cpplearner
diff --git a/‎is_reference_wrapper.hpp‎
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+#pragma once
+
+#include <functional>
+
+// A type can specialize this template if it wants itself to be treated like
+// a std::reference_wrapper. E.g. a replacement of std::reference_wrapper that
+// supports constexpr operations may want to specialize this template.
+template <class T>
+struct is_reference_wrapper : std::false_type {};
+template <class U>
+struct is_reference_wrapper<std::reference_wrapper<U>> : std::true_type {};
+template <class T>
+constexpr bool is_reference_wrapper_v = is_reference_wrapper<T>::value;