This was approved in Wrocław as LWG 3899.
libstdc++-v3/ChangeLog:
* include/std/generator (generator::yield_value): Add overload
taking lvalue element_of view, as per LWG 3899.
---
The issue suggests that this change avoids creating a new coroutine
frame, so I thought if I used a custom allocator I'd be able to see a
reduction in memory allocation after this fix. I was unable to see any
difference. I would welcome a testcase for it.
Tested x86_64-linux.
libstdc++-v3/include/std/generator | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/libstdc++-v3/include/std/generator
b/libstdc++-v3/include/std/generator
index bba85bd0aa4..807e724c0c8 100644
--- a/libstdc++-v3/include/std/generator
+++ b/libstdc++-v3/include/std/generator
@@ -153,6 +153,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
noexcept
{ return _Recursive_awaiter { std::move(__r.range) }; }
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 3899. co_yielding elements of an lvalue generator is
+ // unnecessarily inefficient
+ template<typename _R2, typename _V2, typename _A2, typename _U2>
+ requires std::same_as<_Yield2_t<_R2, _V2>, _Yielded>
+ auto
+ yield_value(ranges::elements_of<generator<_R2, _V2, _A2>&, _U2> __r)
+ noexcept
+ { return _Recursive_awaiter { std::move(__r.range) }; }
+
template<ranges::input_range _R, typename _Alloc>
requires convertible_to<ranges::range_reference_t<_R>, _Yielded>
auto
--
2.47.1
