From -2422717720121777687 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,5e0145d162a6d1d6 X-Google-Attributes: gidf78e5,public From: Srinivas Vobilisetti Subject: Re: Why is granting friendship to a templ. parameter ill-formed? Date: 1998/03/07 Message-ID: <35005B2A.7410@cs.wayne.edu>#1/1 X-Deja-AN: 331584274 Content-Transfer-Encoding: 7bit References: <6dop9s$kq6$1@news.utu.fi> X-Original-Date: Fri, 06 Mar 1998 13:23:06 -0700 X-Authentication-Warning: crchh14.us.nortel.com: news set sender to srv@cs.wayne.edu using -f Content-Type: text/plain; charset=us-ascii Organization: Bell Northern Research X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUANQCpGOEDnX0m9pzZAQGCigF9HMiaYokYCdihkycAa5QNWYbQUv2jH7I0 J1xgm6QFBtbJbQgo3fIgdTajacL4nLQD =6PqV Mime-Version: 1.0 Newsgroups: comp.std.c++ Jaakko =?UNKNOWN-8BIT?Q?J=E4rvi?= wrote: > > Hi, > > Why is this ill-formed? > > template class X { friend class T; ... > > It is clearly stated in the standard (below a clip from CD2), but what is > the reason behind it. > > /Jaakko > > 7.1.5.3 Elaborated type specifiers [dcl.type.elab] > ... > 2 ... > If the identifier (my addition: in friend class identifier) resolves to a > typedef-name or a tem- > plate type-parameter, the elaborated-type-specifier is ill-formed. > [Note: this implies that, within a class template with a template > type-parameter T, the declaration friend class T; > is ill-formed. ] > To prevent back door access to template class's private members. If you give friendship based on the template parameter, then any class can get access to the template private members thru back door (by creating an instance of the template with its type as parameter). Taking your example, my class Y can get access to private members of your template class X by creating an instance of X. Srinivas --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]