Serialization of dense_hash_map

Hi, any plan for this?

> In addition to the normal hash-map operations, sparse_hash_map can
> read and write hashtables to disk.  (dense_hash_map also has the API,
> but it has not yet been implemented, and writes will always fail.)

https://github.com/sparsehash/sparsehash-c11/blob/master/README#L85

How can I serialize / deserialize a dense_hash_map in a fast way?
Thanks.