Re: [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>>

["François Dumont" <frs.dumont@gmail.com>]

Hi

     Any conclusion regarding this thread ?

François


On 06/10/21 7:25 pm, François Dumont wrote:
> I forgot to ask if with this patch this overload:
>
>   template<typename _Ptr, typename... _None>
>     constexpr auto
>     __to_address(const _Ptr& __ptr, _None...) noexcept
>     {
>       if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
>     return std::__to_address(__ptr.base().operator->());
>       else
>     return std::__to_address(__ptr.operator->());
>     }
>
> should be removed ?
>
> Or perhaps just the _Safe_iterator_base branch in it ?
>
> On 06/10/21 7:18 pm, François Dumont wrote:
>> 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.
>>>>>
>>>>>
>