Re: [Qemu-devel] [PATCH 01/16] net: Add a hub net client

From: Laszlo Ersek <lersek@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>,
	Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
	Zhi Yong Wu <wuzhy@cn.ibm.com>,
	qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 01/16] net: Add a hub net client
Date: Mon, 23 Jul 2012 17:16:00 +0200	[thread overview]
Message-ID: <500D6AB0.1050703@redhat.com> (raw)
In-Reply-To: <CAJSP0QX3jbrx0ksggZFO3v0pqnir7D5wCiZmnT0WHusU0hir0w@mail.gmail.com>

On 07/23/12 16:52, Stefan Hajnoczi wrote:
> On Mon, Jul 23, 2012 at 3:05 PM, Laszlo Ersek <lersek@redhat.com> wrote:

>> The idea is, rather than
>>
>>     unsigned int id = hub->num_ports++;
>>
>> it should say
>>
>>     unsigned int id;
>>     /* ... */
>>     id = hub->num_ports++;
>>
>> ... Hm, yes, I remember it from
>> <http://www.manpages.info/freebsd/style.9.html>. But again, I'm not sure
>> how qemu treats this.
> 
> "Be careful to not obfuscate the code by initializing variables in the
> declarations.  Use this feature only thoughtfully.  DO NOT use
> function calls in initializers."
> 
> This?
> 
> Do you know the rationale?  It's not clear to me how this "obfuscates" the code.

I think the rationale is that (a) people tend to reorganize definitions,
and the expressions in the initializer lists may depend on the original
order, (b) even worse with removal of variables, (c) many people have a
"conceptual divide" between the definition block and the logic below it,
and the first should set constant defaults at most. (Naturally this
prevents C99/C++ style mixing of definitions and code as well, at least
without explicit braces.)

I'm one of those people, but again I'm not sure if qemu has any
guideline on this.

> Messing around with side-effects in a series of variable declarations
> with intializers could be bug-prone.  But here there is only one
> initializer so it's not a problem.
> 
> Regarding QEMU, there's no coding style rule against initializers.
> Personally I think that's a good thing because it keeps the code
> concise - people reading it don't have to keep the declaration in
> their mind until they hit the initializer later on.

Well I keep the definitions at the top of the block so I can very easily
return to them visually (and be sure they do nothing else than define
variables / declare externs), but it's getting philosophical :)

I have nothing against this initializer as-is, I just wanted to voice
*if* there's such a guideline in qemu *then* it should be followed :)

Thanks!
Laszlo