Index: base/template_util.h |
diff --git a/base/template_util.h b/base/template_util.h |
index 536cad8f3a3b6f0d77dc7d28076753470d2e90bc..874b8ea508070d9fb46e64bc178a81fe65bb76df 100644 |
--- a/base/template_util.h |
+++ b/base/template_util.h |
@@ -42,6 +42,19 @@ template <class T> struct is_non_const_reference<const T&> : std::false_type {}; |
namespace internal { |
+template <typename...> |
+struct make_void { |
+ using type = void; |
+}; |
+ |
+// A clone of C++17 std::void_t. |
+// Unlike the original version, we need |make_void| as a helper struct to avoid |
+// a C++14 defect. |
+// ref: http://en.cppreference.com/w/cpp/types/void_t |
+// ref: http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558 |
+template <typename... Ts> |
+using void_t = typename make_void<Ts...>::type; |
+ |
// Uses expression SFINAE to detect whether using operator<< would work. |
template <typename T, typename = void> |
struct SupportsOstreamOperator : std::false_type {}; |