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libstdc++: Implement remaining P2474R2 changes to views::take/drop

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libstdc++-v3/ChangeLog:

	* include/std/ranges (views::__detail::__is_repeat_view): Define
	and later define a partial specialization.
	(views::__detail::__take_of_repeat_view): Declare and later define.
	(views::__detail::__drop_of_repeat_view): Likewise.
	(views::_Take::operator()): Return a repeat_view if the argument
	is a repeat_view as per P2474R2.
	(views::_Drop::operator()): Likewise.
	(repeat_view): Befriend __take/drop_of_repeat_view.
	* testsuite/std/ranges/repeat/1.cc (test04): New test.
This commit is contained in:
Patrick Palka 2022-10-19 15:43:13 -04:00
parent b3c98d6a59
commit fb4db9bc1c
2 changed files with 89 additions and 0 deletions
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56
libstdc++-v3/include/std/ranges
View file

@ -2257,6 +2257,13 @@ namespace views::__adaptor
template<typename _Winc, typename _Bound>
inline constexpr bool __is_iota_view<iota_view<_Winc, _Bound>> = true;
template<typename _Range>
inline constexpr bool __is_repeat_view = false;
template<typename _Range>
constexpr auto
__take_of_repeat_view(_Range&&, range_difference_t<_Range>); // defined later
template<typename _Range, typename _Dp>
concept __can_take_view
= requires { take_view(std::declval<_Range>(), std::declval<_Dp>()); };
@ -2291,6 +2298,8 @@ namespace views::__adaptor
else
return iota_view(*__begin, *__end);
}
else if constexpr (__detail::__is_repeat_view<_Tp>)
return __detail::__take_of_repeat_view(std::forward<_Range>(__r), __n);
else
return take_view(std::forward<_Range>(__r), __n);
}
@ -2527,6 +2536,10 @@ namespace views::__adaptor
{
namespace __detail
{
template<typename _Range>
constexpr auto
__drop_of_repeat_view(_Range&&, range_difference_t<_Range>); // defined later
template<typename _Range, typename _Dp>
concept __can_drop_view
= requires { drop_view(std::declval<_Range>(), std::declval<_Dp>()); };
@ -2568,6 +2581,8 @@ namespace views::__adaptor
else
return _Tp(__begin, __end);
}
else if constexpr (__detail::__is_repeat_view<_Tp>)
return __detail::__drop_of_repeat_view(std::forward<_Range>(__r), __n);
else
return drop_view(std::forward<_Range>(__r), __n);
}
@ -7367,6 +7382,14 @@ namespace views::__adaptor
struct _Iterator;
template<typename _Range>
friend constexpr auto
views::__detail::__take_of_repeat_view(_Range&&, range_difference_t<_Range>);
template<typename _Range>
friend constexpr auto
views::__detail::__drop_of_repeat_view(_Range&&, range_difference_t<_Range>);
public:
repeat_view() requires default_initializable<_Tp> = default;
@ -7540,6 +7563,9 @@ namespace views::__adaptor
{
namespace __detail
{
template<typename _Tp, typename _Bound>
inline constexpr bool __is_repeat_view<repeat_view<_Tp, _Bound>> = true;
template<typename _Tp>
concept __can_repeat_view
= requires { repeat_view(std::declval<_Tp>()); };
@ -7565,6 +7591,36 @@ namespace views::__adaptor
};
inline constexpr _Repeat repeat;
namespace __detail
{
template<typename _Range>
constexpr auto
__take_of_repeat_view(_Range&& __r, range_difference_t<_Range> __n)
{
using _Tp = remove_cvref_t<_Range>;
static_assert(__is_repeat_view<_Tp>);
if constexpr (sized_range<_Tp>)
return views::repeat(*__r._M_value, std::min(ranges::distance(__r), __n));
else
return views::repeat(*__r._M_value, __n);
}
template<typename _Range>
constexpr auto
__drop_of_repeat_view(_Range&& __r, range_difference_t<_Range> __n)
{
using _Tp = remove_cvref_t<_Range>;
static_assert(__is_repeat_view<_Tp>);
if constexpr (sized_range<_Tp>)
{
auto __sz = ranges::distance(__r);
return views::repeat(*__r._M_value, __sz - std::min(__sz, __n));
}
else
return __r;
}
}
}
template<input_range _Vp>

33
libstdc++-v3/testsuite/std/ranges/repeat/1.cc
View file

@ -84,10 +84,43 @@ test03()
return true;
}
constexpr bool
test04()
{
// Verify P2474R2 changes to views::take/drop.
auto r = views::repeat(42);
auto rt = r | views::take(10);
static_assert(views::__detail::__is_repeat_view<decltype(rt)>);
VERIFY( ranges::equal(rt, views::repeat(42, 10)) );
auto rd = r | views::drop(10);
static_assert(std::same_as<decltype(rd), decltype(r)>);
auto br = views::repeat(42, 37);
auto brt = br | views::take(10);
static_assert(std::same_as<decltype(brt), decltype(br)>);
VERIFY( ranges::equal(brt, views::repeat(42, 10)) );
auto brt100 = br | views::take(100);
VERIFY( ranges::equal(brt100, br) );
auto brd = br | views::drop(10);
static_assert(std::same_as<decltype(brd), decltype(br)>);
VERIFY( ranges::equal(brd, views::repeat(42, 27)) );
auto brd100 = br | views::drop(100);
VERIFY( ranges::empty(brd100) );
return true;
}
int
main()
{
static_assert(test01());
static_assert(test02());
static_assert(test03());
static_assert(test04());
}