What I'm going to describe is just derived from how traits themselvces work, but despite having now written a decent amount of Rust, I had not really fully absorbed this fact.

Imagine you are working with some cell towers owned by various people, in various locations:

struct CellTower {
    id: String;
    location: Location;
    owner_id: String;

You might want to do various things with these so you can add an impl block with some helper functions to help make your code legible.

impl CellTower {
  fn distance_from(&self, point: Location): Distance {
     return self.location.distance(point)

This lets you do stuff like cell_tower.distance_from(my_house) and other "normal" programming with objects that we're all used to. It is not really different from something like

distance_from(cell_tower, my_house)

But aesthetics really do matter.

You heard about fluent interfaces and want that! You want nice method chaining.

In Python and friends, my strategy might be to create a wrapped container class and build an interface with that.

But here with Rust we actually can totally circumvent this and add extra functionality to existing data structures:

trait FilterableTowerContainer {
  fn owned_by(self, owner_id: String) -> Self
  fn close_to(self, location: Location) -> Self

impl FilterableTowerContainer for Vec<CellTower> {
  fn owned_by(self, owner_id: String) -> Self {
  fn close_to(self, location: Location) -> Self {

fn main() {
    let towers : Vec<CellTower> = ...;
    let my_home: Location = ...;
    let my_favorite_company = ...;
    let usable_towers = towers
      "Number of found usable towers: {}",

The interesting bit here being:

let usable_towers = towers

Despite me not having written Vec's implementation, I'm able to "add more methods" to it.

This is all just really how all traits work, but if you're coming from a "objects are instances of classes and have a specificied MRO" world it's very magical!

And it saves you from writing things like:

let usable_towers = owned_by(
  close_to(my_towers, my_home),

I'll leave more cursed trait implementation ideas as an exercise to the reader.

Update: the term of art for this in Rust is Extension Traits.