TypeScript Option/Maybe type

maybe.ts

export class Some<T> {
    public some: true = true;
    constructor(public value: T) { }
}

export class None {
    public some: false = false;
}

export type Maybe<T> = Some<T> | None;

sample-maybe-usage.ts

import { Maybe, None, Some } from "./maybe";

function safeParseInt(val: string): Maybe<number> {
    const num = parseInt(val, 10);
    if (isNaN(num)) {
        // Can also return { some: false } here.
        return new None();
    }

    return new Some(num);
}

function displayInt(val: string) {
    const result = safeParseInt(val);
    if (result.some) {
        // With the above type guard, `result` is `Some<int>` here.
        console.log(result.value);
    } else {
        // The `result` object is `None` here.
        console.error("Value is not a number.");
    }
}

Inspired by Josh Wulf

If line 7 of the None type is changed to public some?: false = false;, then {} also becomes equivalent to None. This can make it cleaner and more elegant to return None, but it changes the types of checks that one can perform on Maybe results. For example if (result.some === true) is still valid, but the converse check for false isn't.