Composition over Inheritance

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

pub struct Uuid([u8; 16]);

pub struct Address {
    street: String,
    city_or_province: String,
    code: String,
    country: String,
}

pub struct User {
    id: Uuid,
    address: Address,
}

Rather than mixins or inheritance, we compose types by creating fields of different types.

This has downsides, largely in ergonomics of field access, but gives developers a lot of control and clarity over what a type does and it has access to.
When deriving traits, make sure all the field types of a struct or variant types of an enum implement that trait. Derive macros often assume all types that compose a new type implement that trait already.