From 5edc0c15f1667cc2a5deb664b25c007b35d259f6 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 10 May 2021 20:46:38 +0100
Subject: [PATCH] libstdc++: Implement proposed resolution to LWG 3548
This has been tentatively approved by LWG. The deleter from a unique_ptr
can be moved into the shared_ptr (at least, since LWG 2802). This uses
std::forward<_Del>(__r.get_deleter()) not std::move(__r.get_deleter())
because we don't want to convert the deleter to an rvalue when _Del is
an lvalue reference type.
This also adds a missing is_move_constructible_v<D> constraint to the
shared_ptr(unique_ptr<Y, D>&&) constructor, which is inherited from the
shared_ptr(Y*, D) constructor due to the use of "equivalent to" in the
specified effects.
libstdc++-v3/ChangeLog:
* include/bits/shared_ptr_base.h (__shared_count(unique_ptr&&)):
Initialize a non-reference deleter from an rvalue, as per LWG
3548.
(__shared_ptr::_UniqCompatible): Add missing constraint.
* testsuite/20_util/shared_ptr/cons/lwg3548.cc: New test.
* testsuite/20_util/shared_ptr/cons/unique_ptr_deleter.cc: Check
constraints.
---
libstdc++-v3/include/bits/shared_ptr_base.h | 13 +++++++++----
.../20_util/shared_ptr/cons/lwg3548.cc | 16 ++++++++++++++++
.../shared_ptr/cons/unique_ptr_deleter.cc | 17 ++++++++++++++++-
3 files changed, 41 insertions(+), 5 deletions(-)
create mode 100644 libstdc++-v3/testsuite/20_util/shared_ptr/cons/lwg3548.cc
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index 71099afbf7a4..eb9ad23ba1e3 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -684,8 +684,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using _Alloc_traits = allocator_traits<_Alloc>;
_Alloc __a;
_Sp_cd_type* __mem = _Alloc_traits::allocate(__a, 1);
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 3548. shared_ptr construction from unique_ptr should move
+ // (not copy) the deleter
_Alloc_traits::construct(__a, __mem, __r.release(),
- __r.get_deleter()); // non-throwing
+ std::forward<_Del>(__r.get_deleter()));
_M_pi = __mem;
}
@@ -1070,9 +1073,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Constraint for construction from unique_ptr:
template<typename _Yp, typename _Del, typename _Res = void,
typename _Ptr = typename unique_ptr<_Yp, _Del>::pointer>
- using _UniqCompatible = typename enable_if<__and_<
- __sp_compatible_with<_Yp*, _Tp*>, is_convertible<_Ptr, element_type*>
- >::value, _Res>::type;
+ using _UniqCompatible = __enable_if_t<__and_<
+ __sp_compatible_with<_Yp*, _Tp*>,
+ is_convertible<_Ptr, element_type*>,
+ is_move_constructible<_Del>
+ >::value, _Res>;
// Constraint for assignment from unique_ptr:
template<typename _Yp, typename _Del>
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/lwg3548.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/lwg3548.cc
new file mode 100644
index 000000000000..d6ec7b1d0578
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/lwg3548.cc
@@ -0,0 +1,16 @@
+// { dg-do compile { target c++11 } }
+
+#include <memory>
+
+// LWG 3548
+// shared_ptr construction from unique_ptr should move (not copy) the deleter
+
+struct D
+{
+ D() { }
+ D(D&&) { }
+ void operator()(int* p) const { delete p; }
+};
+
+std::unique_ptr<int, D> u;
+std::shared_ptr<int> s1(std::move(u));
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/unique_ptr_deleter.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/unique_ptr_deleter.cc
index f4cf3ddda2e4..d7ca51a4aa6e 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/unique_ptr_deleter.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/unique_ptr_deleter.cc
@@ -58,10 +58,25 @@ test02()
VERIFY( D::count == 0 ); // LWG 2415
}
+void
+test03()
+{
+ struct D
+ {
+ D() = default;
+ D(const D&) = delete; // not copyable or movable
+ void operator()(int* p) const { delete p; }
+ };
+
+ using namespace std;
+ static_assert( ! is_constructible<shared_ptr<int>, unique_ptr<int, D>>(),
+ "Constraints: is_move_constructible_v<D> is true" );
+}
+
int
main()
{
test01();
test02();
- return 0;
+ test03();
}
--
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