220 6766 article Path: news.gmane.org!not-for-mail From: Mikhail Semenov Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Revision of N3702: Introducing an optional parameter for mem_fn. Date: Sun, 29 Sep 2013 07:21:36 -0700 (PDT) Lines: 140 Approved: news@gmane.org Message-ID: References: <0ffade3d-ac13-434c-b20a-85d611783fc1@isocpp.org> <2284c2d2-ec8e-43fb-90e7-c43ac9dc92c2@isocpp.org> <505813ae-956c-4693-b793-2ba47107c09c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1527_15706187.1380464496782" X-Trace: ger.gmane.org 1380464496 3896 80.91.229.3 (29 Sep 2013 14:21:36 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 29 Sep 2013 14:21:36 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDC55PNFRYGRB4XOUCJAKGQEXJ55XJY@isocpp.org Sun Sep 29 16:21:40 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f200.google.com ([209.85.214.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VQHsR-0006wN-Rp for gclcip-std-proposals@m.gmane.org; Sun, 29 Sep 2013 16:21:40 +0200 Original-Received: by mail-ob0-f200.google.com with SMTP id gq1sf17606364obb.7 for ; Sun, 29 Sep 2013 07:21:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; 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 :content-type; bh=a+hLqTChYfvj4g7g8d54Xo6F5sJ0BAe+Pmzp/4p8e9U=; b=mm42yOI9csiQT+PGbw0MwSIIS8bHABLkJ8SV/c5EWEGb0akyseVNye8YpQiOTcSQR5 N17lV5UQ+LsbMPs21LcADsihgv7wkAxcbe3V12WvW5j+Dp4op2xbwbUZARgLorQAZsBP j1VZkl18I80MDyri2cmwD3sRvDfEX8frqm22zYKDX9GWkQLEXJCGLhN33FMOJ800AtGn 3HzGIGUML1xJZZddVw2wE+KLRxlk5Y/gFAW1sUFtO1pcHha36vbuElFZOrcG1b4nHj/n DWnD+jGjcJ6GsYOHgX97pkAfYuw22RuzsCmtmfHufoaAwz7LyaipmY0QpaXJW0tOv2p4 rMHg== X-Received: by 10.50.7.65 with SMTP id h1mr9175373iga.4.1380464498895; Sun, 29 Sep 2013 07:21:38 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.8.39 with SMTP id o7ls1439649iga.28.gmail; Sun, 29 Sep 2013 07:21:38 -0700 (PDT) X-Received: by 10.50.11.16 with SMTP id m16mr307910igb.0.1380464498207; Sun, 29 Sep 2013 07:21:38 -0700 (PDT) In-Reply-To: X-Original-Sender: mikhailsemenov1957@gmail.com 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:6766 Archived-At: ------=_Part_1527_15706187.1380464496782 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable N3690, page 90, example: =20 return [=3D](auto&& ... ts) { // OK: ts is a function parameter pack printer(std::forward(ts)...); .... =20 The* decltype(ts),* not* decltype(auto),* otherwise the type is not clear. =20 As for the return *-> decltype(auto)*, it was always optional for lambdas,= =20 especially it there is one return statement. =20 =20 =20 =20 =20 On Sunday, September 29, 2013 1:17:56 PM UTC+1, toma...@gmail.com wrote: > > > W dniu niedziela, 29 wrze=B6nia 2013 06:26:18 UTC+2 u=BFytkownik Jeffrey= =20 > Yasskin napisa=B3: >> >> Thanks for the proposals. The Library Evolution group in Chicago=20 >> reviewed mem_fn and concluded that it's generally not worth extending=20 >> the callable wrappers, and that users should just use lambdas in=20 >> nearly all cases. C++14's generic lambdas with variadic captures make=20 >> this an even better tradeoff (note, I didn't compile this):=20 >> >> double r =3D integrate=20 >> ([&a](const auto&... args) { return a.fa(args...);},=20 >> x1, x2, y1, y2, z1, z2, a1, a2, b1, b2);=20 >> >> To work with any parameter/return (references) type combination, this=20 > should be written as: > double r =3D integrate( > [&a](auto&&... args) -> decltype(auto) > { return a.fa(std::forward(args)...); }); > > Which is pretty less readable and less intent clear than: > double r =3D integrate(std::mem_fn(&A::a, std::ref(a))); > > In my opinion the deifference between this 2 cases may be compared with= =20 > the diference between using > hand-writtern loop versus algorithm. > --=20 ---=20 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 e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. ------=_Part_1527_15706187.1380464496782 Content-Type: text/html; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable
N3690, page 90, example:
 
<= font face=3D"LMMono9-Regular" size=3D"1">

return [=3D](auto&& ... ts) { // OK: ts i= s a function parameter pack
printer(std::forward<decltype(ts)>(ts)= ....);

...

 

The decltype(ts), not decltype(auto), otherwise = the type is not clear.

 

As for the = return -> decltype(auto), it= was always optional for lambdas, especially it there is one return stateme= nt.

 

 

 

 

 

On Sunday, September 29, 2013 1:17:56 PM UTC+1, toma.= ...@gmail.com wrote:

=
W dniu niedziela, 29 wrze=B6nia 2013 06:26:18 UTC+2 u=BFytkownik Jeffre= y Yasskin napisa=B3:
Thanks for the proposals. = The Library Evolution group in Chicago
reviewed mem_fn and concluded that it's generally not worth extending
the callable wrappers, and that users should just use lambdas in
nearly all cases. C++14's generic lambdas with variadic captures make
this an even better tradeoff (note, I didn't compile this):

 double r =3D integrate
              ([&a](const auto&a= mp;... args) { return a.fa(args...);},
                 x1, x2, y= 1, y2, z1, z2, a1, a2, b1, b2);

To work with any parameter/return (references) type c= ombination, this should be written as:
 double r =3D integrate(
    = ;          [&a](auto&&= amp;... args) -> decltype(auto)
          &n= bsp;   { return a.fa(std::forward<decltype(auto)>(args)...)= ; });

Which is pretty less readable and less intent clear tha= n:
 double r = =3D integrate(std::mem_fn(&A::a, std::ref(a)));

In my opinion the deifference between this 2 cases may be c= ompared with the diference between using
hand-writtern loop versus algor= ithm.

--
 
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