Index: uspace/lib/cpp/include/impl/functional.hpp
===================================================================
--- uspace/lib/cpp/include/impl/functional.hpp	(revision 72f5379ef7851d78d619e125652ce7766d7ca0ae)
+++ uspace/lib/cpp/include/impl/functional.hpp	(revision 2c223a9d6407528bbeeb3483ace1cbe678a671ab)
@@ -786,7 +786,31 @@
      */
 
-    // TODO: void should be /unspecified/
+    namespace aux
+    {
+        template<class F>
+        class mem_fn_t
+        {
+            // TODO: conditional typedefs
+            public:
+                mem_fn_t(F f)
+                    : func_{f}
+                { /* DUMMY BODY */ }
+
+                template<class... Args>
+                decltype(auto) operator()(Args&&... args)
+                {
+                    return invoke(func_, forward<Args>(args)...);
+                }
+
+            private:
+                F func_;
+        };
+    }
+
     template<class R, class T>
-    void mem_fn(R T::* f);
+    aux::mem_fn_t<R T::*> mem_fn(R T::* f)
+    {
+        return aux::mem_fn_t<R T::*>{f};
+    }
 
     /**