Re: [PATCH 1/2] add macro REALLOCARRAY

From: Jeff King <peff@peff.net>
Date: Sep 17, 2014, 08:17 UTC
Message-ID: <20140917081753.GC16200@peff.net>
In-Reply-To: <xmqqtx487nej.fsf@gitster.dls.corp.google.com>

On Mon, Sep 15, 2014 at 11:24:04AM -0700, Junio C Hamano wrote:

Show 21 quoted lines

> René Scharfe <l.s.r@web.de> writes:
> 
> > The macro ALLOC_GROW manages several aspects of dynamic memory
> > allocations for arrays: It performs overprovisioning in order to avoid
> > reallocations in future calls, updates the allocation size variable,
> > multiplies the item size and thus allows users to simply specify the
> > item count, performs the reallocation and updates the array pointer.
> >
> > Sometimes this is too much.  Add the macro REALLOCARRAY, which only
> > takes care of the latter three points and allows users to specify the
> > number of items an array can store directly.  It can increase and
> > also decrease its size.  Using this macro avoids duplicating the
> > array pointer name and takes care of item sizes automatically.
> >
> > Signed-off-by: Rene Scharfe <l.s.r@web.de>
> > ---
> 
> Makes sense.  Originally I had two minor gripes against this
> 
>  #1 a macro that modifies its arguments feels a bit too magical, and
>     we would not want to overuse them.

This is probably getting into the too-magical territory, but I have long considered a macro like:

  #define ALLOC(x) (x) = xmalloc(sizeof(*x))

to prevent obvious size-mismatch errors. You could even call the macro NEW() if you wanted to be really disgusting. :)

I rejected it as probably too cutesy (and non-idiomatic for experienced C programmers), but I feel like this REALLOC_ARRAY is basically the same thing. I dunno. It does make the code a bit more readable, once you understand what the macro is doing.

-Peff