externals: Update boost to 1.72 and add Boost Context

boost/smart_ptr/enable_shared_from_this.hpp

@@ -0,0 +1,90 @@
+#ifndef BOOST_SMART_PTR_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED
+#define BOOST_SMART_PTR_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED
+
+//
+//  enable_shared_from_this.hpp
+//
+//  Copyright 2002, 2009 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/ for documentation.
+//
+
+#include <boost/smart_ptr/weak_ptr.hpp>
+#include <boost/smart_ptr/shared_ptr.hpp>
+#include <boost/smart_ptr/detail/sp_noexcept.hpp>
+#include <boost/assert.hpp>
+#include <boost/config.hpp>
+
+namespace boost
+{
+
+template<class T> class enable_shared_from_this
+{
+protected:
+
+    BOOST_CONSTEXPR enable_shared_from_this() BOOST_SP_NOEXCEPT
+    {
+    }
+
+    BOOST_CONSTEXPR enable_shared_from_this(enable_shared_from_this const &) BOOST_SP_NOEXCEPT
+    {
+    }
+
+    enable_shared_from_this & operator=(enable_shared_from_this const &) BOOST_SP_NOEXCEPT
+    {
+        return *this;
+    }
+
+    ~enable_shared_from_this() BOOST_SP_NOEXCEPT // ~weak_ptr<T> newer throws, so this call also must not throw
+    {
+    }
+
+public:
+
+    shared_ptr<T> shared_from_this()
+    {
+        shared_ptr<T> p( weak_this_ );
+        BOOST_ASSERT( p.get() == this );
+        return p;
+    }
+
+    shared_ptr<T const> shared_from_this() const
+    {
+        shared_ptr<T const> p( weak_this_ );
+        BOOST_ASSERT( p.get() == this );
+        return p;
+    }
+
+    weak_ptr<T> weak_from_this() BOOST_SP_NOEXCEPT
+    {
+        return weak_this_;
+    }
+
+    weak_ptr<T const> weak_from_this() const BOOST_SP_NOEXCEPT
+    {
+        return weak_this_;
+    }
+
+public: // actually private, but avoids compiler template friendship issues
+
+    // Note: invoked automatically by shared_ptr; do not call
+    template<class X, class Y> void _internal_accept_owner( shared_ptr<X> const * ppx, Y * py ) const BOOST_SP_NOEXCEPT
+    {
+        if( weak_this_.expired() )
+        {
+            weak_this_ = shared_ptr<T>( *ppx, py );
+        }
+    }
+
+private:
+
+    mutable weak_ptr<T> weak_this_;
+};
+
+} // namespace boost
+
+#endif  // #ifndef BOOST_SMART_PTR_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED