[cleanup] Use enable_if_t and result_of_t from std::

dune/solvers/solvers/criterion.hh

@@ -7,6 +7,7 @@
 #include <string>
 #include <tuple>
 #include <memory>
+#include <type_traits>
 
 #include <dune/common/stringutility.hh>
 
@@ -28,12 +29,6 @@ namespace Dune {
      */
     class Criterion
     {
-      template <typename F>
-      using result_of_t = typename std::result_of<F>::type;
-
-      template <bool Condition, typename T=void>
-      using enable_if_t = typename std::enable_if<Condition, T>::type;
-
       typedef std::tuple<bool, std::string> Result;
 
     public:
@@ -56,7 +51,7 @@ namespace Dune {
        * of the header string coincide to get a readable log.
        */
       template<class F,
-        enable_if_t<std::is_convertible<result_of_t<F()>, Result>::value, int> = 0>
+        std::enable_if_t<std::is_convertible<std::result_of_t<F()>, Result>::value, int> = 0>
       Criterion(F&& f, const std::string& header) :
         f_(std::forward<F>(f)),
         header_(header)
@@ -80,7 +75,7 @@ namespace Dune {
        * of the header string coincide to get a readable log.
        */
       template<class F,
-        enable_if_t<std::is_convertible<result_of_t<F()>, std::string>::value, int> = 0>
+        std::enable_if_t<std::is_convertible<std::result_of_t<F()>, std::string>::value, int> = 0>
       Criterion(F&& f, const std::string& header) :
         f_( [=]() {return std::make_tuple(false, f());} ),
         header_(header)