Structs and method ownership

Obsess over your data structures, not your algorithms. Put behavior on the type it belongs to. Repository, Handler, and Service are names for decisions you haven’t made yet.

Articles: Structs, Method Ownership

You use HashMap every day without caring about its bucket layout. Your job is to build the same thing for your domain: a GpsCoordinates with a distance_to, not twelve copies of the Haversine formula with four f64 parameters each. Every function in utils.rs is a method on a type that does not exist yet, and every UserService is a place where the same rule gets implemented twice.

Five rules: free functions that belong on a type, names that dodge a decision, drawer modules, impls that are three types in a trenchcoat, and parameter lists that are a struct waiting to be named.