[libcxx] Add deduction guides for shared_ptr and weak_ptr

[logan-5]

Summary

This patch adds deduction guides to <memory> to allow deducing construction of shared_ptrs from unique_ptrs, and from weak_ptrs and vice versa, as specified by C++17.

[logan-5]

Add a newline to synopsis

[mclow.lists]

The tests should be more comprehensive; they should ASSERT_SAME_TYPE(decltype(s), XXX) to make sure that the deduction guides actually return the correct type, rather than just compile.

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/deduction.pass.cpp

25

When you're testing type-deduction, I find it much easier to convince myself that the types are correct if you are explicit whenever possible (instead of just auto everywhere)
Example:

using SP = std::shared_ptr<A>;
using WP = std::weak_ptr<A>;

SP s0 = new A;
WP w = s0;
auto s = std::shared_ptr(w);
ASSERT_SAME_TYPE(decltype(s), SP);

Also, you should check the value of s. Make sure it points to the same thing as s0.

[logan-5]

Beefed up the tests in response to some feedback -- thanks.

[logan-5]

ping

[logan-5]

Hello! Pinging this again.

[mclow.lists]

This looks good to me now.
You need to update www/cxx17_status.html appropriately as well.

[logan-5]

Thanks Marshall. As for www/cxx1z_status.html, my best guess is that it doesn't need updating, since the row for P0433R2 lists it as In progress, which I believe is still the case after this patch. Please correct me if I'm wrong. Otherwise, I'd be grateful if someone with commit access could help me tie a bow around this.

[logan-5]

Giving this another ping--I just need someone to help me commit this.

[logan-5]

Ping.

[ldionne]

Thanks! Committed as

commit 83564056d4b186c9fcf016cdbb388755009f7b5a
Author: Logan Smith <[e-mail]>
Date:   Thu May 7 12:07:01 2020 -0400

    [libcxx] Add deduction guides for shared_ptr and weak_ptr

    This patch adds deduction guides to <memory> to allow deducing
    construction of shared_ptrs from unique_ptrs, and from weak_ptrs
    and vice versa, as specified by C++17.

    Differential Revision: https://reviews.llvm.org/D69603

[ldionne]

This fails under the asan bot. @logan-5 Can you please take a look? http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-ubuntu-asan/builds/3235/steps/test.libcxx/logs/FAIL%3A%20libc%2B%2B%3A%3Adeduction.pass.cpp

[logan-5]

Ack. It fails because there's a leak because a dummy deleter I used (D in deduction.pass.cpp) is a no-op. I suppose it should delete its argument as expected.

Should I submit another patch? Or does someone have the power to just commit the fix directly?

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/deduction.pass.cpp

26

Here's the offending line.

[zoecarver]

@logan-5 Fixed: afc8b49782f37524ccde82c54a9a2eb09a40f869

[ldionne]

In D69603#2027474, @zoecarver wrote:

@logan-5 Fixed: afc8b49782f37524ccde82c54a9a2eb09a40f869

Thanks to both of you!

libcxx/include/memory

public:
     T* operator->() const noexcept;
     long use_count() const noexcept;
     bool unique() const noexcept;
     explicit operator bool() const noexcept;
     template<class U> bool owner_before(shared_ptr<U> const& b) const noexcept;
     template<class U> bool owner_before(weak_ptr<U> const& b) const noexcept;
 };
 
+template<class T>
+shared_ptr(weak_ptr<T>) -> shared_ptr<T>;
+template<class T, class D>
+shared_ptr(unique_ptr<T, D>) -> shared_ptr<T>;
+
 // shared_ptr comparisons:
 template<class T, class U>
     bool operator==(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
 template<class T, class U>
     bool operator!=(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
 template<class T, class U>
     bool operator<(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
 template<class T, class U>
public:
     // observers
     long use_count() const noexcept;
     bool expired() const noexcept;
     shared_ptr<T> lock() const noexcept;
     template<class U> bool owner_before(shared_ptr<U> const& b) const noexcept;
     template<class U> bool owner_before(weak_ptr<U> const& b) const noexcept;
 };
 
+template<class T>
+weak_ptr(shared_ptr<T>) -> weak_ptr<T>;
+
 // weak_ptr specialized algorithms:
 template<class T> void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;
 
 // class owner_less:
 template<class T> struct owner_less;
 
 template<class T>
 struct owner_less<shared_ptr<T> >
template <class _Yp, class _OrigPtr>
         }
 
     _LIBCPP_INLINE_VISIBILITY void __enable_weak_this(...) _NOEXCEPT {}
 
     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
 };
 
+#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
+template<class _Tp>
+shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
+template<class _Tp, class _Dp>
+shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
+#endif
 
 template<class _Tp>
 inline
 _LIBCPP_CONSTEXPR
 shared_ptr<_Tp>::shared_ptr() _NOEXCEPT
     : __ptr_(0),
       __cntrl_(0)
 {
template<class _Up>
         _LIBCPP_INLINE_VISIBILITY
         bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT
         {return __cntrl_ < __r.__cntrl_;}
 
     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
 };
 
+#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
+template<class _Tp>
+weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
+#endif
+
 template<class _Tp>
 inline
 _LIBCPP_CONSTEXPR
 weak_ptr<_Tp>::weak_ptr() _NOEXCEPT
     : __ptr_(0),
       __cntrl_(0)
 {
 }

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/deduction.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// UNSUPPORTED: libcpp-no-deduction-guides
+
+// template<class T> class shared_ptr
+
+// shared_ptr(weak_ptr<T>) -> shared_ptr<T>
+// shared_ptr(unique_ptr<T>) -> shared_ptr<T>
+
+#include <memory>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A {};
+
+struct D {
+  void operator()(void*) const {}
+};
+
+int main(int, char**)
+{
+  {
+    std::shared_ptr<A> s0(new A);
+    std::weak_ptr<A> w = s0;
+    auto s = std::shared_ptr(w);
+    ASSERT_SAME_TYPE(decltype(s), std::shared_ptr<A>);
+    assert(s0.use_count() == 2);
+    assert(s.use_count() == 2);
+    assert(s0.get() == s.get());
+  }
+  {
+    std::unique_ptr<A> u(new A);
+    A* const uPointee = u.get();
+    std::shared_ptr s = std::move(u);
+    ASSERT_SAME_TYPE(decltype(s), std::shared_ptr<A>);
+    assert(u == nullptr);
+    assert(s.get() == uPointee);
+  }
+  {
+    std::unique_ptr<A, D> u(new A, D{});
+    A* const uPointee = u.get();
+    std::shared_ptr s(std::move(u));
+    ASSERT_SAME_TYPE(decltype(s), std::shared_ptr<A>);
+    assert(u == nullptr);
+    assert(s.get() == uPointee);
+  }
+
+  return 0;
+}

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.weak/util.smartptr.weak.const/shared_ptr_deduction.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// UNSUPPORTED: libcpp-no-deduction-guides
+
+// template<class T> class weak_ptr
+
+// weak_ptr(shared_ptr<T>) -> weak_ptr<T>
+
+#include <memory>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A {};
+
+int main(int, char**)
+{
+  std::shared_ptr<A> s(new A);
+  auto w = std::weak_ptr(s);
+  ASSERT_SAME_TYPE(decltype(w), std::weak_ptr<A>);
+  assert(!w.expired());
+  assert(w.use_count() == 1);
+  assert(w.lock().get() == s.get());
+
+  return 0;
+}