From: Phillip Wood <phillip.wood123@gmail.com>
To: Glen Choo <chooglen@google.com>,
Linus Arver via GitGitGadget <gitgitgadget@gmail.com>,
git@vger.kernel.org
Cc: Linus Arver <linusa@google.com>
Subject: Re: [PATCH 1/5] trailer: separate public from internal portion of trailer_iterator
Date: Tue, 8 Aug 2023 13:19:13 +0100 [thread overview]
Message-ID: <1fd1f22d-e0db-04f3-7235-899b10909c7a@gmail.com> (raw)
In-Reply-To: <kl6l8rama6yj.fsf@chooglen-macbookpro.roam.corp.google.com>
On 07/08/2023 22:16, Glen Choo wrote:
> As someone who isn't that familiar with trailer code, and will have less
> time for the ML soon, this is more of a quick drive-by..
This is a bit of a drive-by comment as well ...
> "Linus Arver via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> +#define private __private_to_trailer_c__do_not_use
>> +
>> void trailer_iterator_init(struct trailer_iterator *iter, const char *msg)
>> {
>> struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
>> strbuf_init(&iter->key, 0);
>> strbuf_init(&iter->val, 0);
>> opts.no_divider = 1;
>> - trailer_info_get(&iter->info, msg, &opts);
>> - iter->cur = 0;
>> + trailer_info_get(&iter->private.info, msg, &opts);
>> + iter->private.cur = 0;
>> }
>> --- a/trailer.h
>> +++ b/trailer.h
>> @@ -119,8 +119,10 @@ struct trailer_iterator {
>> struct strbuf val;
>> ...
>> /* private */
>> - struct trailer_info info;
>> - size_t cur;
>> + struct {
>> + struct trailer_info info;
>> + size_t cur;
>> + } __private_to_trailer_c__do_not_use;
>> };
>
> Interesting approach to "private members". I like that it's fairly
> lightweight and clear. On the other hand, I think this will fail to
> autocomplete on most people's development setups, and I don't think this
> is worth the tradeoff.
>
> This is the first instance of this I could find in the codebase.
We have something similar in unpack_trees.h see 576de3d9560
(unpack_trees: start splitting internal fields from public API,
2023-02-27). That adds an "internal" member to "sturct unpack_trees" of
type "struct unpack_trees_internal which seems to be a easier naming scheme.
> I'm not
> really opposed to having a new way of doing things, but it would be nice
> for us to be consistent with how we handle private members. Other
> approaches I've seen are:
>
> - Using a "larger" struct to hold private members and "downcasting" for
> public users (struct dir_iterator and struct dir_iterator_int). I
> dislike this because I think this enables 'wrong' memory access too
> easily.
>
> (As an aside, if we really wanted to 'strictly' enforce privateness in
> this patch, shouldn't we move the "#define private" into the .c file,
> the way dir_iterator_int is in the .c file?)
That #define is pretty ugly
Another common scheme is to have an opaque pointer to the private struct
in the public struct (aka pimpl idiom). The merge machinery uses this
- see merge-recursive.h. (I'm working on something similar for the
sequencer so we can change the internals without having to re-compile
everything that includes "sequencer.h")
> - Prefixing private members with "__" (khash.h and other header-only
> libraries use this at least, not sure if we have this in the 'main
> tree'). I think this works pretty well most of the time.
It is common but I think the C standard reserves names beginning with "__"
> - Just marking private members with a comment. IMO this is good enough
> the vast majority of the time - if something is private for a good
> reason, it's unlikely to get used accidentally anyway. But properly
> enforcing "privateness" is worthy goal anyway.
>
> Personally, I think a decent tradeoff between enforcement and ergonomics
> would be to use an inner struct like you do here, but name it something
> autocomplete-friendly and obviously private, like "private" or
> "_private".
I agree, something like that would match the unpack_trees example
> I suspect self-regulation and code review should be enough
> to catch nearly all accidental uses of private members.
Agreed
Best Wishes
Phillip
next prev parent reply other threads:[~2023-08-08 19:46 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-05 5:04 [PATCH 0/5] Trailer readability cleanups Linus Arver via GitGitGadget
2023-08-05 5:04 ` [PATCH 1/5] trailer: separate public from internal portion of trailer_iterator Linus Arver via GitGitGadget
2023-08-07 21:16 ` Glen Choo
2023-08-08 12:19 ` Phillip Wood [this message]
2023-08-10 23:15 ` Linus Arver
2023-08-10 22:50 ` Linus Arver
2023-08-05 5:04 ` [PATCH 2/5] trailer: split process_input_file into separate pieces Linus Arver via GitGitGadget
2023-08-07 22:39 ` Glen Choo
2023-08-11 0:41 ` Linus Arver
2023-08-05 5:04 ` [PATCH 3/5] trailer: split process_command_line_args into separate functions Linus Arver via GitGitGadget
2023-08-07 22:51 ` Glen Choo
2023-08-11 0:59 ` Linus Arver
2023-08-11 1:02 ` Linus Arver
2023-08-11 21:11 ` Glen Choo
2023-08-05 5:04 ` [PATCH 4/5] trailer: teach find_patch_start about --no-divider Linus Arver via GitGitGadget
2023-08-07 23:28 ` Glen Choo
2023-08-11 1:25 ` Linus Arver
2023-08-11 20:51 ` Glen Choo
2023-08-05 5:04 ` [PATCH 5/5] trailer: rename *_DEFAULT enums to *_UNSPECIFIED Linus Arver via GitGitGadget
2023-08-07 23:45 ` Glen Choo
2023-08-11 18:00 ` Linus Arver
2023-09-09 6:16 ` [PATCH v2 0/6] Trailer readability cleanups Linus Arver via GitGitGadget
2023-09-09 6:16 ` [PATCH v2 1/6] trailer: separate public from internal portion of trailer_iterator Linus Arver via GitGitGadget
2023-09-11 17:10 ` Junio C Hamano
2023-09-09 6:16 ` [PATCH v2 2/6] trailer: split process_input_file into separate pieces Linus Arver via GitGitGadget
2023-09-11 17:10 ` Junio C Hamano
2023-09-09 6:16 ` [PATCH v2 3/6] trailer: split process_command_line_args into separate functions Linus Arver via GitGitGadget
2023-09-09 6:16 ` [PATCH v2 4/6] trailer: teach find_patch_start about --no-divider Linus Arver via GitGitGadget
2023-09-11 17:25 ` Junio C Hamano
2023-09-14 2:19 ` Linus Arver
2023-09-14 3:12 ` Junio C Hamano
2023-09-14 5:31 ` Linus Arver
2023-09-09 6:16 ` [PATCH v2 5/6] trailer: rename *_DEFAULT enums to *_UNSPECIFIED Linus Arver via GitGitGadget
2023-09-11 18:54 ` Junio C Hamano
2023-09-14 2:41 ` Linus Arver
2023-09-14 3:16 ` Junio C Hamano
2023-09-22 18:23 ` Linus Arver
2023-09-22 19:48 ` Junio C Hamano
2023-09-26 5:30 ` Linus Arver
2023-09-09 6:16 ` [PATCH v2 6/6] trailer: use offsets for trailer_start/trailer_end Linus Arver via GitGitGadget
2023-09-11 19:01 ` Junio C Hamano
2023-09-14 1:21 ` Linus Arver
2023-09-14 3:18 ` Linus Arver
2023-09-22 19:50 ` [PATCH v3 0/9] Trailer readability cleanups Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 1/9] trailer: separate public from internal portion of trailer_iterator Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 2/9] trailer: split process_input_file into separate pieces Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 3/9] trailer: split process_command_line_args into separate functions Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 4/9] trailer: rename *_DEFAULT enums to *_UNSPECIFIED Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 5/9] commit: ignore_non_trailer computes number of bytes to ignore Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 6/9] trailer: find the end of the log message Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 7/9] trailer: use offsets for trailer_start/trailer_end Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 8/9] trailer: only use trailer_block_* variables if trailers were found Linus Arver via GitGitGadget
2023-09-22 19:50 ` [PATCH v3 9/9] trailer: make stack variable names match field names Linus Arver via GitGitGadget
2023-09-22 22:47 ` [PATCH v3 0/9] Trailer readability cleanups Junio C Hamano
2023-09-22 23:13 ` Linus Arver
2023-09-23 0:48 ` Junio C Hamano
2023-09-26 5:40 ` Linus Arver
2023-09-26 6:22 ` [PATCH v4 0/4] " Linus Arver via GitGitGadget
2023-09-26 6:22 ` [PATCH v4 1/4] commit: ignore_non_trailer computes number of bytes to ignore Linus Arver via GitGitGadget
2023-09-26 6:22 ` [PATCH v4 2/4] trailer: find the end of the log message Linus Arver via GitGitGadget
2023-09-28 23:16 ` Jonathan Tan
2023-10-20 0:24 ` Linus Arver
2023-10-20 0:36 ` Junio C Hamano
2023-09-26 6:22 ` [PATCH v4 3/4] trailer: use offsets for trailer_start/trailer_end Linus Arver via GitGitGadget
2023-09-26 6:22 ` [PATCH v4 4/4] trailer: only use trailer_block_* variables if trailers were found Linus Arver via GitGitGadget
2023-10-20 19:01 ` [PATCH v5 0/3] Trailer readability cleanups Linus Arver via GitGitGadget
2023-10-20 19:01 ` [PATCH v5 1/3] commit: ignore_non_trailer computes number of bytes to ignore Linus Arver via GitGitGadget
2023-10-20 19:01 ` [PATCH v5 2/3] trailer: find the end of the log message Linus Arver via GitGitGadget
2023-10-20 21:29 ` Junio C Hamano
2023-12-29 6:42 ` Linus Arver
2023-12-29 21:03 ` Linus Arver
2023-10-20 19:01 ` [PATCH v5 3/3] trailer: use offsets for trailer_start/trailer_end Linus Arver via GitGitGadget
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