[cfe-dev] [libc++] Potential bug in debug/array

[Eric Fiselier via cfe-dev]

Looks like libstdc++ fixed this 3 years ago: https://gcc.gnu.org/r224153

/Eric

On Fri, May 18, 2018 at 3:01 AM, Liu Hao via cfe-dev <cfe-dev at lists.llvm.org
> wrote:

> 在 2018/5/18 0:09, Lucas Czech via cfe-dev 写道:
>
>> Error message:
>>
>> |/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../../include/c++/4.9/debug/array:86:52:
>>
>>
>
> This is a libstdc++ header, so it cannot be a libc++ bug.
>
> It is however a clang bug. See below.
>
> The issue was discussed here: https://github.com/greg7mdp/sp
>> arsepp/issues/61
>> where greg7mdp <https://github.com/greg7mdp> suggested that the problem
>> might be a missing `std` in front of the swap() call:
>>
>>
> It might resolve the issue but is not a correct solution.
>
> |void swap(array& __other) noexcept(noexcept(_*std::*_swap(std::declval<_Tp&>(),
>> std::declval<_Tp&>()))) { std::swap_ranges(begin(), end(),
>> __other.begin()); }|
>>
>>
>>
> The second, unqualified `swap` is envisioned to involve the Argument
> Dependent Lookup (ADL) and call whatever ADL finds, and if ADL fails to
> find (a most probably user-defined) one, call the one in `std`.
>
> Here clang behaves as if the second `swap` is hidden by the first one
> being declared. This is the bug, because the exception specification is
> part of the function declarator and is before the point of declaration of
> the function being declared, and consequently, shall not make the name of
> the function in question visible.
>
> The use of the qualified name `std::swap` prevents the second `swap` from
> being hidden as described above, but it also forbids ADL so user-defined
> `swap` functions cannot be found at all. This is a minor issue if you have
> had move assignment operators implemented properly, nevertheless.
>
>
> Please let me know if this is a bug in libc++, or an issue with sparsepp,
>> where the problem manifests.
>>
>> Thanks
>> Lucas
>>
>>
>
>
> --
> Best regards,
> LH_Mouse
>
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