Index: uspace/lib/cpp/include/internal/hash_table.hpp
===================================================================
--- uspace/lib/cpp/include/internal/hash_table.hpp	(revision 7a66678916923f4cfb6437cb2d864d75526b735f)
+++ uspace/lib/cpp/include/internal/hash_table.hpp	(revision 875788a8f6a9a1d32b9cfd23a37541171cc0b146)
@@ -57,4 +57,9 @@
             return p.first;
         }
+
+        const Key& operator()(pair<const Key, Value>& p) const noexcept
+        {
+            return p.first;
+        }
     };
 
@@ -63,4 +68,9 @@
     {
         Key& operator()(Key& k) const noexcept
+        {
+            return k;
+        }
+
+        const Key& operator()(const Key& k) const noexcept
         {
             return k;
@@ -1078,4 +1088,9 @@
             }
 
+            const key_type& get_key(const value_type& val)
+            {
+                return key_extractor_(val);
+            }
+
         /* private: */
             hash_table_bucket<value_type, size_type>* table_;