From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kamil Dudka Subject: Re: [PATCH] add warnings enum-to-int and int-to-enum Date: Wed, 2 Sep 2009 21:58:14 +0200 Message-ID: <200909022158.14425.kdudka@redhat.com> References: <20090830153202.4dc5c58c@s6510> <20090902185644.GA5148@josh-work.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:40269 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752248AbZIBT71 (ORCPT ); Wed, 2 Sep 2009 15:59:27 -0400 In-Reply-To: Content-Disposition: inline Sender: linux-sparse-owner@vger.kernel.org List-Id: linux-sparse@vger.kernel.org To: Daniel Barkalow Cc: Josh Triplett , Stephen Hemminger , linux-sparse@vger.kernel.org On Wednesday 02 of September 2009 21:19:46 Daniel Barkalow wrote: > On Wed, 2 Sep 2009, Josh Triplett wrote: > > On Wed, Sep 02, 2009 at 02:43:52PM -0400, Daniel Barkalow wrote: > > > On Wed, 2 Sep 2009, Kamil Dudka wrote: > > > > On Wednesday 02 of September 2009 19:56:47 Daniel Barkalow wrote: > > > > > It feels to me like the explicit numeric values are what make these > > > > > constants sensible to use directly as ints, and that it's only > > > > > sensible to use a non-constant value of an enum type as an int > > > > > (without an explicit cast) if all of the enum values have explicit > > > > > numeric values. > > > > > > > > > > I think: > > > > > > > > > > enum { > > > > > my_register_zero > > > > > ... > > > > > my_register_twdr > > > > > my_register_twcr > > > > > ... > > > > > }; > > > > > > > > > > void () { > > > > > write_register(my_register_twdr, SETUP_TWDR); > > > > > } > > > > > > > > > > is asking for trouble in a way that this warning is about. > > > > > > > > Both examples are too abstract for me -- missing declaration > > > > of write_register(), etc. Please attach a minimal example as a file > > > > which I can compile and test. I'll check if the "trouble" is covered > > > > by the warnings or not, and perhaps implement what's missing. Thanks > > > > in advance! > > > > > > enum { > > > foo, > > > bar > > > }; > > > > > > enum { > > > baz = 1, > > > qux = 2 > > > }; > > > > > > void test(void) { > > > int i = bar; // warn on this > > > int j = qux; // okay > > > } > > > > > > (Leaving aside the issue of whether the enum is anonymous) > > > > > > In the "bar" case, an additional value added somewhere in the list > > > (particularly if the list were long) might change "i" in a way that > > > wouldn't necessarily be obvious to users of "i". In the "qux" case, "j" > > > would only change if the "qux = 2" line were changed. > > > > I disagree with this. In both cases, you've declared an anonymous enum, > > and then used its values as constants. In the former case, you might > > just not care about the values except to compare against each other; > > granted, you ought to use a named enum rather than an int in that case, > > but nevertheless much code exists that uses int instead of enum types. > > I think anonymous vs named enums are one thing that should affect whether > you get a warning, and explicit values vs implicit values are another > factor, but I don't have an opinion on which way they should combine. > Probably either using an explicit value or an anonymous enum should be > okay by default, and the test above should use named enums. I think type-checking is the way to go, not values checking... Once you start to count with "explicit" vs. "implicit" enum values, you will sooner or later run in troubles like this: enum { A, B = 3, C, D = A + 7 }; enum { Z = (C < D) ? A : B }; Kamil