220 37304 article Path: news.gmane.org!.POSTED!not-for-mail From: Miguel Ojeda Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Pointer overload for || Date: Sun, 11 Mar 2018 19:06:37 +0100 Lines: 87 Approved: news@gmane.org Message-ID: References: <1fea07df-46a6-4df2-865a-849be8f8d129@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1520791497 17550 195.159.176.226 (11 Mar 2018 18:04:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 11 Mar 2018 18:04:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDRZHGH43YJRBQXASXKQKGQEWLGTK7Y@isocpp.org Sun Mar 11 19:04:52 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f197.google.com ([209.85.216.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ev5L2-0004TR-AR for gclcip-std-proposals@m.gmane.org; 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[209.85.220.65]) by mx.google.com with SMTPS id m3sor3631325qtg.94.2018.03.11.11.06.58 for (Google Transport Security); Sun, 11 Mar 2018 11:06:58 -0700 (PDT) Received-SPF: pass (google.com: domain of miguel.ojeda.sandonis@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; X-Received: by 10.237.55.33 with SMTP id i30mr8615474qtb.202.1520791617582; Sun, 11 Mar 2018 11:06:57 -0700 (PDT) Original-Received: by 10.200.52.247 with HTTP; Sun, 11 Mar 2018 11:06:37 -0700 (PDT) In-Reply-To: <1fea07df-46a6-4df2-865a-849be8f8d129@isocpp.org> X-Original-Sender: miguel.ojeda.sandonis@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=nEqhXgrA; spf=pass (google.com: domain of miguel.ojeda.sandonis@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=miguel.ojeda.sandonis@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=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:37304 Archived-At: On Sun, Mar 11, 2018 at 9:38 AM, wrote: > Not sure how this will be received -- I haven't posted here much. Just > thought it would be worth mentioning this idea. > > Suppose you have an API that you want to optionally allocate storage for > your user. They can either pass in a pointer to some existing allocated > space, or pass in a null pointer and space is allocated for them. > > void foo(int *x) { > if (x == nullptr) { > x = new int; > } > // etc. > } > > Just figured it would be a decent idea if the || operator received a pointer > overload. Then you could write the more succinct > > void foo(int *x) { > x = x || new int; > } > > or even (ducks for cover) > > void foo(int *x) { > x ||= new int; > } Your first version is the best one, to be honest :-) In any case, if you really need something like you propose (a pseudo-DSL, generated code, ...?), then a macro with a descriptive name would be the simplest and most readable, e.g. for your second version: #define OR_ELSE(v, e) ((v) ? (v) : (e)) // ... x = OR_ELSE(x, new int); For your third version: #define ENSURE_INIT(v, e) do { if (not (v)) (v) = (e); } while(false) // ... ENSURE_INIT(x, new int); If you are really keen on having the operator, you could always approximate like: #define LAZY(x) [](){ return (x); } template T operator||(T p, E e) { if (p) return p; return e(); } // ... x = x || LAZY(new int); Similar for |=; and add something to restrict the overloads as needed. Now, if you want to make a cool proposal: template T operator||(T p, E e) { if (p) return p; return e; } // ... x = x || new int; ;-) Cheers, Miguel -- 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. 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