Re: [PATCH v2 05/10] log-tree: use ref_namespaces instead of if/else-if

From: Derrick Stolee <derrickstolee@github.com>
To: Junio C Hamano <gitster@pobox.com>,
	Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, me@ttaylorr.com, vdye@github.com,
	steadmon@google.com, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [PATCH v2 05/10] log-tree: use ref_namespaces instead of if/else-if
Date: Thu, 4 Aug 2022 10:50:57 -0400	[thread overview]
Message-ID: <96cf691b-5190-5ba7-d612-e8473055c45c@github.com> (raw)
In-Reply-To: <2d24b539-a5b8-ed7d-2320-97588854eb5b@github.com>

On 8/4/2022 10:34 AM, Derrick Stolee wrote:
> On 8/4/2022 9:31 AM, Derrick Stolee wrote:
>> On 8/3/2022 2:31 AM, Junio C Hamano wrote:

>>> Very nice.  The double-dash in the NAMESPACE__COUNT constant somehow
>>> looks strange.  As we scan through ref_namespace[] array densely,
>>>
>>> 	for (i = 0; i < ARRAY_SIZE(ref_namespace); i++)
>>> 		...
>>>
>>> without having to use the constant would probably be more in line
>>> with the way how the rest of the codebase works.
>>
>> Ah, I did not know about that trick. Thanks!
> 
> ...except that it doesn't work because the array is declared as
> 'extern' so we don't know its size outside of refs.c.
> 
> This motivates the use of NAMESPACE__COUNT (and the double
> underscores differentiates the "COUNT" from other namespaces, so
> there is no confusion about "COUNT" being a namespace). If there
> is another way around this, then I would love to hear it!

My current workaround is to define the size of the array in the
header file:

---

enum ref_namespace {
	NAMESPACE_HEAD,
	NAMESPACE_BRANCHES,
	NAMESPACE_TAGS,
	NAMESPACE_REMOTE_REFS,
	NAMESPACE_STASH,
	NAMESPACE_REPLACE,
	NAMESPACE_NOTES,
	NAMESPACE_PREFETCH,
	NAMESPACE_REWRITTEN,

	/* Must be last */
	NAMESPACE__COUNT
};

/* See refs.c for the contents of this array. */
extern struct ref_namespace_info ref_namespaces[NAMESPACE__COUNT];

---

Then ARRAY_SIZE(ref_namespaces) works properly.

Thanks,
-Stolee