proposals@m.gmane.org; Mon, 09 Jul 2018 00:18:24 +0200 Original-Received: by mail-yb0-f198.google.com with SMTP id s14-v6sf16223535ybg.7 for ; Sun, 08 Jul 2018 15:20:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=59c3RSWFePt6JCKQHDv/khyGNQMOFdigyqeQeVBtsYU=; b=XVGxlamgicLIrQ3wOG/WpEh6vxVw1Er6ObzxovEev398PADfRnnuefhRG+fkholQqk DMpB0V5yfUmhFbJH9r2Dz2CsbJOz7D4xrF7GgZMijJSPktuSZT99nx6L8rTsUbkzn0sa C8hKhZoMH2CPH0ELdQJjP7+B+C5ZXga9m8rxr+TxBmA27fF0dNOu4iXn/KExhOxAgs+W iyJqkvWGV/H83bDqRv7DRpNe1tqCiH5/BimbrMzqJaeFI8gVcs25+yem3NDu61ghn+Os PkZF708d2105NRyfEuMj72h1KtXa45QizI8mT0pg9ChFGaxQGTCPdclURDUiYYeOQjSO pPDQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=59c3RSWFePt6JCKQHDv/khyGNQMOFdigyqeQeVBtsYU=; b=C04u55nwbE/S1/MSs9sYmGFKUyenjlXWjF0sgcLRBC/GZhjy4gRsqvfQcO5GDLik3T 9QtoWclNn8AoVrotu24cbVp8oUgeQXlji415AIqMSK6lS6pUA3tYPLGU5uTbvEfSQ4uP PYTfa0Sfp4pDTztGF2ZSyyw1FzBnhwxUUY+9S3BP8KuYhRG3qc6snpPGl7nRDDi33uVg UNo3Nc5uvmrLgw9aRPFb9QKjFqk1r2whK17abvEXoSoJgmZ4g3jQEHIu7yhArOGy3o6T Kzol4hIrZpZDuBqD5Rqc8vAJz57scfhnsBAck99TmtOl8drCI/dQufW4WNKKJ8e0HpKf nYGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id: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=59c3RSWFePt6JCKQHDv/khyGNQMOFdigyqeQeVBtsYU=; b=sd/5sR0pmBOzpJ+EXvFnRhOK/mowFdx5R4Vq2aUfeRVDeWHMGJDtm30B8nsKDBnsEZ 1/8LbQFMS9+A00RxkSdulES0kRAf86RTuBc90DTnAd/5Q+WqMC/YYQHiq6J4VSJ1ihr1 LQPOH8Bqd9ihagBJDcqSUt+AmEWGVuGDQtbTpQDJjMp7K0D/0R8F3jAWelh1wnby8RT/ +iGaRfbeHKNJ6YG2PtdlFCeDK19sECUeB/ibRWceYXi9+cUtxhae5J659ZFdS8bllqIA SWiDNo4078x+FYeVZJUSmMjFwftBpZTQY4u+vk5WDzmdtpjnWRus3XHngypxLQ8Mfhr3 tUvg== X-Gm-Message-State: APt69E1y2PulHBdxhUv52dICkNeY7ZaZRWQaQsRvGThGVZ7BPtP7UzaR ENagzQ+YnNBAdWoIX7nHzk8IAw== X-Google-Smtp-Source: AAOMgpdadILBBP2E27N2t5QoWHk+Iil1DitBlJ9HxizvoZsdZ9Uz43MTWKKDONybKXNz5/8oPdyhmQ== X-Received: by 2002:a25:1e87:: with SMTP id e129-v6mr5547183ybe.48.1531088434757; Sun, 08 Jul 2018 15:20:34 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:320d:: with SMTP id y13-v6ls3476739yby.5.gmail; Sun, 08 Jul 2018 15:20:33 -0700 (PDT) X-Received: by 2002:a25:8203:: with SMTP id q3-v6mr2540657ybk.1.1531088433268; Sun, 08 Jul 2018 15:20:33 -0700 (PDT) X-Original-Sender: jbassett271@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:39026 Archived-At: ------=_Part_102548_978908373.1531088432908 Content-Type: multipart/alternative; boundary="----=_Part_102549_937995187.1531088432909" ------=_Part_102549_937995187.1531088432909 Content-Type: text/plain; charset="UTF-8" We have a __LINE__ macro which expands to the source file line number. Why not also have __COLUMN__ which expands to the column number? There are some cases where a unique identifier is desirable, such as SCOPE_EXIT. Currently, this identifier has to be generated either by __LINE__ or by __COUNTER__, but both have drawbacks: __LINE__ means you can't define two on the same line and __COUNTER__ is a recipe for ODR violations when used in inline functions in header files. Regardless, people do use these: #define CONCAT_IMPL(A, B) A ## B #define CONCAT(A, B) CONCAT_IMPL(A, B) #define UNIQUE_NAME CONCAT(some_prefix_, __LINE__) // or #define UNIQUE_NAME CONCAT(some_prefix_, __COUNTER__) A __COLUMN__ macro would make unique identifiers possible with none of the drawbacks of __LINE__ or __COUNTER__: // Given a ternary preprocessor CONCAT #define UNIQUE_NAME CONCAT(some_prefix_, __LINE__, __COLUMN__) I know about std::experimental::source_location, but it's not a macro, so it can't do this. -- 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/29394898-f878-45ad-b21c-b589e4a36caf%40isocpp.org. ------=_Part_102549_937995187.1531088432909 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
We have a __LINE__ macro which expands to the source file = line number. Why not also have __COLUMN__ which expands to the column numbe= r?

There are some cases where a unique identifier is des= irable, such as SCOPE_EXIT. Currently, this identifier has to be generated = either by __LINE__ or by __COUNTER__, but both have drawbacks: __LINE__ mea= ns you can't define two on the same line and __COUNTER__ is a recipe fo= r ODR violations when used in inline functions in header files. Regardless,= people do use these:

= #define CON= CAT_IMPL(A, B) A ## B
#define= CONCAT(A, B) CONCAT_IMPL(A, B)

#define UNIQUE_NAME CONCAT(some_prefix_, __LINE__)
// or
#define UNIQUE_NAME CONCAT= (some_prefix_, __COUNTER__)

A __COLUMN__ macro= would make unique identifiers possible with none of the drawbacks of __LIN= E__ or __COUNTER__:

<= span style=3D"color: #800;" class=3D"styled-by-prettify">// Given a ternary= preprocessor CONCAT
#define UNIQUE_NAME CONCAT(some_pr= efix_, __LINE__, __COLUMN__)

I know about std::experimental::source= _location, but it's not a macro, so it can't do this.

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