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From: "Martin Ågren" <martin.agren@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Git Mailing List <git@vger.kernel.org>,
	Emily Shaffer <emilyshaffer@google.com>,
	Jeff King <peff@peff.net>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>
Subject: Re: [PATCH v2 3/4] grep: copy struct in one fell swoop
Date: Wed, 25 Nov 2020 07:25:07 +0100
Message-ID: <CAN0heSoM+qQe8BdKHVpqhA0RAqzyyL3Qr98G=O8kD504diruCg@mail.gmail.com> (raw)
In-Reply-To: <xmqqsg8ygza7.fsf@gitster.c.googlers.com>

On Tue, 24 Nov 2020 at 23:34, Junio C Hamano <gitster@pobox.com> wrote:
>
> Martin Ågren <martin.agren@gmail.com> writes:
>
> > We don't have any ownership issues with what we're copying now and can
> > just greedily copy the whole thing. If and when we do need to handle
> > such elements (`char *`?), we must and can handle it appropriately.
>
> That is correct, but ...
>
> > This
> > commit doesn't really change that.
>
> ... I suspect this is not.
>
> In the original code, those who are adding a new field would notice
> that it is not copied over to the new instance (because they didn't
> add anything to grep_init() to copy the field) and at that point
> they must stop and think how the new field need to be copied.
>
> The structure assignment of the outer shell done in this patch means
> they are robbed of the opportunity to stop and think, because most
> of the time it "works" out of the box.  I'd feel safer if we left a
> clue to future developers if we were to do your clean-up, perhaps
> like:
>
> diff --git c/grep.h w/grep.h
> index b5c4e223a8..388d226da3 100644
> --- c/grep.h
> +++ w/grep.h
> @@ -115,6 +115,14 @@ struct grep_expr {
>         } u;
>  };
>
> +/*
> + * grep_config() initializes one "default" instance of this type, and
> + * it is copied by grep_init() to be used by each individual
> + * invocation.  When adding a new field to this structure that is
> + * populated from the configuration, be sure to think about ownership
> + * (i.e. a shallow copy may not be what you want for the type of your
> + * newly added field).
> + */
>  struct grep_opt {
>         struct grep_pat *pattern_list;
>         struct grep_pat **pattern_tail;

Ok, that makes sense. Maybe put it in `grep_config()` though? We can add
anything we want to to this struct and initialize it from the command
line. It's when we start pre-filling it in `grep_config()` that we need
to think about this. What do you think? We could also do both of
course to really hedge our bets...

  /*
   * The instance of grep_opt that we set up here is copied by
   * grep_init() to be used by each individual invocation.
   * When populating a new field of this structure here,
   * be sure to think about ownership (i.e. a shallow copy in
   * grep_init() may not be what you want).
   */

Thanks
Martin

  reply	other threads:[~2020-11-25  6:27 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-21 18:31 [PATCH 0/4] grep: retire `init_grep_defaults()` Martin Ågren
2020-11-21 18:31 ` [PATCH 1/4] grep: don't set up a "default" repo for grep Martin Ågren
2020-11-21 18:31 ` [PATCH 2/4] grep: use designated initializers for `grep_defaults` Martin Ågren
2020-11-21 18:31 ` [PATCH 3/4] grep: simplify color setup Martin Ågren
2020-11-21 20:23   ` Jeff King
2020-11-21 20:52     ` Martin Ågren
2020-11-21 22:46     ` Junio C Hamano
2020-11-24  6:54       ` Jeff King
2020-11-21 18:31 ` [PATCH 4/4] MyFirstObjectWalk: drop `init_walken_defaults()` Martin Ågren
2020-11-23 11:03 ` [PATCH 0/4] grep: retire `init_grep_defaults()` Johannes Schindelin
2020-11-24 21:04 ` [PATCH v2 0/4] grep: simplify "grep defaults" handling Martin Ågren
2020-11-24 21:04   ` [PATCH v2 1/4] grep: don't set up a "default" repo for grep Martin Ågren
2020-11-24 21:04   ` [PATCH v2 2/4] grep: use designated initializers for `grep_defaults` Martin Ågren
2020-11-24 21:04   ` [PATCH v2 3/4] grep: copy struct in one fell swoop Martin Ågren
2020-11-24 22:34     ` Junio C Hamano
2020-11-25  6:25       ` Martin Ågren [this message]
2020-11-25  7:53         ` Junio C Hamano
2020-11-26 20:25           ` Martin Ågren
2020-11-24 21:04   ` [PATCH v2 4/4] MyFirstObjectWalk: drop `init_walken_defaults()` Martin Ågren
2020-11-25  9:27   ` [PATCH v2 0/4] grep: simplify "grep defaults" handling Ævar Arnfjörð Bjarmason
2020-11-29 19:52   ` [PATCH v3 " Martin Ågren
2020-11-29 19:52     ` [PATCH v3 1/4] grep: don't set up a "default" repo for grep Martin Ågren
2020-11-29 19:52     ` [PATCH v3 2/4] grep: use designated initializers for `grep_defaults` Martin Ågren
2020-11-29 19:52     ` [PATCH v3 3/4] grep: copy struct in one fell swoop Martin Ågren
2020-11-29 19:52     ` [PATCH v3 4/4] MyFirstObjectWalk: drop `init_walken_defaults()` Martin Ågren
2020-12-01  4:46     ` [PATCH v3 0/4] grep: simplify "grep defaults" handling Junio C Hamano

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