improved SFINAE in type_caster_generic (closes #70)

include/pybind11/cast.h

@@ -209,11 +209,11 @@ public:
     operator type*() { return (type *) value; }
     operator type&() { return *((type *) value); }
 protected:
-    template <typename T = type, typename std::enable_if<std::is_copy_constructible<T>::value, int>::type = 0>
+    template <typename T = type, typename std::enable_if<detail::is_copy_constructible<T>::value, int>::type = 0>
     static void *copy_constructor(const void *arg) {
         return new type(*((const type *) arg));
     }
-    template <typename T = type, typename std::enable_if<!std::is_copy_constructible<T>::value, int>::type = 0>
+    template <typename T = type, typename std::enable_if<!detail::is_copy_constructible<T>::value, int>::type = 0>
     static void *copy_constructor(const void *) { return nullptr; }
 };
 

include/pybind11/common.h

@@ -240,6 +240,14 @@ template <typename T> struct intrinsic_type<T&&>                  { typedef type
 template <typename T, size_t N> struct intrinsic_type<const T[N]> { typedef typename intrinsic_type<T>::type type; };
 template <typename T, size_t N> struct intrinsic_type<T[N]>       { typedef typename intrinsic_type<T>::type type; };
 
+/** \brief SFINAE helper class to check if a copy constructor is usable (in contrast to 
+ * std::is_copy_constructible, this class also checks if the 'new' operator is accessible */
+template <typename T>  struct is_copy_constructible {
+    template <typename T2> static std::true_type test(decltype(new T2(std::declval<T2>())) *);
+    template <typename T2> static std::false_type test(...);
+    static const bool value = std::is_same<std::true_type, decltype(test<T>(nullptr))>::value;
+};
+
 /// Helper type to replace 'void' in some expressions
 struct void_type { };