Rust is doing something even more subtle here than just making the hash function a container property. There are two inter-related Rust traits, Hash is a trait which types implement to explain abstractly how to hash that type, but it's written in terms of a Hasher trait so you can drop in a different function with the same API. The Rust standard library provides a derive macro for Hash, so most people can just gesture vaguely at their custom type and have it hashed correctly for any hash functions they need. The naïve approach here easily ends up doing a bad job either colliding hashes for correlated objects in a surprising way or emitting different hashes for equivalent objects because people who make a user defined type probably aren't hashing experts.