A detail of the hash protocol

[bearophile]

In this page:
http://www.digitalmars.com/d/1.0/arrays.html#associative
regarding the hashing protocol it says that structs need:
uint toHash();
While classes:
hash_t toHash()

Is that a little documentation error? I presume they both have to return an uint or hash_t or a size_t...

What's the purpose of a separated hash_t type? Can't it be removed, keeping just an uint or size_t for that purpose?

Thank you, bye,
bearophile