Branded types for TypeScript • Hacker News Board

Re: Branded types for TypeScript

#141

Post by jacobsimon » Thu, May 16, 2024, 2:12 PM UTC

brlewis wrote: post #51

jacobsimon wrote: post #44

Earlier quoted context omitted.

You can still do this with classes in typescript: class Hash extends String {} https://www.typescriptlang.org/play/?#code/MYGwhgzhAEASkAtoF...

That's distinguishing the String class from primitive string. I don't think that would still work with another `extends String` the same shape as Hash. For example: https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABO... class Animal { isJaguar: boolean = false; } class Automobile { isJaguar: boolean = false; } function engineSound(car: Automobile) { return car.isJaguar ? "vroom" : "put put"; } console.log(en…

Oops you’re right!

Re: Branded types for TypeScript

#142

Post by AlienRobot » Thu, May 16, 2024, 2:12 PM UTC

conaclos wrote: post #116

I don't understand why users of branded types use strings as brands. Also using a utility type makes unreadable the TypeScript errors related to this type. If I had to use branded types, I personally would prefer a different approach: declare const USER_BRAND: unique symbol type User = { name: string, [USER_BRAND]: undefined } This also allows subtyping: declare const PERSON_BRAND: unique symbol type Person = { name:…

iirc this is why the hungarian notation existed. They had ints for columns and rows and they used a prefix on variable names to distinguish which ints were columns and which ints were rows. Though I may be misremembering.

Re: Branded types for TypeScript

#143

Post by stiiv » Thu, May 16, 2024, 2:15 PM UTC

tom_ wrote: post #75

stiiv wrote: post #38

Earlier quoted context omitted.

> A runtime bug is now a compile time bug. This isn't valuable to you? How do you get this without nominal typing, especially of primatives?

Did they edit their post? The > syntax indicates a verbatim quote here.

Verbatim from OP.

Re: Branded types for TypeScript

#144

Post by stiiv » Thu, May 16, 2024, 2:21 PM UTC

mattstir wrote: post #99

stiiv wrote: post #37

As someone who values a tight domain model (a la DDD) and primarily writes TypeScript, I've considered introducing branded types many times, and always decline. Instead, we just opt for "aliases," especially of primatives (`type NonEmptyString = string`), and live with the consequences. The main consequence is that we need an extra level of vigilance and discipline in PR reviews, or else implicit trust in one another…

> The other implementation is detailed in this article, and requires the addition of unique field value to objects. That's not quite what ends up happening in this article though. The actual objects themselves are left unchanged (no new fields added), but you're telling the compiler that the value is actually an intersection type with that unique field. There a load-bearing `as Hash` in the return statement of `gener…

Big thank you for clarifying -- I missed that. This approach is far less unsavory that some other attempts that I've seen.

Re: Branded types for TypeScript

#145

Post by arctek » Thu, May 16, 2024, 2:39 PM UTC

kaoD wrote: post #60

msoad wrote: post #21

It took me so long to fully appreciate TypeScript's design decision for doing structural typing vs. nominal typing. In all scenarios, including the "issue" highlighted in this article there is no reason for wanting nominal typing. In this case where the wrong order of parameters was the issue, you can solve it with [Template Literal Types]( https://www.typescriptlang.org/docs/handbook/2/template-lite... ). See [1]. A…

> In all scenarios [...] there is no reason for wanting nominal typing. Hard disagree. It's very useful to e.g. make a `PasswordResetToken` be different from a `CsrfToken`. Prepending a template literal changes the underlying value and you can no longer do stuff like `Buffer.from(token, 'base64')`. It's just a poor-man's version of branding with all the disadvantages and none of the advantages. You can still `hash.to…

Thanks for the examples, I'm working on a TypeScript code base at the moment and this is fantastic way of adding compile-time typing across many of the basic types I'm using!

Re: Branded types for TypeScript

#146

Post by morning4coffe » Thu, May 16, 2024, 3:41 PM UTC

Interesting approach to simulate nominal typing in TypeScript. It's like finding creative solutions to bridge the gap between structural and nominal typing. Nicely explained in the article!

Re: Branded types for TypeScript

#147

Post by tom_ » Thu, May 16, 2024, 3:49 PM UTC

stiiv wrote: post #143

tom_ wrote: post #75

Earlier quoted context omitted.

Did they edit their post? The > syntax indicates a verbatim quote here.

Verbatim from OP.

Oh, I see, it's from the article - right, got it.

Re: Branded types for TypeScript

#148

Post by vjerancrnjak » Thu, May 16, 2024, 6:13 PM UTC

Quothling wrote: post #132

vjerancrnjak wrote: post #125

Earlier quoted context omitted.

One tricky scenario I stumbled on is `.toString()`. Everything has a `.toString()` but some objects A have `.toString(arg1, arg2, arg3)`. But replacing A with something that does not have toString with arguments still type checks, yet will probably result in serious error.

This is sort of by design. Generally speaking Object.prototype.toString() does not accept parameters, I think the only "standard" implementation which takes parameters is Number.prototype.toString(). You can overwrite .toString with your customized functions, but doing so is full of risks which can basiclaly be summed up to performance overhead and unexpected behaviour due to how you're not really in control of an ob…

node's Buffer has a `toString` with arguments (probably should have been called encode).

Re: Branded types for TypeScript

#149

Post by iainmerrick » Thu, May 16, 2024, 8:46 PM UTC

rough-sea wrote: post #136

iainmerrick wrote: post #133

Earlier quoted context omitted.

No, neither Deno nor Bun does any type-checking. They both just convert the code to JS. To do type-checking you need to run TSC.

deno does type checking. https://docs.deno.com/runtime/manual/tools/check

Oh! I stand corrected. That's a wrapper for TSC, though, right?

Edit to add: I see, Deno embeds TSC as a library and tries to straighten out the mess of tsconfig. That must be a leaky abstraction, which makes me wary, but maybe it works well in practice.

Re: Branded types for TypeScript

#150

Post by davorak » Fri, May 17, 2024, 5:02 AM UTC

DanielHB wrote: post #134

ackfoobar wrote: post #84

Earlier quoted context omitted.

Without your example, I would've bet that TS uses structural typing for interfaces and nominal typing for classes.

I thought so too originally, was very surprised.

This is pretty much to flowjs does

flowtype documentaiton: https://flow.org/en/docs/lang/nominal-structural/#toc-object...

Example: https://flow.org/try/#1N4Igxg9gdgZglgcxALlAIwIZoKYBsD6uEEAzt...