svn commit: r298247 - head/sbin/fdisk_pc98

[Bruce Evans]

On Wed, 20 Apr 2016, John Baldwin wrote:

> On Wednesday, April 20, 2016 01:06:38 PM Bruce Evans wrote:
>> On Wed, 20 Apr 2016, Marcelo Araujo wrote:
>>
>>> 2016-04-20 0:16 GMT+08:00 John Baldwin <jhb at freebsd.org>:
>>>
>>>> On Tuesday, April 19, 2016 04:46:13 AM Marcelo Araujo wrote:
>>>>> Author: araujo
>>>>> Date: Tue Apr 19 04:46:13 2016
>>>>> New Revision: 298247
>>>>> URL: https://svnweb.freebsd.org/changeset/base/298247
>>>>>
>>>>> Log:
>>>>>   Remove redundant parenthesis.
>>>>>
>>>>>   Submitted by:       pfg
>>>>>   MFC after:  2 weeks.
>>
>> I don't realling like churnging to the nonstandard nitems().  Use
>> of the nonstandard <sys/param.h> is bad enough.
>
> I think it's not that bad from a readability standpoint.  Other languages
> have fairly concise syntax for 'for-each' loops and this provides a
> closer variant of that for statically sized arrays.  TAILQ_FOREACH() is
> still nicer of course.  One could imagine doing some sort of
> ARRAY_FOREACH() that was:

Ugh, I really realling (sic) don't like the FOREACH macros.  The FOREACH
macros add syntactic salt.  The queue macros were bad enough before they
had FOREACH.  Arrays don't start with such nastiness.

> #define	ARRAY_FOREACH(p, array)    \
> 	for (size_t __i = 0, (p) = &(array)[0]; __i < nitems((array)); __i++, (p)++)

This only works in the not very usual case of a simple loop from the start
to the end.  Even the name EACH becomes wrong if the range is anything else.
For full nastiness, add a few hundred FORFOO macros to handle multi-
dimensional arrays with different access methods, array slices, sentinels
and other terminating conditions, etc.

> Perhaps better is this:
>
> #define	ARRAY_FOREACH(p, array)	\
> 	for ((p) = &(array)[0]; (p) < &(array)[nitems((array))]; (p)++)
>
> (No need for __i)

But hiding the indexes forces the old C programming idiom of using
pointers for everything.  A mere few hundred FORFOO macros won't do.
For just 1-dimensional FOREACH, you need 3 versions to expose p, i or
both p and i.

>> Churnging too much (also remove excessive parentheses and braces) gives:
>>
>>  	size_t i;		/* XXX: I don't like unsigned types, but... */
>>
>>  	for (i = 0; i < nitems(part_types); i++)
>>  		if (part_types[i].type == type & 0x7f)
>>  			return (part_types[i].name);
>>  	return ("unknown");
>
> This would work for me (unless folks actually like the ARRAY_FOREACH()
> idea).

Once a loop is simple enough, it is easy to see that it really is simple
without an ARRAY_FOREACH() macros that hides its details.  Actually, it
is not so simple since it has a special terminating condition.  It only
handles EACH (every) element in unusual cases.

Bruce