Length traits in Rust

length.rs

use std::ops::{Add, AddAssign, Mul};

#[derive(Debug)]
struct Millimeters<T>(T);

struct Centimeters<T>(Millimeters<T>);

struct Meters<T>(Millimeters<T>);

/// Length represents a length in millimeters
trait Length<T> {
    fn new(x: T) -> Self;
}

impl<T> Length<T> for Millimeters<T> {
    fn new(x: T) -> Millimeters<T> {
        Millimeters(x)
    }
}

impl<T> Length<T> for Centimeters<T>
where
    T: Mul<u64, Output = T>,
{
    fn new(x: T) -> Centimeters<T> {
        Centimeters(Millimeters(x * 10))
    }
}

impl<T> Length<T> for Meters<T>
where
    T: Mul<u64, Output = T>,
{
    fn new(x: T) -> Meters<T> {
        Meters(Millimeters(x * 1000))
    }
}

impl<T> Add for Millimeters<T>
where
    T: Add<Output = T>,
{
    type Output = Self;

    fn add(self, other: Self) -> Self {
        Self(self.0 + other.0)
    }
}

impl<T> Add<Centimeters<T>> for Millimeters<T>
where
    T: Add<Output = T>,
{
    type Output = Millimeters<T>;

    fn add(self, other: Centimeters<T>) -> Self::Output {
        let mm = other.0;
        Self(self.0 + mm.0)
    }
}

impl<T> Add<Meters<T>> for Millimeters<T>
where
    T: Add<Output = T>,
{
    type Output = Millimeters<T>;

    fn add(self, other: Meters<T>) -> Self::Output {
        let mm = other.0;
        Self(self.0 + mm.0)
    }
}

impl<T> AddAssign for Millimeters<T>
where
    T: Add<Output = T> + Copy,
{
    fn add_assign(&mut self, other: Self) {
        *self = Self(self.0 + other.0);
    }
}

impl<T> AddAssign<Centimeters<T>> for Millimeters<T>
where
    T: Add<Output = T> + Copy,
{
    fn add_assign(&mut self, other: Centimeters<T>) {
        let mm = other.0;
        *self = Self(self.0 + mm.0);
    }
}

impl<T> AddAssign<Meters<T>> for Millimeters<T>
where
    T: Add<Output = T> + Copy,
{
    fn add_assign(&mut self, other: Meters<T>) {
        let mm = other.0;
        *self = Self(self.0 + mm.0);
    }
}

fn main() {
    let mut d = Millimeters::new(1000);
    d = d + Millimeters::new(100);
    d += Centimeters::new(10);
    d += Meters::new(1);
    println!("{:?}", d)
}