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base/template_util.h

Index: base/template_util.h
diff --git a/base/template_util.h b/base/template_util.h
index 1bfc1ac814a23ceb186a9fcf6fa5924281d92783..af4cdd5a21c4993dca662b7c717dfcc25b7f1714 100644
--- a/base/template_util.h
+++ b/base/template_util.h
@@ -29,6 +29,20 @@ template <class T> struct is_non_const_reference : std::false_type {};
 template <class T> struct is_non_const_reference<T&> : std::true_type {};
 template <class T> struct is_non_const_reference<const T&> : std::false_type {};
 
+// underlying_number
+// Casts an enum to its underlying integral type, leaves other numbers alone.
+// Useful for scoped enums, which don't cast implicitly.
+template <typename T,
+          typename std::enable_if<std::is_enum<T>::value, int>::type = 0>
+constexpr typename std::underlying_type<T>::type underlying_number(T val) {
+  return static_cast<typename std::underlying_type<T>::type>(val);
+}
+template <typename T,
+          typename std::enable_if<std::is_arithmetic<T>::value, int>::type = 0>
+constexpr T underlying_number(T val) {
+  return val;
+}
+
 // is_assignable
 
 namespace internal {