From -5424270311269842147 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 109fba,ac06fef48c3c04df X-Google-Attributes: gid109fba,public X-Google-Thread: f78e5,ac06fef48c3c04df X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1995-01-26 03:04:13 PST Newsgroups: comp.lang.c++,comp.std.c++ Path: nntp.gmd.de!newsserver.jvnc.net!yale.edu!yale!yale!gumby!newsxfer.itd.umich.edu!gatech!psuvax1!uwm.edu!msunews!harbinger.cc.monash.edu.au!news.cs.su.oz.au!metro!news From: maxtal@physics.su.OZ.AU (John Max Skaller) Subject: Re: friends and local classes Message-ID: Sender: news@ucc.su.OZ.AU Nntp-Posting-Host: physics.su.oz.au Organization: School of Physics, University of Sydney, Australia References: <3g0kgm$gue@engnews2.Eng.Sun.COM> Date: Thu, 26 Jan 1995 11:04:13 GMT Lines: 57 Xref: nntp.gmd.de comp.lang.c++:88095 comp.std.c++:11260 In article fenster@ground.cs.columbia.edu (Sam Fenster) writes: > >clamage@Eng.Sun.COM (Steve Clamage) writes: > >> Who said local classes are a good idea? I think they are pointless.[...] A >> number of people on the C++ Committee would like to eliminate member >> functions from local classes (myself included), although I don't expect that >> to happen. > >Let's say you want to guarantee that some action takes place when a function >exits, regardless of whether it's by any of a number of return statements, >falling off the end, or because of an exception. The only way is to create a >local object with a destructor that performs the action. That destructor must >have the function's local variables in its scope: > > void f () { > // ... > class On_Exit {~On_Exit() {delete foo; close(bar); baz--;};} on_exit; > // ... > } > >When Bjarne made "int i;" an executable statement so it could be put anywhere >in a block, his rationale was that things should be declared where they are >used. The same goes for a class that is created for a local purpose. And >such classes must be allowed to have member functions. > >Ideally, we'd have local functions too, for similar reasons (e.g. a comparison >function to pass to "qsort"). I don't expect that soon. But let's not get >rid of local classes, OK? If you want a "real" C++ compiler, try Metaware High C/C++. It not only support nested (local) functions, but has a full closure type. Sigh. In C++ almost everything except functions can be nested. I consider that a gratuitous omission destroying the orthogonality of the language. To me it is plain daft to provide full object orientation and skip over the most basic structured programming ideas. Structured programming may not be enough, but in two decades of research and experience we have learned, surely, that "flat" languages like C and Cobol and Fortran have severe problems. Now we have C++ which is "flat", but allows you to break the global "flat" space up into little bits. (objects). So we have not learned that localisation and anonymity are powerful ideas. All we've done is permit partitioning the flat space. And I contend that _that_ is not enough: within an object, we just have a miniture version of C, Cobol, or Fortran. Gak. -- JOHN (MAX) SKALLER, INTERNET:maxtal@suphys.physics.su.oz.au Maxtal Pty Ltd, 81A Glebe Point Rd, GLEBE Mem: SA IT/9/22,SC22/WG21 NSW 2037, AUSTRALIA Phone: 61-2-566-2189