Functor updating ranks of entries.
| Parameter | Description | Default Value | 
| Key | Key type. | - | 
| Allocator | Allocator type. The allocator is only used for definitions, e.g., size_type, pointer, and reference. | std::allocator<char> | 
| Type | Definition | Description | 
| allocator | Allocator | Allocator type. | 
| Type | Definition | Description | 
| key_type | order_statistics_key<
    Key,
    Allocator> | Key-type on which this functor operates. | 
| const_key_pointer | typename Allocator::template rebind< key_type>::other::const_pointer | Key pointer-type on which this functor operates. | 
| Method | Description | 
| inline void swap (order_statistics_node_updator &r_other) | Swaps content. | 
| inline void operator() (const_key_pointer p_key, const_key_pointer p_l_child_key, const_key_pointer p_r_child_key) | Updates the rank of a key given its child keys. |