#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 <memory> // boost.TR1 include order fix

#include <boost/detail/shared_count.hpp>

#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 >= 1300)

    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, boost::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

    boost::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