Phantom Type - 2

pt-2.ts

class Temp<A> {
    private readonly __unit__: A; // structural diff used here
    constructor(degree: number) { }
}

interface Celcius { __celcius__: never } // structural diff
interface Fahrenheit { __fahrenheit__: never } // structural diff

const isBoiling = (temp: Temp<Celcius>) => temp.degree >= 100;

const c100 = new Temp<Celcius>(100);
const f100 = new Temp<Fahrenheit>(100);

isBoiling(c100); // type-check!
isBoiling(f100); // error!