Implemented reset syntax: o = {}

include/boost/optional/optional.hpp

@@ -741,7 +741,7 @@ template <typename T, typename U>
 struct is_convertible_to_T_or_factory
   : boost::conditional< boost::is_base_of<boost::in_place_factory_base, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
                      || boost::is_base_of<boost::typed_in_place_factory_base, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
-                     || boost::is_constructible<T, U&&>::value
+                     || (boost::is_constructible<T, U&&>::value && !boost::is_same<T, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value)
                       , boost::true_type, boost::false_type>::type
 {};
 
@@ -954,6 +954,19 @@ class optional : public optional_detail::optional_base<T>
       }
 #endif
 
+
+#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+
+    // Assigns from a T (deep-moves/copies the rhs value)
+    template <typename T_>
+    BOOST_DEDUCED_TYPENAME boost::enable_if<boost::is_same<T, BOOST_DEDUCED_TYPENAME boost::decay<T_>::type>, optional&>::type
+    operator= ( T_&& val )
+      {
+        this->assign( boost::forward<T_>(val) ) ;
+        return *this ;
+      }
+#else
+
     // Assigns from a T (deep-copies the rhs value)
     // Basic Guarantee: If T::( T const& ) throws, this is left UNINITIALIZED
     optional& operator= ( argument_type val )
@@ -962,13 +975,6 @@ class optional : public optional_detail::optional_base<T>
         return *this ;
       }
       
-#ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
-    // Assigns from a T (deep-moves the rhs value)
-    optional& operator= ( rval_reference_type val )
-      {
-        this->assign( boost::move(val) ) ;
-        return *this ;
-      }
 #endif
       
     // Assigns from a "none"

test/Jamfile.v2

@@ -21,6 +21,7 @@ import testing ;
     [ run optional_test_swap.cpp ]
     [ run optional_test_conversions_from_U.cpp ]
     [ run optional_test_convert_from_T.cpp ]
+    [ run optional_test_empty_braces.cpp ]
     [ run optional_test_tie.cpp ]
     [ run optional_test_ref_assign_portable_minimum.cpp ]
     [ run optional_test_ref_assign_mutable_int.cpp ]

test/optional_test_empty_braces.cpp

@@ -0,0 +1,57 @@
+// Copyright (C) 2016 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to 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/lib/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#include "boost/optional/optional.hpp"
+
+#ifdef __BORLANDC__
+#pragma hdrstop
+#endif
+
+#include "boost/core/lightweight_test.hpp"
+
+//#ifndef BOOST_OPTIONAL_NO_CONVERTING_ASSIGNMENT
+//#ifndef BOOST_OPTIONAL_NO_CONVERTING_COPY_CTOR
+
+using boost::optional;
+
+struct Value
+{
+  explicit Value(int) {}
+};
+
+#ifndef BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX
+template <typename T>
+void test_brace_init()
+{
+  optional<T> o = {};
+  BOOST_TEST(!o);
+}
+
+template <typename T>
+void test_brace_assign()
+{
+  optional<T> o;
+  o = {};
+  BOOST_TEST(!o);
+} 
+#endif
+
+int main()
+{
+#ifndef BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX
+  test_brace_init<int>();
+  test_brace_init<Value>();
+  test_brace_assign<int>();
+  test_brace_assign<Value>();
+#endif
+
+  return boost::report_errors();
+}