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Comment by ikety | Hacker News Reader

I'm interested in what scenarios you don't get this same feeling when writing TS code? I of course agree with Ruby, JS, and Python.

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One big source of bugs in TS is structural sharing. Like, imagine you have some complex object that needs to be accessed from multiple places. The obvious, high performance way to share that object is to just pass around references wherever you need them. But this is dangerous. It’s easy to later forget that the object is shared, and mutate it in one place without considering the implications for other parts of your code.

I’ve made this mistake in TS more times than I’d like to admit. It gives rise to some bugs that are very tricky to track down. The obvious ways to avoid this bug are by making everything deeply immutable. Or by cloning instead of sharing. Both of these options aren’t well supported by the language. And they can both be very expensive from a performance pov. I don’t want to pay that cost when it’s not necessary.

Typescript is pretty good. But it’s very normal for a TS program to type check but still contain bugs. In my experience, far fewer bugs slip past the rust compiler.

Appreciate it, that makes a lot of sense. I feel like I've been trained to favor immutability so much in every language that I sometimes forget about these things.

Similar. I mostly design my code around something like pipe and lifetime. The longer something needs to live the closer it is to the start of the program. If I need to mutate it, I take care that the actual mutation happens in one place, so I can differentiate between read and write access. For anything else, I clone and I update. It may not be efficient and you need to track memory usage, but logic is way far simple.

Yes, immutability is great for safety. But the copies you have to make to keep everything immutable extracts a price in copies and garbage collection.

Rust is advertised as having fearless concurrency. That's true, but not that important as concurrency is not that common. What's important to everyday programming is Rust provides fearless mutability. The fearless concurrency you get with that is just a bonus.

Fearless mutability provides Rust the same safety as a functional language in a without the speed or space cost. IMO, it's Rust's true secret sauce.

Yea this seems like a super power I thought only functional languages had. I have to make time to learn some Rust

Not parent comment, but TS is generally safe if you have types correct at system borders, but very scary when you don't. Some of the most impactful bugs I've seen are because a type for an HTTP call did not match the structure of real data.

Also, many built in functions do not have sufficient typesafey like Object.entries() for instance

The worst offender is toString which has different types between objects and is everywhere by default.

That is an issue with how TS works, but it can be significantly improved upon by using a library to verify the structure of deserialized data. zod is one example, or you could use protobufs. Fundamentally, this is an issue with any programming language. But having your base "struct"-like type be a hashmap leads to more mistakes as it will accept any keys and any values.

I disagree that this is an issue in every language - the problem is that in other languages the validation against some schema is more or less required for unmarshalling, and it's optional in TS.

Seeing a deserialization error immediately clues you in that your borders are not safe. Contrast that with TypeScript, where this kind of issue can lead to an insidious downstream runtime issue that might seem completely unrelated. This second scenario is very rare in other languages.

I don't know Rust, and I'm genuinely curious: How does it improve over that problem?

When you call a REST API (or SQL query for that matter), how does it ensure that the data coming back matches the types?

TS allows you to do parse the JSON, cast it into your target type, done (hiding correctness bugs, unless using runtime verification of the object shape, see sibling comment). Does Rust enforce this?

It validates the object shape at runtime, much like you can do in Typescript with a library like Zod. The key difference in this case is that Rust makes it scary to not validate data while Typescript will gladly let you YOLO it and blow your legs off, even in strict mode.

Okay I see, that's a nice secure-by-default point, whereas TS is arguably not secure-by-default.

It’s not. And trying to just be a transformation of the source to JS without its own standard library (mostly, some old stuff doesn’t follow this) means it really isn’t possible with just TS alone.

That’s OK with me. I use TS because I like it and hate the total lack of safety in JS. I have to use JS on the web, so TS it is.

If I don’t need it to run on a webpage, I wouldn’t be writing it in TS. I like other languages more overall.

What do you mean by "safe" in this context?

If you type correctly at border of your system, then TS will be very close to a formal verification of your code. This won't catch all bugs, but even broad categories for you data is helpful. If you know your input is a non-null string. Then it will warn you of every non string usage. It won't catch whether it's a name or an email, but knowing someone tries to divide it by zero is helpful.

It's a lot more effort, but branded types for conceptual differences can bridge that last gap

Typescript doesn't even support notions like "unsigned integer". It is not a serious attempt at type-safety; its main claim to fame is "better than raw Javascript" which is not saying much.

If you need to run in a JS environment it’s a hell of a lot. It’s a FANTASTIC improvement.

I wouldn’t use it server side or for a client application that doesn’t run in a web browser. That’s not its place, for me.

But I will 100% reach for it every time if I need to run in a JavaScript environment.

TS actually works very well as an HTTP server, I’d say better than typed Python. Plain JS… a minute of silence, please.

I’ve never been a JS on the server person, I was used to other languages when that was developed.

Well I think I would prefer python, but simply because it’s “more traditional“ and I realize that’s specious reasoning, I prefer to use strongly typed languages whenever possible.

I would generally reach for Java since it’s the language I’m most proficient in due to my career. There’s also Go, which I played with long ago, or maybe I’d try Rust.

This is only for anything important. If I was just toying with something locally I’d probably do whatever was fastest. In that case Python or JS might be my choice for a very tiny script.

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