[committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>>
François Dumont
frs.dumont@gmail.com
Wed Oct 6 17:18:36 GMT 2021
Here is another proposal with the __to_address overload.
I preferred to let it open to any kind of __normal_iterator
instantiation cause afaics std::vector supports fancy pointer types. It
is better if __to_address works fine also in this case, no ?
libstdc++: Overload std::__to_address for __gnu_cxx::__normal_iterator.
Prefer to overload __to_address to partially specialize
std::pointer_traits because
std::pointer_traits would be mostly useless. In the case of
__gnu_debug::_Safe_iterator
the to_pointer method is even impossible to implement correctly
because we are missing
the parent container to associate the iterator to.
libstdc++-v3/ChangeLog:
* include/bits/stl_iterator.h
(std::pointer_traits<__gnu_cxx::__normal_iterator<>>): Remove.
(std::__to_address(const __gnu_cxx::__normal_iterator<>&)):
New.
* include/debug/safe_iterator.h
(std::__to_address(const
__gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<>, _Sequence>&)):
New.
* testsuite/24_iterators/normal_iterator/to_address.cc: Add
check on std::vector::iterator
to validate both __gnu_cxx::__normal_iterator<>
__to_address overload in normal mode and the
Tested under Linux x86_64.
Ok to commit ?
François
On 04/10/21 10:30 pm, Jonathan Wakely wrote:
> On Mon, 4 Oct 2021 at 21:28, François Dumont via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
>> On 04/10/21 10:05 pm, François Dumont wrote:
>>> On 02/10/21 10:24 pm, Jonathan Wakely wrote:
>>>> On Sat, 2 Oct 2021 at 18:27, François Dumont wrote:
>>>>> I would like to propose this alternative approach.
>>>>>
>>>>> In this patch I make __normal_iterator and random iterator
>>>>> _Safe_iterator compatible for pointer_traits primary template.
>>>>>
>>>>> Regarding pointer_traits I wonder if it shouldn't check for the
>>>>> to_pointer method availability and use per default: return {
>>>>> std::addressof(__e) }; otherwise. This way we wouldn't have to
>>>>> provide a
>>>>> pointer_to method on __normal_iterator.
>>>> But I would rather not have these members present in vector::iterator
>>>> and string::iterator, in case users accidentally start to rely on them
>>>> being present.
>>> Making pointer_traits friends would help but I do not like it neither.
>>>
>>>
>>>> Another option would be to overload std::__to_address so it knows how
>>>> to get the address from __normal_iterator and _Safe_iterator.
>>>>
>>>> .
>>> I start thinking that rather than proposing not-useful and even
>>> incorrect code in the case of the _Safe_iterator<> it might be a
>>> better approach.
>>>
>>> Even the rebind for __normal_iterator is a little strange because when
>>> doing rebind on std::vector<int>::iterator for long it produces
>>> __normal_iterator<long*, std::vector<int>>, quite inconsistent even if
>>> useless.
>>>
>>>
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