220 37308 article Path: news.gmane.org!.POSTED!not-for-mail From: Richard Hodges Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Pointer overload for || Date: Mon, 12 Mar 2018 08:33:51 +0100 Lines: 360 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: multipart/alternative; boundary="f403045fc23cdf5af00567322995" X-Trace: blaine.gmane.org 1520839912 22324 195.159.176.226 (12 Mar 2018 07:31:52 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 12 Mar 2018 07:31:52 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD4PBM7UWAHRBYO2TDKQKGQEN2HWPGY@isocpp.org Mon Mar 12 08:31:48 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f70.google.com ([209.85.214.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1evHvv-0005ge-QX for gclcip-std-proposals@m.gmane.org; Mon, 12 Mar 2018 08:31:48 +0100 Original-Received: by mail-it0-f70.google.com with SMTP id m37sf8276666iti.9 for ; Mon, 12 Mar 2018 00:33:54 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1520840034; cv=pass; d=google.com; s=arc-20160816; b=cKBPxA2otUL0w1x8Xgh9wgnLmIXjXqGHuy/G5OktHBgH4GIeDvSwF4eb5ENSybNN/n 3JGVaxM2e3QyMya5ujm7vegYgEGZ/NVeBaWQSPgV68a8kZpCVgaLPC6IP+WzMYnkujC0 A0HwKp0tbZh2v91jimTFgDimikbndjUmUgVcG8kdMS20hsAFaR4b9FjfGoyeQP2wtr+S B8VeB4vNrxHlxRvMzvuVAsjNs+HvZsYaqd6bvM9zSZ2W8UvTlIqT4fwmaSTQ/+pd9H0T VTtvqmSwjrqTjCm/qFXUvmbBDptr5yJIYmA7f4E27Wn+MOHa3utM4FZmDFwvU611Usy6 Z56A== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:reply-to:to:subject:message-id:date :from:references:in-reply-to:mime-version:arc-authentication-results :arc-message-signature:dkim-signature:arc-authentication-results; bh=+Lh+WnlorlHWyGlj79mSGtWczvw4Xq8vPyta/TDR5YI=; b=Dwx+DyOifRPc8t7jS4ZTyUCG709J663Gs1lqW2jds02qLATDKDO/Id0yKRXX+Sq5fq hgU+W6Xpz8mrJsIY/3HTRiXw41Z+MDdAG8Ka6VN0tPfjvi9KG0J4CEFY13JcSgbwRIVH MyAZ6l3dhj0BHl0qVgSpXmj9XBeDVJUQ4JuYj7282vE4SYUNyAc3UV22ETmHdMxghpFi actsVbm7/9piK+bNiEwhvHIeTPQNzgFko+VS/c7iIDPEibsv79uYdyZQ7UaqvcpxpQTI 72LRVn4iMPiUzy1aEHFwRrwBMfFxx7vY/ViQQh2WkUEkroFMSaSMP2IpesXcqqvymJjz d5NA== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PXzerKbG; spf=pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=hodges.r@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject: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; bh=+Lh+WnlorlHWyGlj79mSGtWczvw4Xq8vPyta/TDR5YI=; b=S96zHHqxPZ2f1yRRAJKMih7D5czzE0opjlQEvTXN3VodNGJY1/QzgthQ8tSCcOhBg3 PEXFAhJbj7o4inJBebN9f5i86lqCkDDIlRxdRV52+ODa/SHQXuBLEsKHccMSPnZrHZdZ t6Ov4GokT0HC75EIjSFSmcMamg+5ZYxd4TdMp829aiEU3kmlWnkFlbSVQ+svzpXg31Od XJAjlS5EHa4NkjZjnrxX8j8KbvWnhWx1GFnzQc3mgRpZ5cznETDe0YGGnWANxDxTr0U1 AEF7Cg5ySlgnAIyHtiAWmLDp5zP0XgRdAspoz7ZmnuU7NsLPcyXJ+D+Sxyy3EGLCdtdX G7gg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject: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=+Lh+WnlorlHWyGlj79mSGtWczvw4Xq8vPyta/TDR5YI=; b=d4ydTGFKiiwkgVdtAI3qAdMCVKatJJmpBHyEQSKV3ygv3ASR/fcqzfnKS+HvERmQRk cgF6AJ4x7zC/FiWKlJr6DQ5K2zLtEh4EaNZ88yuZ6EjBz2fvYHFTumCMEVWJ44TAubUz NoLsop2b8XW1SzKkMSxodXPKJmLgR/FPbcZKTZoXy4nTqgUdshcxDsRTNT4hMCiP4/eZ FYDDccfhD0IGqL5/W2OSIhljixQDU3Y0Pnd0irOK6BtXAWiPe6i9gRHwVB0f8Vle9LhH y0/UwvHdLHm3VDYC2IN+zrsNaj9jzCRS32L0aTieTpKNJzG27aDRhIHxSwux0Bllw8rq xBYA== X-Gm-Message-State: AElRT7GFlj4XkzbNV7R8gza+kZZsfZCUqfvfDAbQf/TcuYGYF16ubxHk ZaFkfmrYXiUgs2u9gRZwa3lIgA== X-Google-Smtp-Source: AG47ELsOaKPPQA7lTldLVn83kNaaAxznWKbLA+Qm3Gj9vFfa9PpN0Xt8vIj2ZGVSF0boeP4wHNpAPg== X-Received: by 10.36.208.196 with SMTP id m187mr3766769itg.42.1520840034054; Mon, 12 Mar 2018 00:33:54 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.213.2 with SMTP id m2ls487149iog.11.gmail; Mon, 12 Mar 2018 00:33:52 -0700 (PDT) X-Received: by 10.107.56.139 with SMTP id f133mr8092492ioa.34.1520840032548; Mon, 12 Mar 2018 00:33:52 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1520840032; cv=none; d=google.com; s=arc-20160816; b=INXC5b6/50D784j2uY0y/O7QQYS+NLAUSuN4gIZV5KzktXlicmO3yI36Ya/3Qt8ZY2 8dES79tRYG5LBm228k8DeDQGzrxTyXiwEwqKKdsA/RJMbmbz4yfb6fpfRzkKszgTWseK KTDlm49P1sJCeoMSmxka8OEH4ziSC5xnOEOXLNPR3aO16rRH32gi77Mi5mDqRv65Fz6I T2osAhnX3TkJajYMRW0zCynQXHgB6zNBThpur5MqYOvvYHEVQuu0GlWgHMP8cpOY5b+A dpBqNpT/cQS7sokU0lGs4JIJe4TNwfFdpLw3nxYCOjvSHN2CyWd4GDaw/4wVzPm5DgCE g2aA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=to:subject:message-id:date:from:references:in-reply-to:mime-version :dkim-signature:arc-authentication-results; bh=0QSfeAVvLbv8sXhkMyyGgFi3Fw4GTBV9355Vt4r7Hww=; b=CwLZHqhEB06dGIXIibFu9BxUS7DozccIqugSjGsAiaK4LSWaxWYYHzRY+aKUACu6P7 FCSd0Wn32+oQWzS0s+dv4BLve8rgUItmfH/IUEyYbauL7YOHIet3fxFCNuLvv2sGR77t OuVcWijgUlOC7RSZoZy1ukeahHKNBv+95PP0QUkq96xAao/Oyr288+7/VE+rhWWs5tPy z3epye2SOVdSNlst/UerlWyvc74/Senwv1GDPS8Uoxt62KBZaTz4A+WQoxwBz2Xvgs6a WCrjwByKFf4OOafYUhxrznFuSDKsmhEZsxSPyUNGrlzcke0WBzjO1B4CX+oMTXZrlAnl lXLA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PXzerKbG; spf=pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=hodges.r@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Original-Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id 67sor2173285ite.142.2018.03.12.00.33.52 for (Google Transport Security); Mon, 12 Mar 2018 00:33:52 -0700 (PDT) Received-SPF: pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; X-Received: by 10.36.240.77 with SMTP id p13mr6635789iti.72.1520840032081; Mon, 12 Mar 2018 00:33:52 -0700 (PDT) Original-Received: by 10.2.102.105 with HTTP; Mon, 12 Mar 2018 00:33:51 -0700 (PDT) In-Reply-To: X-Original-Sender: hodges.r@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PXzerKbG; spf=pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=hodges.r@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:37308 Archived-At: --f403045fc23cdf5af00567322995 Content-Type: text/plain; charset="UTF-8" I am a little surprised and dismayed at the eagerness to resort to macros. We can already safely overload operators with a custom generator type. No need for macros, language extensions or any other magic. live demonstration: http://coliru.stacked-crooked.com/a/bc751df610a220ce On 12 March 2018 at 01:28, wrote: > > > On Sunday, March 11, 2018 at 7:06:59 PM UTC+1, Miguel Ojeda wrote: > >> 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); >> >> > This solution is not perfect because it reuse `v` multiple times, if value > is not simply value it could be problematic. > > Better would be using lambda similar like in your next point: > > > #define OR_ELSE(v, e) ([&](auto MACRO_OR_ELSE_VALUE_X){ return (MACRO_OR_ELSE_VALUE_X > ? MACRO_OR_ELSE_VALUE_X : (e)); }(v)) > > > > This will allow evaluate `v` only once and can be inserted in other > expressions: > > auto z = h() ? OR_ELSE(OR_ELSE(x, foo()), bar()) : zz(); > > > > >> 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. > To view this discussion on the web visit https://groups.google.com/a/ > isocpp.org/d/msgid/std-proposals/c7cd5d95-0031-4e50- > b7a1-9adcff695bd2%40isocpp.org > > . > -- 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/CALvx3hYz84MdBu_WsixPmWf8N%3D9FY4BiqOv%2BLon21nF2m_f0Ow%40mail.gmail.com. --f403045fc23cdf5af00567322995 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
I am a little surprised and dismayed at the eagerness to r= esort to macros.

We can already safely overload operator= s with a custom generator type. No need for macros, language extensions or = any other magic.






On 12 March 2018 at 01:28, <inkwizytoryan= kes@gmail.com> wrote:


On Sunday, March 11, 2018 at 7:06:59 PM UTC+1, Miguel O= jeda wrote:
On Sun, Mar 11, 2018 at 9:38 AM, =C2=A0<jefferson..= ..@gmail.com> wrote:
> Not sure how this will be received -- I haven't posted here mu= ch.=C2=A0 Just
> thought it would be worth mentioning this idea.
>
> Suppose you have an API that you want to optionally allocate stora= ge for
> your user.=C2=A0 They can either pass in a pointer to some existin= g allocated
> space, or pass in a null pointer and space is allocated for them.
>
> void foo(int *x) {
> =C2=A0 if (x =3D=3D nullptr) {
> =C2=A0 =C2=A0 x =3D new int;
> =C2=A0 }
> =C2=A0 // etc.
> }
>
> Just figured it would be a decent idea if the || operator received= a pointer
> overload.=C2=A0 Then you could write the more succinct
>
> void foo(int *x) {
> =C2=A0 x =3D x || new int;
> }
>
> or even (ducks for cover)
>
> void foo(int *x) {
> =C2=A0 x ||=3D 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:

=C2=A0 =C2=A0 #define OR_ELSE(v, e) ((v) ? (v) : (e))

=C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 x =3D OR_ELSE(x, new int);

For your third version:

=C2=A0 =C2=A0 #define ENSURE_INIT(v, e) do { if (not (v)) (v) =3D (e); = } while(false)

=C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 ENSURE_INIT(x, new int);


This solution is not perfect because = it reuse `v` multiple times, if value is not simply value it could be probl= ematic.

Better would be using lambda similar like in your next point= :


#define = OR_ELSE(v, e) = ([&](auto MACRO_OR_ELSE_VALUE_X){= return (MACRO_OR_ELSE_VALUE_X ? MACRO_OR_ELSE_VALUE_X : (<= span style=3D"color:#000" class=3D"m_8675750317141035639styled-by-prettify"= >e)); }(v))

<= /span>


This will allow evaluate `v` only once and= can be inserted in other expressions:

auto z =3D h() = ? OR_ELSE(OR_ELSE(x<= span style=3D"color:#660" class=3D"m_8675750317141035639styled-by-prettify"= >, foo()), bar()) : zz();


=C2=A0=
If you= are really keen on having the operator, you could always
approximate like:

=C2=A0 =C2=A0 #define LAZY(x) [](){ return (x); }

=C2=A0 =C2=A0 template <typename T, typename E>
=C2=A0 =C2=A0 T operator||(T p, E e)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0if (p)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return p;
=C2=A0 =C2=A0 =C2=A0 =C2=A0return e();
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 x =3D x || LAZY(new int);

Similar for |=3D; and add something to restrict the overloads as needed= ..

Now, if you want to make a cool proposal:

=C2=A0 =C2=A0 template <typename T, expression E>
=C2=A0 =C2=A0 T operator||(T p, E e)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0if (p)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return p;
=C2=A0 =C2=A0 =C2=A0 =C2=A0return e;
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 x =3D x || new int;

;-)

Cheers,
Miguel

--
You received this message because you are subscribed to the Google Groups &= quot;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.
To view this discussion on the web visit = https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/c7cd= 5d95-0031-4e50-b7a1-9adcff695bd2%40isocpp.org.

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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/CALvx3hYz84Md= Bu_WsixPmWf8N%3D9FY4BiqOv%2BLon21nF2m_f0Ow%40mail.gmail.com.
--f403045fc23cdf5af00567322995-- .