From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2136) id DD2623A15804; Wed, 17 Jun 2020 20:01:00 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org DD2623A15804 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1592424060; bh=QPVXRzKnmYpFWYHSL+okrsmDk1ol/WpGlYDx7AtoXs8=; h=From:To:Subject:Date:From; b=thmdTO8y1nr+lngSxRFOg6nl9igA+8H/1S55tGRz1oIyeTZVtU/nezkkZC+ks0R+D 4YRlAzdb3Wis9JYUL3JMnMeMkY3cKWBI5qq2pl0FxijuXtgE1pqmEb8fWQvJoFtCs+ ryVktLLN7Hn1A87QqhFVg/ZkvRQdxN+Is8DKXi70= Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: Aldy Hernandez To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc/devel/ranger] libstdc++: Add remaining C++20 changes to iterator adaptors X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/devel/ranger X-Git-Oldrev: ae6076b5bc1e0b689eaa8521571b0516de336553 X-Git-Newrev: 81a8d137c22953df2ea046466c62cd26c0dba103 Message-Id: <20200617200100.DD2623A15804@sourceware.org> Date: Wed, 17 Jun 2020 20:01:00 +0000 (GMT) X-BeenThere: libstdc++-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 17 Jun 2020 20:01:01 -0000 https://gcc.gnu.org/g:81a8d137c22953df2ea046466c62cd26c0dba103 commit 81a8d137c22953df2ea046466c62cd26c0dba103 Author: Jonathan Wakely Date: Fri Mar 27 23:21:58 2020 +0000 libstdc++: Add remaining C++20 changes to iterator adaptors This adds the missing parts of P0896R4 to reverse_iterator and move_iterator, so that they meet the C++20 requirements. This should be the last piece of P0896R4, meaning ranges support is now complete. The PR 94354 bug with reverse_iterator's comparisons is fixed for C++20 only, but that change should be extended to C++11, C++14 and C++17 modes in stage 1. * include/bits/stl_iterator.h (reverse_iterator::iterator_concept) (reverse_iterator::iterator_category): Define for C++20. (reverse_iterator): Define comparison operators correctly for C++20. (__normal_iterator): Add constraints to comparison operators for C++20. (move_iterator::operator++(int)) [__cpp_lib_concepts]: Define new overload for input iterators. (move_iterator): Add constraints to comparison operators for C++20. Define operator<=> for C++20. * testsuite/24_iterators/move_iterator/input_iterator.cc: New test. * testsuite/24_iterators/move_iterator/move_only.cc: New test. * testsuite/24_iterators/move_iterator/rel_ops_c++20.cc: New test. * testsuite/24_iterators/reverse_iterator/rel_ops_c++20.cc: New test. Diff: --- libstdc++-v3/ChangeLog | 13 ++ libstdc++-v3/include/bits/stl_iterator.h | 131 +++++++++++++++-- .../24_iterators/move_iterator/input_iterator.cc | 42 ++++++ .../24_iterators/move_iterator/move_only.cc | 60 ++++++++ .../24_iterators/move_iterator/rel_ops_c++20.cc | 134 ++++++++++++++++++ .../24_iterators/reverse_iterator/rel_ops_c++20.cc | 156 +++++++++++++++++++++ 6 files changed, 521 insertions(+), 15 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index c529206a4b9..fc5f900ed5f 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,5 +1,18 @@ 2020-03-27 Jonathan Wakely + * include/bits/stl_iterator.h (reverse_iterator::iterator_concept) + (reverse_iterator::iterator_category): Define for C++20. + (reverse_iterator): Define comparison operators correctly for C++20. + (__normal_iterator): Add constraints to comparison operators for C++20. + (move_iterator::operator++(int)) [__cpp_lib_concepts]: Define new + overload for input iterators. + (move_iterator): Add constraints to comparison operators for C++20. + Define operator<=> for C++20. + * testsuite/24_iterators/move_iterator/input_iterator.cc: New test. + * testsuite/24_iterators/move_iterator/move_only.cc: New test. + * testsuite/24_iterators/move_iterator/rel_ops_c++20.cc: New test. + * testsuite/24_iterators/reverse_iterator/rel_ops_c++20.cc: New test. + * include/bits/iterator_concepts.h (__detail::__decay_copy) (__detail::__member_begin, __detail::__adl_begin): Move here from . diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index d10c30cbfcc..26eb599993d 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -88,6 +88,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION * @{ */ +#if __cplusplus > 201703L && __cpp_lib_concepts + namespace __detail + { + // Weaken iterator_category _Cat to _Limit if it is derived from that, + // otherwise use _Otherwise. + template + using __clamp_iter_cat + = conditional_t, _Limit, _Otherwise>; + } +#endif + // 24.4.1 Reverse iterators /** * Bidirectional and random access iterators have corresponding reverse @@ -126,6 +137,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION typedef typename __traits_type::pointer pointer; typedef typename __traits_type::reference reference; +#if __cplusplus > 201703L && __cpp_lib_concepts + using iterator_concept + = conditional_t, + random_access_iterator_tag, + bidirectional_iterator_tag>; + using iterator_category + = __detail::__clamp_iter_cat; +#endif + /** * The default constructor value-initializes member @p current. * If it is a pointer, that means it is zero-initialized. @@ -320,16 +341,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return __t.operator->(); } }; + // Used in unevaluated expressions to test for implicit conversion to bool. + namespace __detail { bool __convbool(bool); } + //@{ /** * @param __x A %reverse_iterator. * @param __y A %reverse_iterator. * @return A simple bool. * - * Reverse iterators forward many operations to their underlying base() - * iterators. Others are implemented in terms of one another. + * Reverse iterators forward comparisons to their underlying base() + * iterators. * */ +#if __cplusplus <= 201703L template inline _GLIBCXX17_CONSTEXPR bool operator==(const reverse_iterator<_Iterator>& __x, @@ -403,6 +428,49 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION operator>=(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) { return !(__x < __y); } +#else // C++20 + template + constexpr auto + operator==(const reverse_iterator<_IteratorL>& __x, + const reverse_iterator<_IteratorR>& __y) + -> decltype(__detail::__convbool(__x.base() == __y.base())) + { return __x.base() == __y.base(); } + + template + constexpr auto + operator!=(const reverse_iterator<_IteratorL>& __x, + const reverse_iterator<_IteratorR>& __y) + -> decltype(__detail::__convbool(__x.base() != __y.base())) + { return __x.base() != __y.base(); } + + template + constexpr auto + operator<(const reverse_iterator<_IteratorL>& __x, + const reverse_iterator<_IteratorR>& __y) + -> decltype(__detail::__convbool(__x.base() < __y.base())) + { return __x.base() < __y.base(); } + + template + constexpr auto + operator>(const reverse_iterator<_IteratorL>& __x, + const reverse_iterator<_IteratorR>& __y) + -> decltype(__detail::__convbool(__x.base() > __y.base())) + { return __x.base() > __y.base(); } + + template + constexpr auto + operator<=(const reverse_iterator<_IteratorL>& __x, + const reverse_iterator<_IteratorR>& __y) + -> decltype(__detail::__convbool(__x.base() <= __y.base())) + { return __x.base() <= __y.base(); } + + template + constexpr auto + operator>=(const reverse_iterator<_IteratorL>& __x, + const reverse_iterator<_IteratorR>& __y) + -> decltype(__detail::__convbool(__x.base() >= __y.base())) + { return __x.base() >= __y.base(); } +#endif // C++20 //@} #if __cplusplus < 201103L @@ -1000,8 +1068,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Random access iterator requirements template - _GLIBCXX20_CONSTEXPR +#if __cplusplus > 201703L + constexpr auto +#else inline bool +#endif operator<(const __normal_iterator<_IteratorL, _Container>& __lhs, const __normal_iterator<_IteratorR, _Container>& __rhs) _GLIBCXX_NOEXCEPT @@ -1016,8 +1087,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return __lhs.base() < __rhs.base(); } template - _GLIBCXX20_CONSTEXPR +#if __cplusplus > 201703L + constexpr auto +#else inline bool +#endif operator>(const __normal_iterator<_IteratorL, _Container>& __lhs, const __normal_iterator<_IteratorR, _Container>& __rhs) _GLIBCXX_NOEXCEPT @@ -1032,8 +1106,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return __lhs.base() > __rhs.base(); } template - _GLIBCXX20_CONSTEXPR +#if __cplusplus > 201703L + constexpr auto +#else inline bool +#endif operator<=(const __normal_iterator<_IteratorL, _Container>& __lhs, const __normal_iterator<_IteratorR, _Container>& __rhs) _GLIBCXX_NOEXCEPT @@ -1048,8 +1125,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return __lhs.base() <= __rhs.base(); } template - _GLIBCXX20_CONSTEXPR +#if __cplusplus > 201703L + constexpr auto +#else inline bool +#endif operator>=(const __normal_iterator<_IteratorL, _Container>& __lhs, const __normal_iterator<_IteratorR, _Container>& __rhs) _GLIBCXX_NOEXCEPT @@ -1157,15 +1237,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION private: _Sent _M_last; }; - - namespace __detail - { - // Weaken iterator_category _Cat to _Limit if it is derived from that, - // otherwise use _Otherwise. - template - using __clamp_iter_cat - = conditional_t, _Limit, _Otherwise>; - } #endif // C++20 // 24.4.3 Move iterators @@ -1266,6 +1337,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION return __tmp; } +#if __cpp_lib_concepts + constexpr void + operator++(int) requires (!forward_iterator<_Iterator>) + { ++_M_current; } +#endif + _GLIBCXX17_CONSTEXPR move_iterator& operator--() { @@ -1343,6 +1420,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION inline _GLIBCXX17_CONSTEXPR bool operator==(const move_iterator<_IteratorL>& __x, const move_iterator<_IteratorR>& __y) +#if __cplusplus > 201703L && __cpp_lib_concepts + requires requires { __detail::__convbool(__x.base() == __y.base()); } +#endif { return __x.base() == __y.base(); } template @@ -1351,6 +1431,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const move_iterator<_Iterator>& __y) { return __x.base() == __y.base(); } +#if __cpp_lib_three_way_comparison + template _IteratorR> + constexpr compare_three_way_result_t<_IteratorL, _IteratorR> + operator<=>(const move_iterator<_IteratorL>& __x, + const move_iterator<_IteratorR>& __y) + { return __x.base() <=> __y.base(); } +#else template inline _GLIBCXX17_CONSTEXPR bool operator!=(const move_iterator<_IteratorL>& __x, @@ -1362,11 +1450,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION operator!=(const move_iterator<_Iterator>& __x, const move_iterator<_Iterator>& __y) { return !(__x == __y); } +#endif template inline _GLIBCXX17_CONSTEXPR bool operator<(const move_iterator<_IteratorL>& __x, const move_iterator<_IteratorR>& __y) +#if __cplusplus > 201703L && __cpp_lib_concepts + requires requires { __detail::__convbool(__x.base() < __y.base()); } +#endif { return __x.base() < __y.base(); } template @@ -1379,6 +1471,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION inline _GLIBCXX17_CONSTEXPR bool operator<=(const move_iterator<_IteratorL>& __x, const move_iterator<_IteratorR>& __y) +#if __cplusplus > 201703L && __cpp_lib_concepts + requires requires { __detail::__convbool(__y.base() < __x.base()); } +#endif { return !(__y < __x); } template @@ -1391,6 +1486,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION inline _GLIBCXX17_CONSTEXPR bool operator>(const move_iterator<_IteratorL>& __x, const move_iterator<_IteratorR>& __y) +#if __cplusplus > 201703L && __cpp_lib_concepts + requires requires { __detail::__convbool(__y.base() < __x.base()); } +#endif { return __y < __x; } template @@ -1403,6 +1501,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION inline _GLIBCXX17_CONSTEXPR bool operator>=(const move_iterator<_IteratorL>& __x, const move_iterator<_IteratorR>& __y) +#if __cplusplus > 201703L && __cpp_lib_concepts + requires requires { __detail::__convbool(__x.base() < __y.base()); } +#endif { return !(__x < __y); } template diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/input_iterator.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/input_iterator.cc new file mode 100644 index 00000000000..32cf55ca932 --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/input_iterator.cc @@ -0,0 +1,42 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2a" } +// { dg-do run { target c++2a } } + +#include +#include +#include + +void +test01() +{ + int a[2] = { 1, 2 }; + __gnu_test::test_container c(a); + auto miter = std::make_move_iterator(c.begin()); + VERIFY( *miter == 1 ); + miter++; + VERIFY( *miter == 2 ); + + static_assert( std::is_void_v ); +} + +int +main() +{ + test01(); +} diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc new file mode 100644 index 00000000000..d64e61e4448 --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc @@ -0,0 +1,60 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include + +struct move_only_iterator +{ + move_only_iterator() = default; + move_only_iterator(move_only_iterator&&) = default; + move_only_iterator& operator=(move_only_iterator&&) = default; + + move_only_iterator& operator++(); + move_only_iterator operator++(int); + int& operator*() const; + + bool operator==(const move_only_iterator&) const; +}; + +template<> struct std::iterator_traits +{ + using value_type = int; + using difference_type = std::ptrdiff_t; + using iterator_category = std::input_iterator_tag; +}; + +static_assert(std::input_iterator); + +template + concept has_member_base = requires (T t) { std::forward(t).base(); }; + +static_assert( ! has_member_base&> ); +static_assert( ! has_member_base&> ); +static_assert( has_member_base> ); +static_assert( ! has_member_base> ); + +void +test01() +{ + std::move_iterator m1, m2; + m1 = std::make_move_iterator(move_only_iterator{}); + m2 = std::move(m1); + m1.swap(m2); +} diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/rel_ops_c++20.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/rel_ops_c++20.cc new file mode 100644 index 00000000000..8f2d73c520f --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/rel_ops_c++20.cc @@ -0,0 +1,134 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include + +template +struct Iter +{ + using iterator_category = std::random_access_iterator_tag; + using value_type = int; + using pointer = int*; + using reference = int&; + using difference_type = std::ptrdiff_t; + + Iter(); + + Iter& operator++(); + Iter operator++(int); + Iter& operator--(); + Iter operator--(int); + int& operator*() const; + int* operator->() const; + + int& operator[](difference_type) const; + + Iter& operator+=(difference_type); + Iter& operator-=(difference_type); + + template friend Iter operator+(Iter, difference_type); + template friend Iter operator+(difference_type, Iter); + template friend Iter operator-(Iter, difference_type); + template friend difference_type operator-(Iter, Iter); + + // Define the full set of operators for same-type comparisons + template friend bool operator==(Iter, Iter); // synthesizes != + template friend bool operator<(Iter, Iter); + template friend bool operator>(Iter, Iter); + template friend bool operator<=(Iter, Iter); + template friend bool operator>=(Iter, Iter); +}; + + +static_assert( std::random_access_iterator> ); + +int operator==(Iter<0>, long*); +void* operator< (Iter<1>, long*); +bool& operator< (long*, Iter<2>); + +using std::move_iterator; + +static_assert( std::three_way_comparable>> ); + +move_iterator> l0{Iter<0>()}; +move_iterator> l1{Iter<1>()}; +move_iterator> l2{Iter<2>()}; +move_iterator r{nullptr}; + +bool b0 = l0 == r; +bool b1 = l0 != r; +bool b2 = l1 < r; +bool b3 = l2 > r; +bool b4 = l2 <= r; +bool b5 = l1 >= r; + +template + concept has_eq + = requires (move_iterator> l, move_iterator r) + { l == r; }; + +template + concept has_ne + = requires (move_iterator> l, move_iterator r) + { l != r; }; + +template + concept has_lt + = requires (move_iterator> l, move_iterator r) + { l < r; }; + +template + concept has_gt + = requires (move_iterator> l, move_iterator r) + { l > r; }; + +template + concept has_le + = requires (move_iterator> l, move_iterator r) + { l <= r; }; + +template + concept has_ge + = requires (move_iterator> l, move_iterator r) + { l >= r; }; + +static_assert( has_eq<0> ); +static_assert( ! has_eq<1> ); +static_assert( ! has_eq<2> ); + +static_assert( has_ne<0> ); // uses synthesized operator!= +static_assert( ! has_ne<1> ); +static_assert( ! has_ne<2> ); + +static_assert( ! has_lt<0> ); +static_assert( has_lt<1> ); +static_assert( ! has_lt<2> ); + +static_assert( ! has_gt<0> ); +static_assert( ! has_gt<1> ); +static_assert( has_gt<2> ); + +static_assert( ! has_le<0> ); +static_assert( ! has_le<1> ); +static_assert( has_le<2> ); + +static_assert( ! has_ge<0> ); +static_assert( has_ge<1> ); +static_assert( ! has_ge<2> ); diff --git a/libstdc++-v3/testsuite/24_iterators/reverse_iterator/rel_ops_c++20.cc b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/rel_ops_c++20.cc new file mode 100644 index 00000000000..3e91a0396fe --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/rel_ops_c++20.cc @@ -0,0 +1,156 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include + +template +struct Iter +{ + using iterator_category = std::random_access_iterator_tag; + using value_type = int; + using pointer = int*; + using reference = int&; + using difference_type = std::ptrdiff_t; + + Iter(); + + Iter& operator++(); + Iter operator++(int); + Iter& operator--(); + Iter operator--(int); + int& operator*() const; + int* operator->() const; + + int& operator[](difference_type) const; + + Iter& operator+=(difference_type); + Iter& operator-=(difference_type); + + template friend Iter operator+(Iter, difference_type); + template friend Iter operator+(difference_type, Iter); + template friend Iter operator-(Iter, difference_type); + template friend difference_type operator-(Iter, Iter); + + // Define the full set of operators for same-type comparisons + template friend bool operator==(Iter, Iter); // synthesizes != + template friend bool operator<(Iter, Iter); + template friend bool operator>(Iter, Iter); + template friend bool operator<=(Iter, Iter); + template friend bool operator>=(Iter, Iter); +}; + +static_assert( std::random_access_iterator> ); + +// Define a single kind of mixed-type comparison for each specialization. +int operator==(Iter<0>, long*); +void* operator!=(Iter<1>, long*); +bool& operator< (Iter<2>, long*); +int operator> (Iter<3>, long*); +void* operator<=(Iter<4>, long*); +bool& operator>=(Iter<5>, long*); + +using std::reverse_iterator; + +reverse_iterator> l0{Iter<0>()}; +reverse_iterator> l1{Iter<1>()}; +reverse_iterator> l2{Iter<2>()}; +reverse_iterator> l3{Iter<3>()}; +reverse_iterator> l4{Iter<4>()}; +reverse_iterator> l5{Iter<5>()}; +reverse_iterator r{nullptr}; + +bool b0 = l0 == r; +bool b1 = l1 != r; +bool b2 = l2 < r; +bool b3 = l3 > r; +bool b4 = l4 <= r; +bool b5 = l5 >= r; + +template + concept has_eq + = requires (reverse_iterator> l, reverse_iterator r) + { l == r; }; + +template + concept has_ne + = requires (reverse_iterator> l, reverse_iterator r) + { l != r; }; + +template + concept has_lt + = requires (reverse_iterator> l, reverse_iterator r) + { l < r; }; + +template + concept has_gt + = requires (reverse_iterator> l, reverse_iterator r) + { l > r; }; + +template + concept has_le + = requires (reverse_iterator> l, reverse_iterator r) + { l <= r; }; + +template + concept has_ge + = requires (reverse_iterator> l, reverse_iterator r) + { l >= r; }; + +static_assert( has_eq<0> ); +static_assert( ! has_eq<1> ); +static_assert( ! has_eq<2> ); +static_assert( ! has_eq<3> ); +static_assert( ! has_eq<4> ); +static_assert( ! has_eq<5> ); + +static_assert( has_ne<0> ); // uses synthesized operator!= +static_assert( has_ne<1> ); +static_assert( ! has_ne<2> ); +static_assert( ! has_ne<3> ); +static_assert( ! has_ne<4> ); +static_assert( ! has_ne<5> ); + +static_assert( ! has_lt<0> ); +static_assert( ! has_lt<1> ); +static_assert( has_lt<2> ); +static_assert( ! has_lt<3> ); +static_assert( ! has_lt<4> ); +static_assert( ! has_lt<5> ); + +static_assert( ! has_gt<0> ); +static_assert( ! has_gt<1> ); +static_assert( ! has_gt<2> ); +static_assert( has_gt<3> ); +static_assert( ! has_gt<4> ); +static_assert( ! has_gt<5> ); + +static_assert( ! has_le<0> ); +static_assert( ! has_le<1> ); +static_assert( ! has_le<2> ); +static_assert( ! has_le<3> ); +static_assert( has_le<4> ); +static_assert( ! has_le<5> ); + +static_assert( ! has_ge<0> ); +static_assert( ! has_ge<1> ); +static_assert( ! has_ge<2> ); +static_assert( ! has_ge<3> ); +static_assert( ! has_ge<4> ); +static_assert( has_ge<5> );