On Wed, Dec 17, 2008 at 01:29:02PM +0100, Jim Meyering wrote:
"Daniel P. Berrange" <berrange@redhat.com> wrote:
On Fri, Dec 12, 2008 at 09:58:32AM +0100, Jim Meyering wrote:
I propose to allow (encourage, even) the use of the standard C99 type, bool, in libvirt, but not in public interfaces[1]. There are already uses in cgroup.c and xmlrpc.c, as well as those in the gnulib "c-ctype.h" header which is included from many of libvirt's .c files.
The motivation is to make the code as readable as possible. When you see the declaration of an "int" variable, member, or function, that type gives you no clue whether it is used as a boolean. If you see a few uses that treat it as boolean, that's still no guarantee, and it may be non-trivial to ensure that there isn't some non-boolean value with a special meaning.
However, if you see a "bool" variable, you do have that guarantee.
I don't particularly like the idea of using the bool type
- No system header files use it
Of course. Can't use it there for the same reason that we wouldn't use it in libvirt's own public interfaces, as I explained. But public interfaces make up such a small fraction of the code in question that it'd be a shame to impose its restrictions on all the rest.
- Library header files which use a boolean type have nearly all defined their own custom bool types, not using stdbool.h and there's no guarentee that stdbool's idea of 'true' matches the other apps'
This is the same fundamental restriction. "bool" cannot be used in public headers.
- We don't use it in the public API, or on the wire for the remote protocol, since it has undefined size.
Same point.
- The GNULIB bool emulation is unable to provide equivlance between C's idea of true (any non-zero value) and the defined 'true' constant (whose value is 1)
That sounds scary, but isn't an issue in practice. The uses of "true" and "false" are typically only for initialization. IMHO, one should never compare a bool-declared variable to "true" or "false".
Ok, if you want to re-post the HACKING file also mentioning that 'bool' shouldn't be used in our public APIs & wire protocol, and that 'true' / 'false' should only be used for initialization I'm fine with the rest of the docs. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|