Use std::enable_if in detail/enable_if.hpp

include/boost/system/detail/enable_if.hpp

@@ -5,28 +5,19 @@
 // Distributed under the Boost Software License, Version 1.0
 // http://www.boost.org/LICENSE_1_0.txt
 
+#include <type_traits>
+
 namespace boost
 {
-
 namespace system
 {
-
 namespace detail
 {
 
-template<bool C, class T = void> struct enable_if
-{
-    typedef T type;
-};
-
-template<class T> struct enable_if<false, T>
-{
-};
+using std::enable_if;
 
 } // namespace detail
-
 } // namespace system
-
 } // namespace boost
 
 #endif // #ifndef BOOST_SYSTEM_DETAIL_ENABLE_IF_HPP_INCLUDED