From 2057817775593001320 X-Google-Thread: 7894ca11fe,bda36747929f8c7f X-Google-Attributes: gid7894ca11fe,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news2.google.com!news.glorb.com!news.alt.net!frodo.cs.rpi.edu!not-for-mail From: Scott Meyers Newsgroups: comp.std.c++ Subject: Re: How many parameters in T({x, y, z}) ? Date: Sun, 1 Nov 2009 21:26:58 CST Organization: albasani.net Lines: 37 Sender: cppmods@cs.rpi.edu Approved: stephen.clamage@sun.com Message-ID: References: NNTP-Posting-Host: netlab.cs.rpi.edu Content-Type: text/plain; charset=ISO-8859-1; format=flowed To: (Usenet) Return-Path: X-Original-Date: Sun, 01 Nov 2009 18:06:49 -0800 X-Submission-Address: std-c++@netlab.cs.rpi.edu Xref: g2news2.google.com comp.std.c++:1629 Johannes Schaub (litb) wrote: > is a braced expression list), and ends up at 13.3.1.3. So in fact the > argument in your case consists of 1 instead of 3 arguments [...] > Now, if you add the initializer list, there are two viable candidate > functions, instead of only one: The initializer list constructor, and the > copy constructor. 13.3.3.1.5 maps the conversion sequence for the > initializer list constructor to an identity conversion by 13.3.3.1.5/2. In > this case, the copy constructor is still viable, but reference binding is > going back to 13.3.3.1.5/3 again (because it converts the initializer list > to "Widget" - *not* to initializer_list which is merely a parameter of > the constructor used in the user defind conversion sequence. > > Since using the initializer list ctor results in a better conversion > sequence, it's used over the copy constructor by GCC. I think GCC does it > all right here. Given your (very impressive) analysis, I agree. It will take some time before I internalize that Widget w { a, b, c }; is a constructor call with 1 or 3 arguments (depending on the constructors offered by Widget), while Widget ({a, b, c}); is always a constructor call with 1 argument. Scott -- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@netlab.cs.rpi.edu] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ]