fixed init_type machinery

include/boost/unordered/detail/foa.hpp

@@ -828,12 +828,14 @@ table:empty_value<Hash,0>,empty_value<Pred,1>,empty_value<Allocator,1>
 
 public:
   using key_type=typename type_policy::key_type;
-  using init_type=typename type_policy::value_type;
+  using init_type=typename type_policy::init_type;
   using value_type=typename type_policy::value_type;
 
 private:
   static constexpr bool has_mutable_iterator=
     !std::is_same<key_type,value_type>::value;
+  static constexpr bool has_different_init_type=
+    !std::is_same<init_type,value_type>::value;
 
 public:
   using hasher=Hash;
@@ -1207,6 +1209,17 @@ private:
     }
   }
 
+  template<
+    bool dependent_value=false,
+    typename std::enable_if<
+      has_different_init_type||dependent_value>::type* =nullptr
+  >
+  static inline auto key_from(const init_type& x)
+    ->decltype(type_policy::extract(x))
+  {
+    return type_policy::extract(x);
+  }
+
   static inline auto key_from(const value_type& x)
     ->decltype(type_policy::extract(x))
   {

include/boost/unordered/unordered_flat_map.hpp

@@ -30,6 +30,7 @@ namespace boost {
         using key_type = Key;
         using init_type = std::pair<Key, T>;
         using value_type = std::pair<Key const, T>;
+        static Key const& extract(init_type const& kv) { return kv.first; }
         static Key const& extract(value_type const& kv) { return kv.first; }
 
         template<typename F>