HashMap's docs can do a better job of explaining how to implement a hasher

[steveklabnik]

The docs say:

The hashing algorithm can be replaced on a per-HashMap basis using the default, with_hasher, and with_capacity_and_hasher methods. Many alternative algorithms are available on crates.io, such as the fnv crate.

However, there isn't a mention of the Hasher trait. If you look at the docs for with_hasher, the type is just S. If you look at the struct definition, S = RandomState is all you get. You have to click to RandomState, and then see that it implements Hasher, to know what's going on.