From 513cd15378259284f212dd725d9989e36058e206 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 21 Apr 2019 22:43:04 +0300
Subject: [PATCH] Add aliasing constructors to weak_ptr. Closes #67.

---
 include/boost/smart_ptr/weak_ptr.hpp | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/boost/smart_ptr/weak_ptr.hpp b/include/boost/smart_ptr/weak_ptr.hpp
index 54d9ef3..ec451bd 100644
--- a/include/boost/smart_ptr/weak_ptr.hpp
+++ b/include/boost/smart_ptr/weak_ptr.hpp
@@ -137,6 +137,23 @@ public:
         boost::detail::sp_assert_convertible< Y, T >();
     }
 
+    // aliasing
+    template<class Y> weak_ptr(shared_ptr<Y> const & r, element_type * p) BOOST_SP_NOEXCEPT: px( p ), pn( r.pn )
+    {
+    }
+
+    template<class Y> weak_ptr(weak_ptr<Y> const & r, element_type * p) BOOST_SP_NOEXCEPT: px( p ), pn( r.pn )
+    {
+    }
+
+#if !defined( BOOST_NO_CXX11_RVALUE_REFERENCES )
+
+    template<class Y> weak_ptr(weak_ptr<Y> && r, element_type * p) BOOST_SP_NOEXCEPT: px( p ), pn( std::move( r.pn ) )
+    {
+    }
+
+#endif
+
 #if !defined(BOOST_MSVC) || (BOOST_MSVC >= 1300)
 
     template<class Y>
@@ -194,6 +211,11 @@ public:
         return pn.empty();
     }
 
+    bool empty() const BOOST_SP_NOEXCEPT // extension, not in std::weak_ptr
+    {
+        return pn.empty();
+    }
+
     void reset() BOOST_SP_NOEXCEPT
     {
         this_type().swap(*this);