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libstdc++: Apply proposed resolution for LWG 3449 [PR95322]

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Now that the frontend bug PR96805 is fixed, we can cleanly apply the
proposed resolution for this issue.

This slightly deviates from the proposed resolution by declaring _CI a
member of take_view instead of take_view::_Sentinel, since it doesn't
depend on anything within _Sentinel anymore.

libstdc++-v3/ChangeLog:

	PR libstdc++/95322
	* include/std/ranges (take_view::_CI): Define this alias
	template as per LWG 3449 and remove ...
	(take_view::_Sentinel::_CI): ... this type alias.
	(take_view::_Sentinel::operator==): Adjust use of _CI
	accordingly.  Define a second overload that accepts an iterator
	of the opposite constness as per LWG 3449.
	(take_while_view::_Sentinel::operator==): Likewise.
	* testsuite/std/ranges/adaptors/95322.cc: Add tests for LWG 3449.
This commit is contained in:
Patrick Palka 2020-10-12 13:46:21 -04:00
parent c840700852
commit e066821b6f
2 changed files with 47 additions and 4 deletions
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23
libstdc++-v3/include/std/ranges
View File

@ -1662,13 +1662,15 @@ namespace views
class take_view : public view_interface<take_view<_Vp>>
{
private:
template<bool _Const>
using _CI = counted_iterator<
iterator_t<__detail::__maybe_const_t<_Const, _Vp>>>;
template<bool _Const>
struct _Sentinel
{
private:
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
using _CI = counted_iterator<iterator_t<_Base>>;
sentinel_t<_Base> _M_end = sentinel_t<_Base>();
public:
@ -1689,7 +1691,15 @@ namespace views
base() const
{ return _M_end; }
friend constexpr bool operator==(const _CI& __y, const _Sentinel& __x)
friend constexpr bool
operator==(const _CI<_Const>& __y, const _Sentinel& __x)
{ return __y.count() == 0 || __y.base() == __x._M_end; }
template<bool _OtherConst = !_Const,
typename _Base2 = __detail::__maybe_const_t<_OtherConst, _Vp>>
requires sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
friend constexpr bool
operator==(const _CI<_OtherConst>& __y, const _Sentinel& __x)
{ return __y.count() == 0 || __y.base() == __x._M_end; }
friend _Sentinel<!_Const>;
@ -1839,6 +1849,13 @@ namespace views
operator==(const iterator_t<_Base>& __x, const _Sentinel& __y)
{ return __y._M_end == __x || !std::__invoke(*__y._M_pred, *__x); }
template<bool _OtherConst = !_Const,
typename _Base2 = __detail::__maybe_const_t<_OtherConst, _Vp>>
requires sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
friend constexpr bool
operator==(const iterator_t<_Base2>& __x, const _Sentinel& __y)
{ return __y._M_end == __x || !std::__invoke(*__y._M_pred, *__x); }
friend _Sentinel<!_Const>;
};

28
libstdc++-v3/testsuite/std/ranges/adaptors/95322.cc
View File

@ -26,7 +26,7 @@ using __gnu_test::test_forward_range;
void
test01()
{
// PR libstdc++/95322 and LWG 3488
// PR libstdc++/95322 and LWG 3448
int a[2]{1, 2};
test_forward_range<int> v{a};
auto view1 = v | std::views::take(2);
@ -51,8 +51,34 @@ test02()
VERIFY( !eq );
}
void
test03()
{
// LWG 3449, for take_view
int a[2]{1, 2};
test_forward_range<int> v{a};
auto view1 = v | std::views::transform(std::identity{});
auto view2 = view1 | std::views::take(2);
const bool eq = std::ranges::cbegin(view2) == std::ranges::end(view2);
VERIFY( !eq );
}
void
test04()
{
// LWG 3449, for take_while_view
int a[2]{1, 2};
test_forward_range<int> v{a};
auto view1 = v | std::views::transform(std::identity{});
auto view2 = view1 | std::views::take_while([] (int i) { return true; });
const bool eq = std::ranges::cbegin(view2) == std::ranges::end(view2);
VERIFY( !eq );
}
int main()
{
test01();
test02();
test03();
test04();
}