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+#ifndef BOOST_WEAK_PTR_HPP_INCLUDED
+#define BOOST_WEAK_PTR_HPP_INCLUDED
+
+//
+// weak_ptr.hpp
+//
+// Copyright (c) 2001, 2002, 2003 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/libs/smart_ptr/weak_ptr.htm for documentation.
+//
+
+#include <boost/shared_ptr.hpp>
+
+#ifdef BOOST_MSVC // moved here to work around VC++ compiler crash
+# pragma warning(push)
+# pragma warning(disable:4284) // odd return type for operator->
+#endif
+
+namespace boost
+{
+
+template<class T> class weak_ptr
+{
+private:
+
+ // Borland 5.5.1 specific workarounds
+ typedef weak_ptr<T> this_type;
+
+public:
+
+ typedef T element_type;
+
+ weak_ptr(): px(0), pn() // never throws in 1.30+
+ {
+ }
+
+// generated copy constructor, assignment, destructor are fine
+
+
+//
+// The "obvious" converting constructor implementation:
+//
+// template<class Y>
+// weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+// {
+// }
+//
+// has a serious problem.
+//
+// r.px may already have been invalidated. The px(r.px)
+// conversion may require access to *r.px (virtual inheritance).
+//
+// It is not possible to avoid spurious access violations since
+// in multithreaded programs r.px may be invalidated at any point.
+//
+
+ template<class Y>
+ weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws
+ {
+ px = r.lock().get();
+ }
+
+ template<class Y>
+ weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+ {
+ }
+
+#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
+
+ template<class Y>
+ weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
+ {
+ px = r.lock().get();
+ pn = r.pn;
+ return *this;
+ }
+
+ template<class Y>
+ weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
+ {
+ px = r.px;
+ pn = r.pn;
+ return *this;
+ }
+
+#endif
+
+ shared_ptr<T> lock() const // never throws
+ {
+#if defined(BOOST_HAS_THREADS)
+
+ // optimization: avoid throw overhead
+ if(expired())
+ {
+ return shared_ptr<element_type>();
+ }
+
+ try
+ {
+ return shared_ptr<element_type>(*this);
+ }
+ catch(bad_weak_ptr const &)
+ {
+ // Q: how can we get here?
+ // A: another thread may have invalidated r after the use_count test above.
+ return shared_ptr<element_type>();
+ }
+
+#else
+
+ // optimization: avoid try/catch overhead when single threaded
+ return expired()? shared_ptr<element_type>(): shared_ptr<element_type>(*this);
+
+#endif
+ }
+
+ long use_count() const // never throws
+ {
+ return pn.use_count();
+ }
+
+ bool expired() const // never throws
+ {
+ return pn.use_count() == 0;
+ }
+
+ void reset() // never throws in 1.30+
+ {
+ this_type().swap(*this);
+ }
+
+ void swap(this_type & other) // never throws
+ {
+ std::swap(px, other.px);
+ pn.swap(other.pn);
+ }
+
+ void _internal_assign(T * px2, detail::shared_count const & pn2)
+ {
+ px = px2;
+ pn = pn2;
+ }
+
+ template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const
+ {
+ return pn < rhs.pn;
+ }
+
+// Tasteless as this may seem, making all members public allows member templates
+// to work in the absence of member template friends. (Matthew Langston)
+
+#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
+
+private:
+
+ template<class Y> friend class weak_ptr;
+ template<class Y> friend class shared_ptr;
+
+#endif
+
+ T * px; // contained pointer
+ detail::weak_count pn; // reference counter
+
+}; // weak_ptr
+
+template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
+{
+ return a._internal_less(b);
+}
+
+template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
+{
+ a.swap(b);
+}
+
+// deprecated, provided for backward compatibility
+template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)
+{
+ return r.lock();
+}
+
+} // namespace boost
+
+#ifdef BOOST_MSVC
+# pragma warning(pop)
+#endif
+
+#endif // #ifndef BOOST_WEAK_PTR_HPP_INCLUDED