On Mon, 14 Oct 2024, Jonathan Wakely wrote:
> Tested x86_64-linux.
>
> -- >8 --
>
> 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.
> ---
> libstdc++-v3/include/std/ranges | 9 +++++++--
> .../std/ranges/adaptors/transform.cc | 19 +++++++++++++++++++
> 2 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 6e6e3b97d82..f0d81cbea0c 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -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 _Fpc = __detail::__maybe_const_t<_Const, _Fp>;
We can use __maybe_const_t unqualified here (ever since
r13-3758-gf471cb71c86c1e).
> using _Base = transform_view::_Base<_Const>;
> - using _Res = invoke_result_t<_Fp&, range_reference_t<_Base>>;
> + using _Res = invoke_result_t<_Fpc&, range_reference_t<_Base>>;
> if constexpr (is_lvalue_reference_v<_Res>)
> {
> using _Cat
> @@ -1927,6 +1931,7 @@ namespace views::__adaptor
> return input_iterator_tag{};
> }
>
> + using _Fpc = __detail::__maybe_const_t<_Const, _Fp>;
Same here. LGTM besides that.
> using _Base_iter = iterator_t<_Base>;
>
> _Base_iter _M_current = _Base_iter();
> @@ -1936,7 +1941,7 @@ 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<_Fpc&, range_reference_t<_Base>>>;
> using difference_type = range_difference_t<_Base>;
>
> _Iterator() requires default_initializable<_Base_iter> = default;
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> b/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> index bcb18a3fc6c..ca695349650 100644
> --- a/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> @@ -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();
> }
> --
> 2.46.2
>
>
