Session 7: Private Class Members And Nominal Typing

[JamieB-gu]

We should probably mention in the session that the moment you create a private member in a class, you effectively achieve Nominal typing in TypeScript!

Suggested here:

#40 (review)

[mxdvl]

class Named {
    #name: string;
    constructor(name: string) {
        this.#name = name;
    }

    get name() { return this.#name }
}

class Person {
    #name: string; // this is sufficient to create incompatible classes
    job: string;
    constructor(name: string, job: string) {
        this.#name = name;
        this.job = job;
    }

    get name() { return this.#name }
}

const cpScott = new Person('CP Scott', 'Journalist',);

const hello = (named: Named): string =>
    `Hello ${named.name}`;

const helloCPScott = hello(cpScott);
// Argument of type 'Person' is not assignable to parameter of type 'Named'.
//  Property '#name' in type 'Person' refers to a different member that cannot be accessed from within type 'Named'.(2345)