From 6045905002546086519 X-Google-Language: ENGLISH,ASCII X-Google-Thread: f78e5,fbe10986a90d9275,start X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2004-01-19 08:07:44 PST Path: archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!mutlu.news.demon.net!demon!mail2news.demon.co.uk!devnull From: omarshaikh71@yahoo.com (Omar Shaikh) Newsgroups: comp.std.c++ Subject: Proposal for adding two keywords for explicit modification Date: Mon, 19 Jan 2004 16:07:42 +0000 (UTC) Lines: 113 Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: <20040119114736.63476.qmail@web20904.mail.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable X-Trace: mail2news.demon.co.uk 1074528462 10406 10.0.0.1 (19 Jan 2004 16:07:42 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Mon, 19 Jan 2004 16:07:42 +0000 (UTC) X-Received: from mulga.cs.mu.oz.au ([128.250.1.22]) by news.demon.co.uk with esmtp (Exim 4.12) id 1AibwD-0002hY-00 for mail2news@news.news.demon.net; Mon, 19 Jan 2004 16:07:42 +0000 X-Received: from mulga.cs.mu.OZ.AU (localhost [127.0.0.1]) by mulga.cs.mu.OZ.AU with ESMTP id i0JG7dmC023916; Tue, 20 Jan 2004 03:07:39 +1100 (EST) X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id i0JG7dbC023907; Tue, 20 Jan 2004 03:07:39 +1100 (EST) X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Path: comp-std-cpp-robomod!not-for-mail X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Delivered-To: std-c++@ucar.edu X-Spam-Level: X-Spam-Status: No, hits=1.0 required=5.2 tests=FROM_ENDS_IN_NUMS autolearn=no version=2.60-mulga_r1 X-Spam-Checker-Version: SpamAssassin 2.60-mulga_r1 (1.212-2003-09-23-exp) on mulga.cs.mu.OZ.AU X-Newsgroups: comp.std.c++ X-MIME-Autoconverted: from 8bit to quoted-printable by mulga.cs.mu.OZ.AU id i0JG7dmC023916 Xref: archiver1.google.com comp.std.c++:889 Hello, all I have a suggestion to make that I believe should be a very useful addition to the C++ programming language. Please do let me know if what I have to suggest makes sense, and any suggestion would be definitely welcome. The whole purpose of this addition to the language is to prevent _accidental_ over-writing of a value, since this facility allows one to over-write only explicitly (explicit modification). I have faced the need for a feature of this sort many times; thus this suggestion. Sometimes, a constant should be modifiable, though this may sound like a contradiction. A const is too "stiff," while a variable is too unsafe. A middle path is, therefore, called for. I would like to suggest two keywords: freeze and thaw, which should fill in that need. Consider the following example to see how these two keywords work. main () { freeze int i =3D 10; // Declaring a "frozen" variable, =93freeze int i at 10=94 freeze j =3D 20; // Implicitly an int freeze int k(30); // Constructor syntax also works // what won't work freeze int m; // ERROR -> Freeze m at what value? Initialization is necessary! double arr[i]; // ERROR -> A freezable variable is NOT a constant, // so cannot be used for array declarations i =3D 40; // ERROR -> i is "frozen,=94 you cannot change it! thaw i =3D 50; // Ok to "thaw" a frozen variable and immediately change it i =3D 60; // Oops! i is frozen again! } We could simulate this behaviour in a class using methods to "thaw" the frozen value. This method, however, turns out to be very cumbersome since overloaded operators would have to be defined not just for every conceivable operation, but also for all the primitive types in the language. Secondly, any attempt to modify a frozen value should immediately give a syntax error. In the case of a class, however, only a run-time exception would be possible, defeating the concept of early error detection. Another feature of a freezable is that it should be thawable only within its own block or any underlying block. Outside its own block, its reference can only be read into a "more severe" type like a const. Take the following example: class Foo { freezable int x; public: Foo () : x(10) {} freezable int& GetRef () { return x; } void Changex (int); }; int main () { Foo f; int& i =3D f.GetRef(); // Error! Cannot read into a modifiable variable. freezable int& j =3D f.GetRef(); // Error! Not enough "severity." const int& k =3D f.GetRef(); // Works fine since k is a const } void Foo::Changex (int new_val) { // ok to thaw and change a frozen here since // this block is within x's declaration block thaw x =3D new_val; } The reason that a freezable reference can only be read into a const is that freezable data - for all=20 practical purposes - is a constant to outsiders, and is meant to be thawed and modified only by its=20 owner. I would appreciate any further suggestions / remarks on this. Thank you Omar __________________________________ Do you Yahoo!? Yahoo! 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