220 37307 article Path: news.gmane.org!.POSTED!not-for-mail From: inkwizytoryankes@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Pointer overload for || Date: Sun, 11 Mar 2018 17:28:34 -0700 (PDT) Lines: 300 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/mixed; boundary="----=_Part_12969_1243461468.1520814514135" X-Trace: blaine.gmane.org 1520814395 3195 195.159.176.226 (12 Mar 2018 00:26:35 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 12 Mar 2018 00:26:35 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDDLTAGNTIBBBM4TS7KQKGQEESW2P2A@isocpp.org Mon Mar 12 01:26:31 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f69.google.com ([209.85.213.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1evBIL-0000gU-O1 for gclcip-std-proposals@m.gmane.org; Mon, 12 Mar 2018 01:26:30 +0100 Original-Received: by mail-vk0-f69.google.com with SMTP id l71sf5369742vki.6 for ; Sun, 11 Mar 2018 17:28:36 -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:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=yndiy487pfi9A0DrmEsQb6TAzaSI7y3ROMbHYIg/jpg=; b=d6/ooZPSRp3qm0VVgZim9bLt6nrwPbyiZ0qPI0Rx5kL9duH+Zc73oiCXyTZh47c8ET pJW3DRr9G59teUPNGHgxSShwvYNJXiGZ+CQxixoMSBFDYGqPVh5FQVMulI9jsATmt4tM 2dnEf60UqFLXZ4zDjSe3nAwzUMmxv6nS3GV5XD0SGLAQNF9Rbvsfrh62X2x49Q1ZpBFP uzslkiO3Z6NiBjQVKDFAKA1/pP1TlI3Q+kx7S4neDqvNBEWpwEYXBJD5ACV8HhWh6oMf XzwBuIEdBprhYIgU6sLEPmsnwEuG38AOdzuxH6RSIAw9Wf0xfkz1TLNcXecljTdIW5A1 PFEw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=yndiy487pfi9A0DrmEsQb6TAzaSI7y3ROMbHYIg/jpg=; b=qDXMmx2q/xJ7zz7MHMvWjIXrkjK4gNj4JYV3RxJ6Y8W3mLi7SD791qgq6JIznefS5p PfQXYnheR0F7o02cNnxliCvy2Vk1n5yMTOEvcr1OV49KE6Lx2BsYcnKVDdWQUitGPM5D iwnNAKWqEES4ju69ZrvgjuXfrp1ab0Wlc2jFGbt8/0mqRSg6nm49nk/LqIHt9G9Rgopp vgEjgvGFD0A+/GUav/qJ8v3K6UVg3c1LNpiaMr3DOeP0w9dHPAn//lxkX9FAJve6f7wa kdfhAWQa4D8rtF8cpkqkR3/hHFCYbVWchXi7+fUubyv9tfHWceBhUYetftiZnfG5cDy7 fVYw== 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: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=yndiy487pfi9A0DrmEsQb6TAzaSI7y3ROMbHYIg/jpg=; b=b7sxJDwP+Ny0Gg6Jx42gB7TQcQ/x0/SdIB89VhGPFofFDBvu1/TW/yygxrKVWqqGBB 0a9N77DuGcJFmzHmYCwchoYnKXG0JrWZOu8Nru1LaX+cPkBSbXzDNVICXT70Ni9nksA1 3cDXIlSCacvs8udyNGjqxi4yzEEjfqrhEfIcRj0dzVC4aexAwtrt+kz+D+38pxLOAXqg /z6EAFcNI0ZXQU1LYd4FmeH2KWf/Fuq0h5y/arDfbC/i2OGIbzxJ9o07M8xtroZ1gJiq 3vNpmZ7/2sXDAzOuVma0mtdqbgg8mso16odyh1xyF1MEJUi3BZxGPFSNqBharvGMQtXS EpLQ== X-Gm-Message-State: AElRT7EZBpNdTS6YS9huzAAttzvmhnPDIWP3ZRH5rhjLd0GlTFOSeaE5 gZBsxNzx27rtRMRmtgkLX5AiKw== X-Google-Smtp-Source: AG47ELv5/797wmj2Kl10c6gvO2+JkmSQywiRz2tl/0DPNV89HoACerMPyCLEyj7eIRrtL3TLS8edCw== X-Received: by 10.31.148.73 with SMTP id w70mr2817679vkd.117.1520814516227; Sun, 11 Mar 2018 17:28:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.185.202 with SMTP id j193ls6622044vkf.18.gmail; Sun, 11 Mar 2018 17:28:34 -0700 (PDT) X-Received: by 10.31.178.81 with SMTP id b78mr811522vkf.14.1520814514738; Sun, 11 Mar 2018 17:28:34 -0700 (PDT) In-Reply-To: X-Original-Sender: inkwizytoryankes@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:37307 Archived-At: ------=_Part_12969_1243461468.1520814514135 Content-Type: multipart/alternative; boundary="----=_Part_12970_1220829327.1520814514135" ------=_Part_12970_1220829327.1520814514135 Content-Type: text/plain; charset="UTF-8" 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. ------=_Part_12970_1220829327.1520814514135 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Sunday, March 11, 2018 at 7:06:59 PM UTC+1, Mig= uel Ojeda 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=A0Just
> 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=A0They 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=A0Then 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 problematic.
<= br>Better would be using lambda similar like in your next point:


= #define OR_ELSE(v, e) = ([&](a= uto MACRO_= OR_ELSE_VALUE_X){ return (MACRO_OR_ELSE_VALUE_X ? MACRO_OR_ELSE_VALUE_X <= span style=3D"color: #660;" class=3D"styled-by-prettify">: (e)); }(v))



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

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


=C2=A0
If you are really keen on hav= ing 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

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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.
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