On 19/04/21 22:25 -0400, Patrick Palka via Libstdc++ wrote:
This implements the wording changes of P2259R1 "Repairing input range adaptors and counted_iterator", which resolves LWG 3283, 3289 and 3408.The wording changes are relatively straightforward, but they require some boilerplate to implement: the changes to make a type alias "conditionally present" in some iterator class are realized by defining a base class template and an appropriately constrained partial specialization thereof that contains the type alias, and having the iterator class derive from this base class. Sometimes the relevant condition depend on members from the iterator class, but because a class is incomplete when instantiating its bases, the constraints on the partial specialization can't use anything from the iterator class. This patch works around this by hoisting these members out to the enclosing scope (e.g. transform_view::_Iterator::_Base is hoisted out to transform_view::_Base so that transform_view::__iter_cat can use it). This patch also implements the proposed resolution of LWG 3291 to rename iota_view::iterator_category to iota_view::iterator_concept, which was previously problematic due to LWG 3408. Tested on x86_64-pc-linux-gnu. libstdc++-v3/ChangeLog: PR libstdc++/95983 * include/bits/stl_iterator.h (__detail::__move_iter_cat): Define. (move_iterator): Derive from the above in C++20 in order to conditionally define iterator_category as per P2259. (move_iterator::__base_cat): No longer used, so remove. (move_iterator::iterator_category): Remove in C++20. (__detail::__common_iter_use_postfix_proxy): Define. (common_iterator::_Proxy): Rename to ... (common_iterator:__arrow_proxy): ... this. (common_iterator::__postfix_proxy): Define as per P2259. (common_iterator::operator->): Adjust. (common_iterator::operator++): Adjust as per P2259. (iterator_traits<common_iterator>::_S_iter_cat): Define. (iterator_traits<common_iterator>::iterator_category): Change as per P2259. (__detail::__counted_iter_value_type): Define. (__detail::__counted_iter_concept): Define. (__detail::__counted_iter_cat): Define. (counted_iterator): Derive from the above three classes in order to conditionally define value_type, iterator_concept and iterator category respectively as per P2259. (counted_iterator::operator->): Define as per P2259. (incrementable_traits<counted_iterator>): Remove as per P2259. (iterator_traits<counted_iterator>): Adjust as per P2259. * include/std/ranges (__detail::__iota_view_iter_cat): Define. (iota_view::_Iterator): Derive from the above in order to conditionally define iterator_category as per P2259. (iota_view::_S_iter_cat): Rename to ... (iota_view::_S_iter_concept): ... this. (iota_view::iterator_concept): Use it to apply LWG 3291 changes. (iota_view::iterator_category): Remove. (__detail::__filter_view_iter_cat): Define. (filter_view::_Iterator): Derive from the above in order to conditionally define iterator_category as per P2259. (filter_view::_Iterator): Move to struct __filter_view_iter_cat. (filter_view::_Iterator::iterator_category): Remove. (transform_view::_Base): Define. (transform_view::__iter_cat): Define. (transform_view::_Iterator): Derive from the above in order to conditionally define iterator_category as per P2259. (transform_view::_Iterator::_Base): Just alias transform_view::_Base. (transform_view::_Iterator::_S_iter_cat): Move to struct transform_view::__iter_cat. (transform_view::_Iterator::iterator_category): Remove. (transform_view::_Sentinel::_Base): Just alias transform_view::_Base. (join_view::_Base): Define. (join_view::_Outer_iter): Define. (join_view::_Inner_iter): Define. (join_view::_S_ref_is_glvalue): Define. (join_view::__iter_cat): Define. (join_view::_Iterator): Derive from it in order to conditionally define iterator_category as per P2259. (join_view::_Iterator::_Base): Just alias join_view::_Base. (join_view::_Iterator::_S_ref_is_glvalue): Just alias join_view::_S_ref_is_glvalue. (join_view::_Iterator::_S_iter_cat): Move to struct transform_view::__iter_cat. (join_view::_Iterator::_Outer_iter): Just alias join_view::_Outer_iter. (join_view::_Iterator::_Inner_iter): Just alias join_view::_Inner_iter. (join_view::_Iterator::iterator_category): Remove. (join_view::_Sentinel::_Base): Just alias join_view::_Base. (__detail::__split_view_outer_iter_cat): Define. (__detail::__split_view_inner_iter_cat): Define. (split_view::_Base): Define. (split_view::_Outer_iter): Derive from __split_view_outer_iter_cat in order to conditionally define iterator_category as per P2259. (split_view::_Outer_iter::iterator_category): Remove. (split_view::_Inner_iter): Derive from __split_view_inner_iter_cat in order to conditionally define iterator_category as per P2259. (split_view::_Inner_iter::_S_iter_cat): Move to __split_view_inner_iter_cat. (split_view::_Inner_iter::iterator_category): Remove. (elements_view::_Base): Define. (elements_view::__iter_cat): Define. (elements_view::_Iterator): Derive from the above in order to conditionall define iterator_category as per P2259. (elements_view::_Iterator::_Base): Just alias elements_view::_Base. (elements_view::_Iterator::_S_iter_concept) (elements_view::_Iterator::iterator_concept): Define as per P2259. (elements_view::_Iterator::iterator_category): Remove. (elements_view::_Sentinel::_Base): Just alias elements_view::_Base. * testsuite/24_iterators/headers/iterator/synopsis_c++20: Adjust constraints on iterator_traits<counted_iterator>. * testsuite/std/ranges/p2259.cc: New test. --- libstdc++-v3/include/bits/stl_iterator.h | 128 ++++++-- libstdc++-v3/include/std/ranges | 299 ++++++++++++------ .../headers/iterator/synopsis_c++20.cc | 1 + libstdc++-v3/testsuite/std/ranges/p2259.cc | 91 ++++++ 4 files changed, 412 insertions(+), 107 deletions(-) create mode 100644 libstdc++-v3/testsuite/std/ranges/p2259.cc diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index dc8b101e8f8..049f83cff90 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -1302,6 +1302,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION }; #endif // C++20 + namespace __detail + { +#if __cplusplus > 201703L && __cpp_lib_concepts + template<typename _Iterator> + struct __move_iter_cat + { }; + + template<typename _Iterator> + requires requires { typename iterator_traits<_Iterator>::iterator_category; } + struct __move_iter_cat<_Iterator> + { + using iterator_category + = __clamp_iter_cat<typename iterator_traits<_Iterator>::iterator_category, + random_access_iterator_tag>; + }; +#endif + } + // 24.4.3 Move iterators /** * Class template move_iterator is an iterator adapter with the same @@ -1313,13 +1331,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION */ template<typename _Iterator> class move_iterator +#if __cplusplus > 201703L && __cpp_lib_concepts + : public __detail::__move_iter_cat<_Iterator> +#endif { _Iterator _M_current; using __traits_type = iterator_traits<_Iterator>; -#if __cplusplus > 201703L && __cpp_lib_concepts - using __base_cat = typename __traits_type::iterator_category; -#else +#if ! (__cplusplus > 201703L && __cpp_lib_concepts)
These preprocessor conditionals would be simpler if we just used __cpp_lib_concepts instead of (C++20 && __cpp_lib_concepts). That would be fine, because __cpp_lib_concepts is only defined for C++20 anyway. But we can change that later, not as part of this patch.
using __base_ref = typename __traits_type::reference; #endif
OK for trunk and gcc-11 branch, thanks. We should also look into whether backporting to gcc-10 is feasible. I think it should be, but I didn't try.
