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libstdc++: Implement LWG 3564 for ranges::transform_view

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The _Iterator<true> type returned by begin() const uses const F& to
transform the elements, so it should use const F& to determine the
iterator's value_type and iterator_category as well.

This was accepted into the WP in July 2022.

libstdc++-v3/ChangeLog:

	* include/std/ranges (transform_view:_Iterator): Use const F&
	to determine value_type and iterator_category of
	_Iterator<true>, as per LWG 3564.
	* testsuite/std/ranges/adaptors/transform.cc: Check value_type
	and iterator_category.

Reviewed-by: Patrick Palka <ppalka@redhat.com>
This commit is contained in:
Jonathan Wakely 2024-10-13 21:47:14 +01:00 committed by Jonathan Wakely
parent cacbb4daac
commit dde19c600c
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2 changed files with 26 additions and 2 deletions
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9
libstdc++-v3/include/std/ranges
View File

@ -1886,8 +1886,12 @@ namespace views::__adaptor
static auto
_S_iter_cat()
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3564. transform_view::iterator<true>::value_type and
// iterator_category should use const F&
using _Base = transform_view::_Base<_Const>;
using _Res = invoke_result_t<_Fp&, range_reference_t<_Base>>;
using _Res = invoke_result_t<__maybe_const_t<_Const, _Fp>&,
range_reference_t<_Base>>;
if constexpr (is_lvalue_reference_v<_Res>)
{
using _Cat
@ -1936,7 +1940,8 @@ namespace views::__adaptor
using iterator_concept = decltype(_S_iter_concept());
// iterator_category defined in __transform_view_iter_cat
using value_type
= remove_cvref_t<invoke_result_t<_Fp&, range_reference_t<_Base>>>;
= remove_cvref_t<invoke_result_t<__maybe_const_t<_Const, _Fp>&,
range_reference_t<_Base>>>;
using difference_type = range_difference_t<_Base>;
_Iterator() requires default_initializable<_Base_iter> = default;

19
libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
View File

@ -196,6 +196,24 @@ test09()
#endif
}
void
test10()
{
struct F {
short operator()(int) { return 0; }
const int& operator()(const int& i) const { return i; }
};
int x[] {2, 4};
const auto xform = x | views::transform(F{});
using const_iterator = decltype(xform.begin());
// LWG 3564. transform_view::iterator<true>::value_type and iterator_category
// should use const F&
static_assert(std::same_as<std::iter_value_t<const_iterator>, int>);
using cat = std::iterator_traits<const_iterator>::iterator_category;
static_assert(std::same_as<cat, std::random_access_iterator_tag>);
}
int
main()
{
@ -208,4 +226,5 @@ main()
test07();
test08();
test09();
test10();
}