Subject: Re: [PATCH 1/2] add macro REALLOCARRAY

From: Jeff King <[email-masked]>
Date: Wed, 17 Sep 2014 04:17:54 -0400

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

> René Scharfe <[email-masked]> 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 <[email-masked]>
> > ---
> 
> 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