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.
Tested powerpc64le-linux. Committed to trunk.
This should be backported to gcc-10.
commit aecea4158f4e547af349657a3d16cb031a30ec3b
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Mon Sep 21 23:43:25 2020
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.
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 005e89f94b2..1bf894dd570 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2238,7 +2238,10 @@ namespace views
_Vp _M_base = _Vp();
range_difference_t<_Vp> _M_count = 0;
- static constexpr bool _S_needs_cached_begin = !random_access_range<_Vp>;
+ // ranges::next(begin(base), count, end(base)) is O(1) if _Vp satisfies
+ // both random_access_range and sized_range. Otherwise, cache its result.
+ static constexpr bool _S_needs_cached_begin
+ = !(random_access_range<const _Vp> && sized_range<const _Vp>);
[[no_unique_address]]
__detail::__maybe_present_t<_S_needs_cached_begin,
__detail::_CachedPosition<_Vp>>
@@ -2260,9 +2263,12 @@ namespace views
base() &&
{ return std::move(_M_base); }
+ // This overload is disabled for simple views with constant-time begin().
constexpr auto
- begin() requires (!(__detail::__simple_view<_Vp>
- && random_access_range<_Vp>))
+ begin()
+ requires (!(__detail::__simple_view<_Vp>
+ && random_access_range<const _Vp>
+ && sized_range<const _Vp>))
{
if constexpr (_S_needs_cached_begin)
if (_M_cached_begin._M_has_value())
@@ -2275,8 +2281,11 @@ namespace views
return __it;
}
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 3482. drop_view's const begin should additionally require sized_range
constexpr auto
- begin() const requires random_access_range<const _Vp>
+ begin() const
+ requires random_access_range<const _Vp> && sized_range<const _Vp>
{
return ranges::next(ranges::begin(_M_base), _M_count,
ranges::end(_M_base));
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/drop.cc
b/libstdc++-v3/testsuite/std/ranges/adaptors/drop.cc
index 3c82caea772..5fe94b67507 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/drop.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/drop.cc
@@ -26,6 +26,7 @@
using __gnu_test::test_range;
using __gnu_test::forward_iterator_wrapper;
using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::random_access_iterator_wrapper;
namespace ranges = std::ranges;
namespace views = ranges::views;
@@ -123,21 +124,6 @@ struct test_wrapper : forward_iterator_wrapper<T>
forward_iterator_wrapper<T>::operator++();
return *this;
}
-
- test_wrapper
- operator--(int)
- {
- auto tmp = *this;
- --*this;
- return tmp;
- }
-
- test_wrapper&
- operator--()
- {
- forward_iterator_wrapper<T>::operator--();
- return *this;
- }
};
void
@@ -146,11 +132,132 @@ test07()
int x[] = {1,2,3,4,5};
test_range<int, test_wrapper> rx(x);
auto v = rx | views::drop(3);
+ VERIFY( test_wrapper<int>::increment_count == 0 );
+ (void) v.begin();
+ VERIFY( test_wrapper<int>::increment_count == 3 );
+ (void) v.begin();
+ VERIFY( test_wrapper<int>::increment_count == 3 );
VERIFY( ranges::equal(v, (int[]){4,5}) );
+ VERIFY( test_wrapper<int>::increment_count == 5 );
VERIFY( ranges::equal(v, (int[]){4,5}) );
VERIFY( test_wrapper<int>::increment_count == 7 );
}
+template<typename T>
+struct ra_test_wrapper : random_access_iterator_wrapper<T>
+{
+ static inline int increment_count = 0;
+
+ using random_access_iterator_wrapper<T>::random_access_iterator_wrapper;
+
+ ra_test_wrapper() : random_access_iterator_wrapper<T>()
+ { }
+
+ ra_test_wrapper
+ operator++(int)
+ {
+ auto tmp = *this;
+ ++*this;
+ return tmp;
+ }
+
+ ra_test_wrapper&
+ operator++()
+ {
+ ++increment_count;
+ random_access_iterator_wrapper<T>::operator++();
+ return *this;
+ }
+
+ ra_test_wrapper
+ operator--(int)
+ {
+ auto tmp = *this;
+ --*this;
+ return tmp;
+ }
+
+ ra_test_wrapper&
+ operator--()
+ {
+ random_access_iterator_wrapper<T>::operator--();
+ return *this;
+ }
+
+ ra_test_wrapper&
+ operator+=(std::ptrdiff_t n)
+ {
+ random_access_iterator_wrapper<T>::operator+=(n);
+ return *this;
+ }
+
+ ra_test_wrapper&
+ operator-=(std::ptrdiff_t n)
+ { return *this += -n; }
+
+ ra_test_wrapper
+ operator+(std::ptrdiff_t n) const
+ {
+ auto tmp = *this;
+ return tmp += n;
+ }
+
+ ra_test_wrapper
+ operator-(std::ptrdiff_t n) const
+ {
+ auto tmp = *this;
+ return tmp -= n;
+ }
+
+ std::ptrdiff_t
+ operator-(const ra_test_wrapper& it) const
+ {
+ return static_cast<const random_access_iterator_wrapper<T>&>(*this) - it;
+ }
+
+ friend ra_test_wrapper
+ operator+(std::ptrdiff_t n, const ra_test_wrapper& it)
+ { return it + n; }
+};
+
+void
+test08()
+{
+ // LWG 3482 - drop_view's const begin should additionally require sized_range
+
+ short a[10]{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+ test_range<short, ra_test_wrapper> ra(a);
+ static_assert( ranges::random_access_range<decltype(ra)> );
+ ranges::subrange nonsized = {ra.begin(), std::unreachable_sentinel};
+ using Nonsized = decltype(nonsized);
+ static_assert( ranges::random_access_range<Nonsized> );
+ static_assert( ! ranges::sized_range<Nonsized> );
+ auto v1 = nonsized | views::drop(5);
+ VERIFY( ra_test_wrapper<short>::increment_count == 0 );
+ auto b1 = v1.begin();
+ VERIFY( ra_test_wrapper<short>::increment_count == 5 );
+ VERIFY( v1.begin() == b1 );
+ VERIFY( ra_test_wrapper<short>::increment_count == 5 );
+ VERIFY( *b1 == 5 );
+ VERIFY( *v1.begin() == 5 );
+ VERIFY( ra_test_wrapper<short>::increment_count == 5 );
+
+ long b[10]{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+ test_range<long, ra_test_wrapper> rb(b);
+ ranges::subrange sized = {rb.begin(), rb.begin()+6};
+ using Sized = decltype(sized);
+ static_assert( ranges::random_access_range<Sized> );
+ static_assert( ranges::sized_range<Sized> );
+ auto v2 = sized | views::drop(6);
+ auto b2 = v2.begin();
+ VERIFY( ra_test_wrapper<long>::increment_count == 0 );
+ VERIFY( v2.begin() == b2 );
+ VERIFY( ra_test_wrapper<long>::increment_count == 0 );
+ VERIFY( *b2 == 6 );
+ VERIFY( *v2.begin() == 6 );
+ VERIFY( ra_test_wrapper<long>::increment_count == 0 );
+}
+
int
main()
{
@@ -161,4 +268,5 @@ main()
test05();
test06();
test07();
+ test08();
}
