Use explicit operator bool when available; add nullptr support to shared_ptr. Refs #4116.

[SVN r81780]

include/boost/smart_ptr/scoped_ptr.hpp

@@ -11,6 +11,7 @@
 //  http://www.boost.org/libs/smart_ptr/scoped_ptr.htm
 //
 
+#include <boost/config.hpp>
 #include <boost/assert.hpp>
 #include <boost/checked_delete.hpp>
 #include <boost/detail/workaround.hpp>
@@ -114,6 +115,30 @@ public:
     }
 };
 
+#if !defined( BOOST_NO_CXX11_NULLPTR )
+
+template<class T> inline bool operator==( scoped_ptr<T> const & p, std::nullptr_t ) BOOST_NOEXCEPT
+{
+    return p.get() == 0;
+}
+
+template<class T> inline bool operator==( std::nullptr_t, scoped_ptr<T> const & p ) BOOST_NOEXCEPT
+{
+    return p.get() == 0;
+}
+
+template<class T> inline bool operator!=( scoped_ptr<T> const & p, std::nullptr_t ) BOOST_NOEXCEPT
+{
+    return p.get() != 0;
+}
+
+template<class T> inline bool operator!=( std::nullptr_t, scoped_ptr<T> const & p ) BOOST_NOEXCEPT
+{
+    return p.get() != 0;
+}
+
+#endif
+
 template<class T> inline void swap(scoped_ptr<T> & a, scoped_ptr<T> & b) BOOST_NOEXCEPT
 {
     a.swap(b);