On Fri, 7 Mar 2025, Tomasz Kamiński wrote:
> Add missing move_constructible && regular_invocable constrains on functor
> type,
> and is_object on functor result type for invocations of views::zip_transform
> without range arguments.
>
> PR libstdc++/111138
>
> libstdc++-v3/ChangeLog:
>
> * include/std/ranges (_ZipTransform::operator()):
> Create separate overload for calls with empty range pack,
> and add move_constructible, regular_invocable and
> is_object_v<invoke_result_t<...>>> constraints.
> * testsuite/std/ranges/zip_transform/1.cc: New tests
LGTM
> ---
> Move the empty-ranges case into separate `operator()`.
> Add missing `is_object<invoke_result_t<....>>`.
>
> Tested on x86_64-linux. OK for trunk?
>
> libstdc++-v3/include/std/ranges | 16 +++++++++-----
> .../testsuite/std/ranges/zip_transform/1.cc | 21 +++++++++++++++++++
> 2 files changed, 32 insertions(+), 5 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index e21f5284b46..97d22a12dc6 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -5331,15 +5331,21 @@ namespace views::__adaptor
>
> struct _ZipTransform
> {
> + template<typename _Fp>
> + requires move_constructible<decay_t<_Fp>> &&
> regular_invocable<decay_t<_Fp>&>
> + && is_object_v<decay_t<invoke_result_t<decay_t<_Fp>&>>>
> + constexpr auto
> + operator() [[nodiscard]] (_Fp&& __f) const
> + {
> + return views::empty<decay_t<invoke_result_t<decay_t<_Fp>&>>>;
> + }
> +
> template<typename _Fp, typename... _Ts>
> - requires (sizeof...(_Ts) == 0) ||
> __detail::__can_zip_transform_view<_Fp, _Ts...>
> + requires (sizeof...(_Ts) != 0) &&
> __detail::__can_zip_transform_view<_Fp, _Ts...>
> constexpr auto
> operator() [[nodiscard]] (_Fp&& __f, _Ts&&... __ts) const
> {
> - if constexpr (sizeof...(_Ts) == 0)
> - return views::empty<decay_t<invoke_result_t<decay_t<_Fp>&>>>;
> - else
> - return zip_transform_view(std::forward<_Fp>(__f),
> std::forward<_Ts>(__ts)...);
> + return zip_transform_view(std::forward<_Fp>(__f),
> std::forward<_Ts>(__ts)...);
> }
> };
>
> diff --git a/libstdc++-v3/testsuite/std/ranges/zip_transform/1.cc
> b/libstdc++-v3/testsuite/std/ranges/zip_transform/1.cc
> index 20abdcba0f8..9a0ad3814e6 100644
> --- a/libstdc++-v3/testsuite/std/ranges/zip_transform/1.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/zip_transform/1.cc
> @@ -9,6 +9,23 @@
> namespace ranges = std::ranges;
> namespace views = std::views;
>
> +template<typename T>
> +concept can_zip_transform = requires (T t) {
> + views::zip_transform(std::forward<T>(t));
> +};
> +
> +static_assert(!can_zip_transform<int>);
> +
> +struct NonMovable {
> + NonMovable(NonMovable&&) = delete;
> +};
> +
> +static_assert(!can_zip_transform<NonMovable>);
> +static_assert(!can_zip_transform<NonMovable&>);
> +
> +static_assert(!can_zip_transform<void(*)()>);
> +static_assert(can_zip_transform<int(&(*)())[3]>);
> +
> constexpr bool
> test01()
> {
> @@ -46,6 +63,10 @@ test01()
> VERIFY( ranges::size(z3) == 3 );
> VERIFY( ranges::equal(z3, (int[]){3, 6, 9}) );
>
> + auto z4 = views::zip_transform([] () { return 1; });
> + VERIFY( ranges::size(z4) == 0 );
> + static_assert( std::same_as<ranges::range_value_t<decltype(z4)>, int> );
> +
> return true;
> }
>
> --
> 2.48.1
>
>
