/** Swap the content of two cache_set.
*
* @param other another cache_set
*/
void swap( cache_set& other ) { m_ht.swap( other.m_ht ); }
/** Swap the content of two cache_map.
*
* @param other another cache_map
*/
void swap( cache_map& other ) { m_ht.swap( other.m_ht ); }