Re: [Xen-devel] [PATCH RFC v2 06/13] libxl: permit declaration after statement

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2011-11-28 at 16:40 +0000, Ian Jackson wrote:
> Stefano Stabellini writes ("Re: [Xen-devel] [PATCH RFC v2 06/13] libxl: 
> permit declaration after statement"):
> > I think it would make sense to add to the CODING_STYLE that variable
> > declarations shouldn't be mixed with code, unless part of a macro or an
> > alloca-like construct.
> 
> I think this is a silly rule.  In my proposed commit message I
> advanced three reasons for allowing declaration after statement:
> 
> > >  * It allows variables to be more often initialised as they are
> > >    declared, thus reducing the occurrence of uninitialised variable
> > >    errors.
> > > 
> > >  * Certain alloca-like constructs (arrays allocated at runtime on the
> > >    stack) can more often be written without a spurious { } block.
> > >    Such blocks are confusing to read.
> > >
> > >  * It makes it easier to write and use macros which declare and
> > >    initialise formulaic variables and do other function setup code,
> > >    because there is no need to worry that such macros might be
> > >    incompatible with each other or have strict ordering constraints.
> 
> Of these the first two improvements would be banned by your proposed
> coding style rule.
> 
> I don't understand what the harm is in allowing declarations, with
> initialisation, freely mixed with code.

Variable declarations should either be at the top of the function or
immediately before / as part of the block which uses them. e.g. this is
unhelpful:

void a_func(void)
{
        /* a bunch of code; */

        int bar;

        /* a bunch more code not using bar */

        bar = get_me_a_bar();

        /* use bar lots */
}

Ian.


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