Re: [PATCH 2/2] replace-object.c: remove the_repository from prepare_replace_object

From: Junio C Hamano <gitster@pobox.com>
Date: May 10, 2018, 10:23 UTC
Message-ID: <xmqqtvrfizce.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180509234059.52156-2-sbeller@google.com>

Stefan Beller <sbeller@google.com> writes:

Show 7 quoted lines

> This was missed in 5982da9d2ce (replace-object: allow
> prepare_replace_object to handle arbitrary repositories, 2018-04-11)
>
> Technically the code works correctly as the replace_map is the same
> size in different repositories, however it is hard to read. So convert
> the code to the familiar pattern of dereferencing the pointer that we
> assign in the sizeof itself.

;-)

We say

	ptr = xmalloc(sizeof(*ptr))

is better because

	ptr = xmalloc(sizeof(typeof(*ptr)))

is easy to go stale unless we actually use typeof and instead say a concrete type like "struct oidmap".

This one was doing

	ptr = xmalloc(sizeof(*another_ptr))

and it was OK because ptr and another_ptr happened to be of the same type. I wonder if we are making it safer, or making it more obscure to seasoned C programmers, if we introduced a pair of helper macros, perhaps like these:

	#define ALLOCATE(ptr) (ptr) = xmalloc(sizeof(*(ptr)))
	#define CALLOCATE(ptr,cnt) (ptr) = xcalloc((cnt), sizeof(*(ptr)))

The change looks obviously good.  Will queue.

Thanks.