libstdc++: Fix constraints for drop_view::begin() const [LWG 3482]
libstdc++-v3/ChangeLog: * include/std/ranges (drop_view::begin()): Adjust constraints to match the correct condition for O(1) ranges::next (LWG 3482). * testsuite/std/ranges/adaptors/drop.cc: Check that iterator is cached for non-sized_range.
This commit is contained in:
Jonathan Wakely
parent
be3027e9c8
commit
aecea4158f
2 changed files with 136 additions and 19 deletions
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@ -2238,7 +2238,10 @@ namespace views
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_Vp _M_base = _Vp();
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range_difference_t<_Vp> _M_count = 0;
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static constexpr bool _S_needs_cached_begin = !random_access_range<_Vp>;
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// ranges::next(begin(base), count, end(base)) is O(1) if _Vp satisfies
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// both random_access_range and sized_range. Otherwise, cache its result.
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static constexpr bool _S_needs_cached_begin
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= !(random_access_range<const _Vp> && sized_range<const _Vp>);
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[[no_unique_address]]
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__detail::__maybe_present_t<_S_needs_cached_begin,
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__detail::_CachedPosition<_Vp>>
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@ -2260,9 +2263,12 @@ namespace views
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base() &&
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{ return std::move(_M_base); }
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// This overload is disabled for simple views with constant-time begin().
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constexpr auto
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begin() requires (!(__detail::__simple_view<_Vp>
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&& random_access_range<_Vp>))
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begin()
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requires (!(__detail::__simple_view<_Vp>
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&& random_access_range<const _Vp>
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&& sized_range<const _Vp>))
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{
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if constexpr (_S_needs_cached_begin)
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if (_M_cached_begin._M_has_value())
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@ -2275,8 +2281,11 @@ namespace views
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return __it;
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}
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// _GLIBCXX_RESOLVE_LIB_DEFECTS
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// 3482. drop_view's const begin should additionally require sized_range
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constexpr auto
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begin() const requires random_access_range<const _Vp>
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begin() const
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requires random_access_range<const _Vp> && sized_range<const _Vp>
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{
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return ranges::next(ranges::begin(_M_base), _M_count,
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ranges::end(_M_base));
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@ -26,6 +26,7 @@
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using __gnu_test::test_range;
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using __gnu_test::forward_iterator_wrapper;
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using __gnu_test::bidirectional_iterator_wrapper;
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using __gnu_test::random_access_iterator_wrapper;
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namespace ranges = std::ranges;
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namespace views = ranges::views;
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@ -123,21 +124,6 @@ struct test_wrapper : forward_iterator_wrapper<T>
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forward_iterator_wrapper<T>::operator++();
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return *this;
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}
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test_wrapper
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operator--(int)
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{
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auto tmp = *this;
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--*this;
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return tmp;
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}
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test_wrapper&
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operator--()
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{
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forward_iterator_wrapper<T>::operator--();
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return *this;
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}
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};
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void
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@ -146,11 +132,132 @@ test07()
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int x[] = {1,2,3,4,5};
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test_range<int, test_wrapper> rx(x);
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auto v = rx | views::drop(3);
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VERIFY( test_wrapper<int>::increment_count == 0 );
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(void) v.begin();
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VERIFY( test_wrapper<int>::increment_count == 3 );
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(void) v.begin();
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VERIFY( test_wrapper<int>::increment_count == 3 );
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VERIFY( ranges::equal(v, (int[]){4,5}) );
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VERIFY( test_wrapper<int>::increment_count == 5 );
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VERIFY( ranges::equal(v, (int[]){4,5}) );
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VERIFY( test_wrapper<int>::increment_count == 7 );
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}
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template<typename T>
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struct ra_test_wrapper : random_access_iterator_wrapper<T>
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{
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static inline int increment_count = 0;
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using random_access_iterator_wrapper<T>::random_access_iterator_wrapper;
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ra_test_wrapper() : random_access_iterator_wrapper<T>()
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{ }
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ra_test_wrapper
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operator++(int)
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{
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auto tmp = *this;
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++*this;
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return tmp;
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}
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ra_test_wrapper&
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operator++()
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{
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++increment_count;
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random_access_iterator_wrapper<T>::operator++();
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return *this;
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}
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ra_test_wrapper
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operator--(int)
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{
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auto tmp = *this;
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--*this;
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return tmp;
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}
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ra_test_wrapper&
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operator--()
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{
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random_access_iterator_wrapper<T>::operator--();
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return *this;
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}
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ra_test_wrapper&
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operator+=(std::ptrdiff_t n)
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{
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random_access_iterator_wrapper<T>::operator+=(n);
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return *this;
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}
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ra_test_wrapper&
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operator-=(std::ptrdiff_t n)
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{ return *this += -n; }
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ra_test_wrapper
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operator+(std::ptrdiff_t n) const
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{
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auto tmp = *this;
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return tmp += n;
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}
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ra_test_wrapper
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operator-(std::ptrdiff_t n) const
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{
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auto tmp = *this;
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return tmp -= n;
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}
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std::ptrdiff_t
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operator-(const ra_test_wrapper& it) const
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{
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return static_cast<const random_access_iterator_wrapper<T>&>(*this) - it;
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}
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friend ra_test_wrapper
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operator+(std::ptrdiff_t n, const ra_test_wrapper& it)
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{ return it + n; }
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};
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void
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test08()
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{
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// LWG 3482 - drop_view's const begin should additionally require sized_range
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short a[10]{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
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test_range<short, ra_test_wrapper> ra(a);
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static_assert( ranges::random_access_range<decltype(ra)> );
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ranges::subrange nonsized = {ra.begin(), std::unreachable_sentinel};
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using Nonsized = decltype(nonsized);
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static_assert( ranges::random_access_range<Nonsized> );
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static_assert( ! ranges::sized_range<Nonsized> );
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auto v1 = nonsized | views::drop(5);
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VERIFY( ra_test_wrapper<short>::increment_count == 0 );
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auto b1 = v1.begin();
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VERIFY( ra_test_wrapper<short>::increment_count == 5 );
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VERIFY( v1.begin() == b1 );
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VERIFY( ra_test_wrapper<short>::increment_count == 5 );
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VERIFY( *b1 == 5 );
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VERIFY( *v1.begin() == 5 );
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VERIFY( ra_test_wrapper<short>::increment_count == 5 );
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long b[10]{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
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test_range<long, ra_test_wrapper> rb(b);
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ranges::subrange sized = {rb.begin(), rb.begin()+6};
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using Sized = decltype(sized);
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static_assert( ranges::random_access_range<Sized> );
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static_assert( ranges::sized_range<Sized> );
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auto v2 = sized | views::drop(6);
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auto b2 = v2.begin();
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VERIFY( ra_test_wrapper<long>::increment_count == 0 );
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VERIFY( v2.begin() == b2 );
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VERIFY( ra_test_wrapper<long>::increment_count == 0 );
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VERIFY( *b2 == 6 );
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VERIFY( *v2.begin() == 6 );
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VERIFY( ra_test_wrapper<long>::increment_count == 0 );
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}
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int
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main()
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{
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@ -161,4 +268,5 @@ main()
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test05();
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test06();
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test07();
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test08();
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}
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