https://gcc.gnu.org/g:49e79b86936373fc70c3bdea3b2d8353cf8957b1
commit r16-87-g49e79b86936373fc70c3bdea3b2d8353cf8957b1
Author: Patrick Palka <ppa...@redhat.com>
Date: Tue Apr 22 12:52:34 2025 -0400
Revert "libstdc++: Optimize std::projected<I, std::identity>" [PR119888]
This non-standard optimization breaks real-world code that expects the
result of std::projected to always (be a class type and) have a value_type
member, which isn't true for e.g. I=int*, so revert it for now.
PR libstdc++/119888
This reverts commit 51761c50f843d5be4e24172535e4524b5072f24c.
Diff:
---
libstdc++-v3/include/bits/iterator_concepts.h | 5 -----
libstdc++-v3/testsuite/24_iterators/indirect_callable/projected.cc | 5 -----
2 files changed, 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/iterator_concepts.h
b/libstdc++-v3/include/bits/iterator_concepts.h
index e36556dc5121..3b73ff9b6b59 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -829,11 +829,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using __projected_Proj = _Proj;
};
};
-
- // Optimize the common case of the projection being std::identity.
- template<typename _Iter>
- struct __projected<_Iter, identity>
- { using __type = _Iter; };
} // namespace __detail
/// [projected], projected
diff --git a/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected.cc
b/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected.cc
index 0b18616aa8b7..e2fbf7dccb9c 100644
--- a/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected.cc
+++ b/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected.cc
@@ -22,12 +22,7 @@
template<typename T>
using PI = std::projected<T, std::identity>;
-#if __GLIBCXX__
-// Verify our projected<I, identity> optimization.
-static_assert(std::same_as<PI<int*>, int*>);
-#else
static_assert(std::same_as<PI<int*>::value_type, int>);
-#endif
static_assert(std::same_as<decltype(*std::declval<const PI<int*>&>()), int&>);
struct X
