value constructor is sfinae-friendly

doc/91_relnotes.qbk

@@ -20,6 +20,7 @@
   * you can swap optional references: it is like swapping pointers: shalow, underlying objects are not affected,
   * optional references to abstract types work.
 * Documented nested typedefs ([@https://svn.boost.org/trac/boost/ticket/5193 Trac #5193]).
+* Made the optional value constructor SFINAE-friendly, which fixes [@https://svn.boost.org/trac/boost/ticket/12002 Trac #12002].
 
 [heading Boost Release 1.60]
 

doc/html/boost_optional/relnotes.html

@@ -60,6 +60,9 @@
           Documented nested typedefs (<a href="https://svn.boost.org/trac/boost/ticket/5193" target="_top">Trac
           #5193</a>).
         </li>
+<li class="listitem">
+          Made the optional value constructor SFINAE-friendly, which fixes <a href="https://svn.boost.org/trac/boost/ticket/12002" target="_top">Trac #12002</a>.
+        </li>
 </ul></div>
 <h4>
 <a name="boost_optional.relnotes.h1"></a>

doc/html/index.html

@@ -144,7 +144,7 @@
 </div>
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
-<td align="left"><p><small>Last revised: February 18, 2016 at 23:24:54 GMT</small></p></td>
+<td align="left"><p><small>Last revised: February 19, 2016 at 17:38:50 GMT</small></p></td>
 <td align="right"><div class="copyright-footer"></div></td>
 </tr></table>
 <hr>

include/boost/optional/optional.hpp

@@ -37,6 +37,7 @@
 #include <boost/type_traits/remove_reference.hpp>
 #include <boost/type_traits/decay.hpp>
 #include <boost/type_traits/is_base_of.hpp>
+#include <boost/type_traits/is_constructible.hpp>
 #include <boost/type_traits/is_lvalue_reference.hpp>
 #include <boost/type_traits/is_nothrow_move_assignable.hpp>
 #include <boost/type_traits/is_nothrow_move_constructible.hpp>
@@ -565,17 +566,39 @@ class optional_base : public optional_tag
     storage_type m_storage ;
 } ;
 
-
+// definition of metafunciton is_optional_val_init_candidate
 template <typename U>
 struct is_optional_related
-  : boost::conditional<boost::is_base_of<optional_detail::optional_tag, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
+  : boost::conditional< boost::is_base_of<optional_detail::optional_tag, BOOST_DEDUCED_TYPENAME boost::decay<U>::type>::value
-                    || boost::is_same<BOOST_DEDUCED_TYPENAME boost::decay<U>::type, none_t>::value,
+                     || boost::is_same<BOOST_DEDUCED_TYPENAME boost::decay<U>::type, none_t>::value,
     boost::true_type, boost::false_type>::type
 {};
-    
+
-template <typename, typename U>
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) && !defined(BOOST_NO_CXX11_DECLTYPE) && !BOOST_WORKAROUND(BOOST_MSVC, < 1800) && !BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40500)
+  // this condition is a copy paste from is_constructible.hpp
+  
+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::true_type, boost::false_type>::type
+{};
+
+#else
+
+#define BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT
+
+template <typename, typename>
+struct is_convertible_to_T_or_factory : boost::true_type
+{};
+
+#endif // is_convertible condition
+
+template <typename T, typename U>
 struct is_optional_val_init_candidate
-  : boost::conditional<!is_optional_related<U>::value, boost::true_type, boost::false_type>::type
+  : boost::conditional< !is_optional_related<U>::value && is_convertible_to_T_or_factory<T, U>::value
+                      , boost::true_type, boost::false_type>::type
 {};
     
 } // namespace optional_detail

test/Jamfile.v2

@@ -39,6 +39,7 @@ import testing ;
     [ run optional_test_emplace.cpp ]
     [ run optional_test_minimum_requirements.cpp ]
     [ run optional_test_msvc_bug_workaround.cpp ]
+    [ compile optional_test_sfinae_friendly_value_ctor.cpp ]
     [ compile-fail optional_test_ref_convert_assign_const_int_prevented.cpp ]
     [ compile-fail optional_test_fail1.cpp ]
     [ compile-fail optional_test_fail3a.cpp ]

test/optional_test_sfinae_friendly_value_ctor.cpp

@@ -0,0 +1,38 @@
+// Copyright (C) 2014 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
+
+using boost::optional;
+
+#if (!defined BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT)
+
+struct X {};
+struct Y {};
+  
+struct Resource
+{
+  explicit Resource(const X&) {}
+};
+
+BOOST_STATIC_ASSERT(( boost::is_constructible<Resource, const X&>::value));
+BOOST_STATIC_ASSERT((!boost::is_constructible<Resource, const Y&>::value));
+
+BOOST_STATIC_ASSERT(( boost::is_constructible<optional<Resource>, const X&>::value));
+BOOST_STATIC_ASSERT((!boost::is_constructible<optional<Resource>, const Y&>::value));
+  
+#endif
+
+int main() { }