From: "René Scharfe" <l.s.r@web.de>
To: Junio C Hamano <gitster@pobox.com>
Cc: Git List <git@vger.kernel.org>
Subject: Re: [PATCH 1/3] do full type check in COPY_ARRAY and MOVE_ARRAY
Date: Sun, 1 Jan 2023 11:45:41 +0100 [thread overview]
Message-ID: <bf4e6798-c687-270d-1344-37bacb403e13@web.de> (raw)
In-Reply-To: <220515b3-3924-c8d2-ff20-7017caa7dead@web.de>
Am 01.01.23 um 08:41 schrieb René Scharfe:
> Am 01.01.23 um 04:59 schrieb Junio C Hamano:
>> Junio C Hamano <gitster@pobox.com> writes:
>>
>>> ... I think what you ideally want to enforce is that
>>> typeof(dst) is exactly typeof(src), or typeof(src) sans constness
>>> (i.e. you can populate non-const array from a const template)?
>
> Yes.
>
> Moving the type check shared between COPY_ARRAY and MOVE_ARRAY to a new
> macro is a good idea.
>
> Using compiler extensions when available, as we already do for other
> purposes, is a good idea as well. I managed to ignore the existing use
> somehow.
On second thought, what do we gain by using __builtin_types_compatible_p
here? Does it catch cases that the assignment check plus the element
size check wouldn't?
>
>>
>> IOW, I am wondering if something like this is an improvement.
>>
>> git-compat-util.h | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git c/git-compat-util.h w/git-compat-util.h
>> index a76d0526f7..be435615f0 100644
>> --- c/git-compat-util.h
>> +++ w/git-compat-util.h
>> @@ -97,8 +97,13 @@ struct strbuf;
>> # define BARF_UNLESS_AN_ARRAY(arr) \
>> BUILD_ASSERT_OR_ZERO(!__builtin_types_compatible_p(__typeof__(arr), \
>> __typeof__(&(arr)[0])))
>> +# define ARRAYS_COPYABLE_OR_ZERO(src,dst) \
>> + (BUILD_ASSERT_OR_ZERO(!__builtin_types_compatible_p(__typeof__(src), \
>> + __typeof__(dst))) + \
We actually need to compare the types of the elements here, because
otherwise we'd disallow copies between arrays (int arr[7]) and pointers
(int *p), which would be unnecessarily strict.
>> + (0 ? *(dst) = *(src) : 0))
You dropped the ", 0" after the assignment, but we need it to make the
type of this expression int instead of whatever type *dst and *src have.
>> #else
>> # define BARF_UNLESS_AN_ARRAY(arr) 0
>> +# define ARRAYS_COPYABLE_OR_ZERO(src,dst) (0 ? *(dst) = *(src) : 0))
>> #endif
>> /*
>> * ARRAY_SIZE - get the number of elements in a visible array
next prev parent reply other threads:[~2023-01-01 10:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-30 21:51 [PATCH 0/3] COPY_ARRAY, MOVE_ARRAY, DUP_ARRAY René Scharfe
2022-12-30 21:56 ` [PATCH 1/3] do full type check in COPY_ARRAY and MOVE_ARRAY René Scharfe
2023-01-01 3:03 ` Junio C Hamano
2023-01-01 3:59 ` Junio C Hamano
2023-01-01 7:41 ` René Scharfe
2023-01-01 10:45 ` René Scharfe [this message]
2023-01-01 12:11 ` Junio C Hamano
2023-01-01 12:32 ` René Scharfe
2023-01-01 12:46 ` Junio C Hamano
2022-12-30 22:02 ` [PATCH 2/3] add DUP_ARRAY René Scharfe
2022-12-30 22:03 ` [PATCH 3/3] use DUP_ARRAY René Scharfe
2023-01-01 21:05 ` [PATCH v2 0/4] COPY_ARRAY, MOVE_ARRAY, DUP_ARRAY René Scharfe
2023-01-01 21:08 ` [PATCH v2 1/4] factor out BARF_UNLESS_COPYABLE René Scharfe
2023-01-01 21:11 ` [PATCH v2 2/4] do full type check in BARF_UNLESS_COPYABLE René Scharfe
2023-01-08 7:28 ` Junio C Hamano
2023-01-08 10:10 ` René Scharfe
2023-01-09 4:27 ` Junio C Hamano
2023-01-09 18:08 ` Jeff Hostetler
2023-01-01 21:14 ` [PATCH v2 3/4] add DUP_ARRAY René Scharfe
2023-01-01 21:16 ` [PATCH v2 4/4] use DUP_ARRAY René Scharfe
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