From -1953887343828382897 X-Google-Thread: 7894ca11fe,421cd8b98acf7c5 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!news2.glorb.com!news.alt.net!frodo.cs.rpi.edu!not-for-mail From: frege Newsgroups: comp.std.c++ Subject: Re: Why there are both complex::real and std::real? Date: Tue, 3 Nov 2009 12:26:59 CST Organization: http://groups.google.com Lines: 64 Sender: cppmods@cs.rpi.edu Approved: stephen.clamage@sun.com Message-ID: <41c3b2ca-7cbe-4637-afd1-b78e1ae0c74d@j4g2000yqe.googlegroups.com> References: <210ca399-bea2-47bf-b614-f4cef8fe25fd@k26g2000vbp.googlegroups.com> <9f639ca8-87a5-43fe-923f-c62a4bea7cfa@j4g2000yqa.googlegroups.com> <1858197e-a472-4036-8716-bf96f5a0bb34@k4g2000yqb.googlegroups.com> NNTP-Posting-Host: netlab.cs.rpi.edu Content-Type: text/plain; charset=ISO-8859-1 To: (Usenet) Return-Path: X-Original-Date: Mon, 2 Nov 2009 10:11:49 -0800 (PST) X-Submission-Address: std-c++@netlab.cs.rpi.edu Xref: g2news2.google.com comp.std.c++:1644 On Nov 1, 10:26 pm, "Joe Smith" wrote: > > I also have some namespacing concerns with free functions. Free functions > can be used in two different ways. I'll show these by example. > > namespace complex_utils{ > template > T conj(T& t) > { return T(std::real(t), -std::imag(t)); } > > } > > That sort of does not cause namespace issues. When I define my new > complex-like type that is comaptible enough that many templates designed for > std::complex can use it, I simply inject a new overload into namespace std, > which I am explicitly permitted to do. > > The other form is as follows. > > namespace soemthing{ > template > T conj(const T& t) > { return T(real(t), -imag(t)); } > > } > > Here, ADL is being used. Injecting an overload into namespace std will do > nothing here, since the compiler will be looking in my namespace for real > and imag. Thus in some sense, now I need a my_ns::real(my_complex) function, > when it is conceptually an overload of std::real, and thus ought to belong > there. In some sense then my namespace is being infringed upon. I would not > be objecting to the infringment upon the ::my_ns::my_complex namespace of > member functions, since my goal is compaibilty, but infringing the ::my_ns > namespace so that ::my_ns::my_complex can be compatible seems wrong. > template T conj(const T& t) { using namespace std; return T(real(t), -imag(t)); } I've seen this form a few times (if I recall it correctly), particularly for swap() which is sometimes injected into std::, sometimes not, depending on implementor. I think this then catches both cases, favouring the T version of real ()/imag() if it exists (via ADL). I agree with you that, in general, the right thing to do is to overload std::real(), as that is the context of what you are implementing. Otherwise a function like real(t) could be anything - not related to complex numbers at all... Tony -- [ 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 ]