Implement merge

include/boost/unordered/detail/implementation.hpp

@@ -3840,6 +3840,30 @@ struct table_impl : boost::unordered::detail::table<Types>
         return iterator(pos);
     }
 
+    template <typename Types2> void merge_impl(table_impl<Types2>& other)
+    {
+        if (other.size_) {
+            link_pointer prev = other.get_previous_start();
+
+            while (prev->next_) {
+                node_pointer n = other.next_node(prev);
+                const_key_type& k = this->get_key(n->value());
+                std::size_t key_hash = this->hash(k);
+                node_pointer pos = this->find_node(key_hash, k);
+
+                if (pos) {
+                    prev = n;
+                } else {
+                    this->reserve_for_insert(this->size_ + 1);
+                    prev->next_ = n->next_;
+                    --other.size_;
+                    other.fix_bucket(other.hash_to_bucket(n->hash_), prev);
+                    this->add_node(n, key_hash);
+                }
+            }
+        }
+    }
+
     ////////////////////////////////////////////////////////////////////////
     // Insert range methods
     //