From: "François Dumont" <frs.dumont@gmail.com>
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: Jonathan Wakely <jwakely@redhat.com>,
libstdc++ <libstdc++@gcc.gnu.org>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>>
Date: Wed, 6 Oct 2021 19:18:36 +0200 [thread overview]
Message-ID: <193032c8-8b9a-3e55-a244-075b0031d758@gmail.com> (raw)
In-Reply-To: <CAH6eHdTFjVv=q10Qe4Y+LOnOmcOTqeCBFROjaOpXWKN4dH8xKQ@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2999 bytes --]
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.
>>>
>>>
[-- Attachment #2: to_address.patch --]
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diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 8afd6756613..6b915ec011c 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1312,32 +1312,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus >= 201103L
- // Need to specialize pointer_traits because the primary template will
- // deduce element_type of __normal_iterator<T*, C> as T* rather than T.
+ // Need to overload __to_address because the pointer_traits primary template
+ // will deduce element_type of __normal_iterator<T*, C> as T* rather than T.
template<typename _Iterator, typename _Container>
- struct pointer_traits<__gnu_cxx::__normal_iterator<_Iterator, _Container>>
- {
- private:
- using _Base = pointer_traits<_Iterator>;
-
- public:
- using element_type = typename _Base::element_type;
- using pointer = __gnu_cxx::__normal_iterator<_Iterator, _Container>;
- using difference_type = typename _Base::difference_type;
-
- template<typename _Tp>
- using rebind = __gnu_cxx::__normal_iterator<_Tp, _Container>;
-
- static pointer
- pointer_to(element_type& __e) noexcept
- { return pointer(_Base::pointer_to(__e)); }
-
-#if __cplusplus >= 202002L
- static element_type*
- to_address(pointer __p) noexcept
- { return __p.base(); }
-#endif
- };
+ constexpr auto
+ __to_address(const __gnu_cxx::__normal_iterator<_Iterator,
+ _Container>& __it) noexcept
+ -> decltype(std::__to_address(__it.base()))
+ { return std::__to_address(__it.base()); }
/**
* @addtogroup iterators
diff --git a/libstdc++-v3/include/debug/safe_iterator.h b/libstdc++-v3/include/debug/safe_iterator.h
index 5584d06de5a..09e35f79067 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -1018,6 +1018,23 @@ namespace __gnu_debug
#undef _GLIBCXX_DEBUG_VERIFY_EQ_OPERANDS
#undef _GLIBCXX_DEBUG_VERIFY_OPERANDS
+#if __cplusplus >= 201103L
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+ template<typename _Iterator, typename _Container, typename _Sequence>
+ constexpr auto
+ __to_address(const __gnu_debug::_Safe_iterator<
+ __gnu_cxx::__normal_iterator<_Iterator, _Container>,
+ _Sequence>& __it) noexcept
+ -> decltype(std::__to_address(__it.base()))
+ { return std::__to_address(__it.base()); }
+
+_GLIBCXX_END_NAMESPACE_VERSION
+}
+#endif
+
#include <debug/safe_iterator.tcc>
#endif
diff --git a/libstdc++-v3/testsuite/24_iterators/normal_iterator/to_address.cc b/libstdc++-v3/testsuite/24_iterators/normal_iterator/to_address.cc
index 510d627435f..433c803beb1 100644
--- a/libstdc++-v3/testsuite/24_iterators/normal_iterator/to_address.cc
+++ b/libstdc++-v3/testsuite/24_iterators/normal_iterator/to_address.cc
@@ -1,6 +1,9 @@
// { dg-do compile { target { c++11 } } }
#include <string>
+#include <vector>
#include <memory>
char* p = std::__to_address(std::string("1").begin());
const char* q = std::__to_address(std::string("2").cbegin());
+int* r = std::__to_address(std::vector<int>(1, 1).begin());
+const int* s = std::__to_address(std::vector<int>(1, 1).cbegin());
next prev parent reply other threads:[~2021-10-06 17:18 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-28 19:25 Jonathan Wakely
2021-09-30 20:24 ` François Dumont
2021-10-01 22:29 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-02 13:08 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-10-02 20:28 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-02 17:27 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-10-02 20:24 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-04 20:05 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-10-04 20:26 ` François Dumont
2021-10-04 20:30 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-06 17:18 ` François Dumont [this message]
2021-10-06 17:25 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-12-14 6:53 ` François Dumont
2021-12-14 13:12 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-12-15 21:16 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-12-15 21:21 ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
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