[PATCH 3/3] libstdc++: Fix return type of empty zip/adjacent_transform [PR106803]

[Patrick Palka via Gcc-patches]

Tested on x86_64-pc-linux-gnu, does this series look OK for trunk?

        PR libstdc++/106803

libstdc++-v3/ChangeLog:

        * include/std/ranges (views::_ZipTransform::operator()): Fix
        return type in the empty case.
        (views::_AdjacentTransform::operator()): Likewise.
---
 libstdc++-v3/include/std/ranges | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 37ad80ad3de..20eb4e82ac8 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -5071,7 +5071,7 @@ namespace views::__adaptor
        operator() [[nodiscard]] (_Fp&& __f, _Ts&&... __ts) const
        {
          if constexpr (sizeof...(_Ts) == 0)
-           return views::empty<decay_t<invoke_result_t<_Fp>>>;
+           return views::empty<decay_t<invoke_result_t<decay_t<_Fp>&>>>;
          else
            return zip_transform_view(std::forward<_Fp>(__f), 
std::forward<_Ts>(__ts)...);
        }
@@ -5762,7 +5762,7 @@ namespace views::__adaptor
          operator() [[nodiscard]] (_Range&& __r, _Fp&& __f) const
          {
            if constexpr (_Nm == 0)
-             return views::empty<tuple<>>;
+             return zip_transform(std::forward<_Fp>(__f));
            else
              return adjacent_transform_view<all_t<_Range>, decay_t<_Fp>, _Nm>
                (std::forward<_Range>(__r), std::forward<_Fp>(__f));
-- 
2.37.3.518.g79f2338b37