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Comment by amalcon | Hacker News Reader

The author says that this is "why Rust is interesting". I've done a little bit with Rust -- no production code, but some simulations and things like that. While compile time memory safety was the first thing to interest me in Rust, I don't even think it's the primary selling point anymore. The selling point to me is that nearly everything behaves in predictable ways.

E.g. since immutable references are the default, you immediately know whether or not a call will modify its argument. E.g. the existence of traits and compiler warnings for style mean that method naming conventions are incentivized, because implementing a trait usually gives you a lot for free. Even performance characteristics are very predictable, a statement which I can only otherwise make about C and assembly (and those are not predictable at all in other ways).

Yes, the memory safety does play into this. It's much more than that, though: memory safety is just one factor in a kind of pervasive predictability that the language encourages through its very design.

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The biggest selling point for Rust is a non-obvious one and one that is hard to "sell" with screenshots: refactoring. Despite having few tools for automatic refactoring, manual refactoring of large Rust codebases is a breeze: change the portion of code you care about, follow the compiler's complaints and by the end you're likely to have a codebase in a good state. I wouldn't be able to go back to a dynamic language after using Rust for so long, I'd be in constant panic about changing the smallest thing. I equate it to the same discomfort I feel when getting on a car with no seatbelts. I'm just waiting on the day when I can plug the change I want to do to rustfix and let it figure it out, with the help from the compiler.

I think the question was what the biggest selling point is for those who already do e.g. C++, not for those using dynamic languages like Python.

Both questions are important, though. The Rust community is in a very compelling position, in being able to appeal to both the C/C++/'system programming' and the Python/Ruby/etc/'high-level application programming' dev communities.

What I was trying to say was that ease of rafactoring compared to a dynamic language like Python isn't omitted because it's "non-obvious". Rather, it's in fact quite obvious, and simply omitted because it's answering a different question than the one that was asked. Robust refactoring isn't Rust-specific or even new. It's always been the selling point of many statically typed languages, like C++, D, Java, etc.

I mentioned Python because it sits in the other extreme, but the combination of pattern matching, strong types, type inference and ergonomic combinators on the standard library makes the experience much nicer than, for example, Scala. Robust refactoring isn't new. Rust isn't novel. It's just well put together because it had the benefit of hindsight and being able to consider how different advanced features fit together without having to abide by backwards compatibility until recently. Refactoring a single threaded process that operates over a vector can be a single line code change, and the compiler is capable of complaining about data races by leveraging the type system and lifetime analysis.

Much nicer than scala? I don't see how you can claim that if you've touched futures in both languages.

Rust is a nice language for threaded programming, but the async situation is a trainwreck 4 years in the making.

The async situation for Rust is very much in flux, of course - see https://areweasyncyet.rs/ for details and updates. It's definitely a pain point at this time, and stability itself is an important value so I can see this making Rust less desirable for some - but calling it a "trainwreck" that the Rust community is supposedly to blame for just seems pointless, other than as snarky flamebait. That sort of comment is a good fit for `rustjerk`, not for the sort of substantive discussion we seek on HN.

I have touched both and async in Rust is indeed half baked at the moment. That a factor of immaturity of Rust and maturity of Scala. I also had a Scala codebase that had 4 different Future classes, due to it having been an early adopter.

I was thinking if the language itself, where it needs to keep backwards compatibility with Java (the distinction between case classes and classes, for example) and over engineering (implicit action at a distance all over the place). I think Scala is a nice language buried in way too much syntactic sugar. Interestingly enough, Rust's syntax doesn't bother me but quite a few people seem out off by it.

Rust is new and it advances slowly but at a steady state. Given its immaturity in some areas I can only go off potential and the async story seems to have a bright future, despite it's somewhat underwhelming present.

I think you'd be surprised, Rust has seen a lot of adoption & interest from the dynamic languages crowd.

Go and Rust killed my interest in writing Python code. A paradigm shift worth losing amazing libraries and frameworks like SQLalchemy and Django is rare, but I believe we are here (and have been for a while.)

> Go and Rust killed my interest in writing Python code.

Strange to see Go suddenly brought in to support Rust like this. Was it Go that killed said interest or Rust? Why is Go relevant here?

For the same reasons: it offers a strong alternative to C/C++ with memory safety. Often I want performance like C++ but cleaner code and memory safety. Before recently, Python was a go-to when you didn't want to cut yourself on C++s sharp edges, even with it's disadvantages. The overlap isn't clean, but Go is strong for writing simple programs and glue layers, and Rust is strong for writing complex software where correctness and performance are both very important.

Python still has a fair bit of expressive power that Go and Rust would struggle to provide, but I think both can be compelling alternatives in different cases, and they offer a lot in exchange (such as, full type safety and improved performance.)

I realize Rust offers much more safety than Go, but both of them are eons ahead of C++ in this regard. When you're starting from nothing, any level of guarantees is a huge shift.

You're confusing "correctness" with not crashing because of invalid memory access, which is a low bar to clear.

There's really no proof that systems written in Rust have better reliability compared to systems written in Java, Typescript or PHP, is there? I've recently had the same discussion with someone claiming that FP offers stronger correctness guarantees than OO languages: where's the proof?

Furthermore, Rust doesn't offer "much more" safety than Go either, in fact Go's GC suggests that it's harder to make memory handling errors in Go compared to Rust. After all Rust's still vulnerable to memory leaks.

Finally, comparing C++ and Rust reliability is much more nuanced than your dismissive attempt. Modern C++ written by an experienced team + good tooling can have really good memory safety, not as good as Rust, but good enough so that the other advantages of C++ can tip the balance in its favor. The problem: many projects don't use modern C++, or they don't have experienced devs or they neglect the tooling. But here's the kicker - those same teams are unlikely to use Rust anyway.

Here I expect Firefox or Chrome to be given as counter-examples to which I's say that it's likely impossible to write a memory safe browser in C++, due to the project dynamic. Remains to be seen if it's possible to do it in Rust.

>There's really no proof that systems written in Rust have better reliability compared to systems written in Java, Typescript or PHP, is there?

I am not here to prove mathematically that Rust results in more correct programs than PHP. I am here to claim that I believe that it does.

To me one of the biggest obstacles to writing correct code is not just memory safety. It's preventing unintended uses of code. It's handling every case.

PHP is a memory safe language, but that does not mean it is equally good for writing complex software. Why? Because:

- Exception and error handling in PHP, including the standard library, is inconsistent and tricky to get right. In Go and Rust idiomatic error handling is pretty easy to get actually correct.

- Code is not only not type safe, but you might not even notice when you violate type safety. Many things that are runtime errors in Python and compile time errors in Rust or Go are incorrect behavior in PHP.

- The TypeScript, Rust, and Go compilers and toolchains are more rigid, because more strict languages make that possible. For example, if you fail to return in every possible code path of a function, that's an error. In TypeScript, any unchecked possibly null access is an error when using strict nulls. Many more examples exist.

>Finally, comparing C++ and Rust reliability is much more nuanced than your dismissive attempt. Modern C++ written by an experienced team + good tooling can have really good memory safety, not as good as Rust, but good enough so that the other advantages of C++ can tip the balance in its favor.

OK, it feels like you're just being contrarian now. I've made this same argument before as a reason why we shouldn't all just rewrite everything in Rust.

I've worked on a fair bit of large C++ projects before. My current employer, Google, does quite a great job with the C++ toolchain, and admittedly while I do not have as much experience with it as I do C++ outside of Google, I'd say it's close to the best I've ever seen.

And even then... It's ass ugly, the errors are confusing as hell, I can't understand what the hell is going on in some of the macros, and it's still possible, with metric tons of safeguards, to fuck up and segfault (guilty.)

Something C++ fans (including me) love to point out is that if you enforce the use of smart pointers you effectively can prevent whole classes of memory issues. In reality I'm pretty sure everyone knows that's a bit of an exaggeration. It's still pretty easy to misuse a smart pointer. And on top of that, smart pointer syntax can be confusing. I used to be a huge proponent of operator overloading but after not having it for a while I'm pretty sure it has a tendency to turn verbose code into confusing but terse code.

C++ just has too much fucking syntax. And it has templates. And on top of that syntax it has text macros. And even if you ban new macros, you still need macros for very basic things like "logging with line numbers". And it's useful for things where none of the other available tools solve the problem. So good C++ code probably ends up using a lot of macros even if most of it is not defining new ones.

People have made C++ fault tolerant as much as possible because they have to. There's too much C++ in the world to stop and rewrite it all in some memory safe language. No amount of language debates on Hacker News will ever change that.

But, we should not let that cloud the fact that better C++ doesn't come close to providing strong safety guarantees, and it sure doesn't prevent obscene looking code. As much as people will hate Gofmt, I've never seen uglier code than some of the edge cases as handled by clang-format. (If you know of a C++ formatting tool that's any better, please tell me.)

So does Rust result in more correct code? Does Go? I believe so yes. For starters, C++ error handling is atrocious. Some people use exceptions, some people don't. Google uses StatusOr[1] and I think the best case would be something like Andrei Alexandrescu's expected<t>. In reality you get a mix of custom status codes, C style error handling, weird OOP style error handling where objects contain error statuses (especially when you can't throw in a constructor.) Even at Google there are third party libraries, with both C and C++ APIs, so there's still some mismatch that has to be dealt with. The standard library is just as guilty here.

How about safety? Even with improvements it's really hard to make a subset of C++ where you can't accidentally segfault. Sometimes, you have a smart pointer and you need a regular pointer. So what do you do, dereference? Well sure... But now what are you thinking about? Lifetimes. And thus, the value proposition of Rust. Go solves the lifetime problem with garbage collection, but in C++ you just have to manually, as a human, figure out what lifetimes are expected, and in the meantime someone could submit code that subtly changes this and when you submit your code now head is broken even though neither person made a mistake.

The list really could go on for a long time. And I expect every point here to be disputed because there's some way to mitigate the problem. Reflect for a moment, though, that all the energy spent trying to mitigate problems like these could've been spent on writing better code elsewhere if it weren't for the shortcomings of the language.

1: http://www.furidamu.org/blog/2017/01/28/error-handling-with-...

I very specifically said reliable systems, not functions, libraries and so on. So you're claiming that Rust systems are more reliable than PHP ones, another person's claiming that Haskell's more reliable than C++ and yet another that Go is more reliable than Python.

Once again, where's your proof? You know, studies, experiments, demonstrations comparing real-world (or even dummy) projects and concluding the above? Because gut feelings aren't going to convince me, or any other questioning individual.

Almost all these claims, including yours (not surprising at all) revolve around the idea of encoding relationships and allowed operations in the type system. I'm calling this "reliability in the small", or the ability of writing statements and functions which are restricted from performing specific non-desired operations. These do have a positive effect in my opinion, but not enough to result in more reliable systems overall. A pretty well known tenet of safety engineering is that putting together reliable components does not mean one gets a reliable system.

Frankly, I think it's other things that really make a difference: thorough code review, formal specifications, design by contract, automated testing, taking time to gather requirements and design things.

I'm not going to spend time addressing your points regarding C++, because let's be honest, you wrote way too much :-/ In principle you're correct to say that it's easier to write memory-safe Go or Rust code. C++ requires more effort to get there and C++ teams tend to prefer performance to safety.

It is not easier to write correct Go or Rust code compared to C++. Memory access violations aside, there are many more bug classes which aren't prevented by any of those languages. Rust is constantly being oversold, there's nothing that makes it any better than say Java or Swift, on the contrary, the former are much easier to pick up.

>Once again, where's your proof? You know, studies, experiments, demonstrations comparing real-world (or even dummy) projects and concluding the above?

I explicitly said no. I'm not here to fulfill your personal requests. If that's what you want, Hacker News comments are probably the wrong place to ask, and I'm not personally interested in conducting such studies. I'm already convinced, so it wouldn't really benefit me much.

>Because gut feelings aren't going to convince me, or any other questioning individual.

OK. This isn't gut feelings though. It's a discussion about subjective matters.

If that was too much writing, then so is any meaningful discussion about the differences between programming languages. I'm not going to attempt to discuss this further.

The whole point of my initial reply was to challenge an oft repeated belief that using FP results in more reliable systems. This belief doesn't really have solid proof behind it.

If you're not providing that proof because it's beneath you, or for some other reasons you've really just wasted everyone's time here by repeating the same appeal to feelings and personal experience for the Nth time.

I addressed the core of your arguments against C++. The rest has been discussed before by myself and others. It's nothing new on HN.

> But here's the kicker - those same teams are unlikely to use Rust anyway.

Absolutely disagree. Those are exactly the teams that will choose Rust over C++. It is well known that many shy away from writing plugins for node or python in C/C++ specifically due to the fact that they don't have enough experience with these unforgiving languages. The gap between Python/JS and C/C++ is wide and deep. But the use case is still there. If you have to improve performance of a component - Rust provides a lower barrier to entry and will be chosen by such teams.

Erm, the teams that are using C++ and having reliability issues due to lack of memory safety are the ones that will choose Rust?

In my experience they just fix their bugs and move on with their lives. Probably you were thinking of some other teams, since you're mentioning plugins for Python.

Go has garbage collection support, so it's definitely more convenient in some specialized domains than Rust - namely, those which inherently involve spaghetti-like allocation and "ownership" patterns that RC alone can't deal with very well. You wouldn't want to rewrite a typical LISP codebase in Rust, but with Go you could make it work and get good performance out of it.

(You could of course use a ECS-like pattern in Rust and end up with a half-baked reimplementation of a Go or LISP runtime, but the ergonomics would not be there.)

Another point is that using rust is great for products, but not so much for PoCs, since the compiler will complain about most ‘hacks’ to release early, or even refuse to compile.

I have not much experience with go, but my feeling is that it should be faster to have something working, and then if it’s worth it (e.g. if it needs high performance with concurrency), migrate to rust.

Yes and no. Yes, Rust requires more "mental cycles" to think upfront about the design, even of a simple tool. But, as they say, nothing is more permanent than temporary. A tool that you write as a one off, before long, ends up running critical infrastructure in production.

We all have been in the situation where we quickly put something together. With Rust -- you internalize some of the things you know the compiler will demand -- so tenth time you write something in Rust will be faster. But the beauty is that Rust compiler will force you to _gradually_ fix the design of your tool and the extra time you spend fixing it pays dividends when this code eventually becomes something everyone relies on.

Coding in Rust is like an investment: it requires some commitment and slows you down initially (for the right reasons!), but pays huge dividends and return grows exponentially over time.

> Coding in Rust is like an investment: it requires some commitment and slows you down initially (for the right reasons!), but pays huge dividends and return grows exponentially over time.

Kind of my point. Sometimes you don’t want to make an investment, sometimes you just need something to show.

You can cut corners plenty easy. .unwrap(), .expect() and so forth. The great thing about that is, all the places where you cut corners are blatantly obvious and searchable.

> I wouldn't be able to go back to a dynamic language after using Rust for so long, I'd be in constant panic about changing the smallest thing.

As someone who has been working mainly in Rust for about a year and is now starting to pick up Python, this is huge! I pretty much never write Python that isn't explicitly typed thanks to how Rust changed me as a programmer.

Same. I think Rust has been the biggest thing for me in terms of growth as an engineer in recent memory, and I've worked across the stack from HDLs to embedded to mobile to desktop to server over the course of my career.

I'm really glad to see that there is a huge resurgence in support for statically typed languages in mainstream programming. I always felt that this was somewhat inevitable, but the tide of opinion was against it for a while. I completely agree, and the inverse situation is true too. If you're used to statically typed languages, working with a dynamically typed language can be hellish if your codebase is suitably complex! And by suitably complex I mean more than >500LOC. ( That's not a typo, the omission of the 'K' is intentional. )

I'd love your thoughts on this, my guess is it's because of ergonomics improvements. Specifically, inferred types. This middle-ground lets you have much of the ergonomics of a dynamic language but with the safety of a static one. You may have to hint it from time to time, but for the most part (99%+) Rust guesses the types of everything I do day to day, and when it doesn't know, it ... asks.

In some sense. I mean, type inference is not new. But the languages that really brought static typing to the masses didn’t use it, or only did deduction, so it is “new” to a lot of programmers.

I do think that there’s a relationship between power and usefulness, but more power isn’t always better. I’d rather use Ruby than Java 1.5, but I’d rather use Rust than Ruby. YMMV.

It's kind of sad to me that (almost) complete type inference has been around since the [70s](https://en.wikipedia.org/wiki/Hindley–Milner_type_system) and it's still not mainstream. (unless you consider F# or OCaml mainstream languages)

Type annotations at the signature level are documentation, so I'm not so sure if global type inference is really better than local type inference. Also HM type inference doesn't play nice with type systems with subtyping or method overloading.

OCaml does have subtyping (albeit with a clear separation between that and implementation inheritance) and method overloading, but its type inference accommodates those. Or am I missing something?

Seriously asking: How does it work for undecidable cases? Nominal subtyping may cause ambiguity where both supertype and subtype match. Overloading may cause ambiguity where more than one overload matches, and depending on the overload we can infer different types.

BTW I didn't say it was impossible, only that it doesn't play nice and probably is no longer a pure HM system. The search space is definitely much bigger with overloading and subtyping.

It still has classes, and implementation inheritance with method overloading, but they're completely decoupled from subtyping (so e.g. subclasses are not necessarily subtypes - a class can use self-type in an argument position). And types themselves are structural, with row variables and polymorphism. If you need to define an equivalent of a named interface, you just define a type alias, like any other. And when you define a class, you get an auto-generated type alias for the structural type of objects that it will instantiate. [1]

End result actually looks surprisingly familiar to someone coming from C++ or Java, at the first glance. It's really a shame that it's not something that OCaml is famous for; it deserves to be. I wish I could have an object model that expressive in C#.

[1] https://caml.inria.fr/pub/docs/manual-ocaml/objectexamples.h...

Inferred typing is just a feature of statically typed languages. Static typing just refers to the type of a variable being known at compile-time. Type inference is the ability of the compiler to infer the variable's type from the context of its declaration. It doesn't mean that there's any loss of safety at all, it's just a matter of syntax.

Yep, exactly; I was suggesting that the move in modern languages towards inferred typing is what makes statically typed languages pleasant to work in, which has lead to their return to popularity. Sorry if I wasn't clear!

Oh, pardon me. I re-read your post and it makes more sense to me now! Maybe that plays a role. I more attribute this, somewhat in jest, to enough time having elapsed since the renaissance of dynamically typed languages began for developers to have gotten sick of maintaining codebases built in them. I also, very cynically, think that there's a very contrarian and competitive streak running through the development community which drives developers to always seek to move against the majority. Cultivating a kind of heroic self-assertion in the process. Think, for example, of the resurgence of interest in functional programming and the aggressive proselytisation on its behalf. In defence of my polemic assertion here, I have somewhat cultivated this idea around myself and my own shortcomings. Also, even when I program in languages featuring type inference I usually mandate that my team use explicit type declarations for the sake of clear declaration of intent and better tooling support, that's just one opinion there though.

“change the portion of code you care about, follow the compiler's complaints and by the end you're likely to have a codebase in a good state.”

That has always been my refactoring algorithm with C++, C# of TypeScript now. I know a lot of smart people using dynamic languages but I always prefer to lean on the compiler to tell me what needs to be changed.

This is one of the big reasons I use TypeScript over plain JS as well, especially when combined with TSX for typesafe views.

> refactoring of large Rust codebases is a breeze: change the portion of code you care about, follow the compiler's complaints

At my $DAYJOB I write a lot of Java, and modern full-featured IDE's for Java like IntelliJ are absolutely awersome for refactoring. Most common refactorings are fully automated, and many more complex things are very easy to do by combinding some of the base refactorings.

I really like writing Rust in side projects, but after getting used to the phenomenal support refactoring support in Java, having to follow the compilers diagnostics feels very primitive.

Jetbrains' refactoring tools have always been top tier. For years resharper was absolutely essential for C# development because visual studio just lacked good refactoring. VS has been catching up and has mostly caught up in recent editions but I doubt that would have happened if not for MS being able to see just how popular resharper is.

I'd hope that as Rust grows in popularity the tooling will come from that so I'd keep an eye on the intelliJ rust plugin or rider support for rust because as you say, it's really difficult to go from a day job where for example promoting a local variable to a parameter (with replacement at the call sites) just works to one where you actually have to think about manual refactoring.

> I'd hope that as Rust grows in popularity the tooling will come from that ...

Patches are welcome! https://areweideyet.com/

The Rust plug-in, is already quite nice, and getting better all the time. I use it from CLion, since that has integrated debuging support.

One reason why I'm optimistic about Rust is because the team not only explicitly recognizes the need for advanced tooling (such as IDEs), but owns critical parts of the underlying infrastructure, such as RLS. If you want a language to have quality tooling, it needs to be designed for that, and there's no better forcing function for that than having to write that tooling yourself, or at least having someone who does on the same team, in constant communication.

IntelliJ plugin for Rust can do some refactoring (renaming functions and variables - it's all I use and remember).

For Rust development I use CLion with the Rust plugin, and it is getting better and better all the time.

It is interesting seeing the difference in peoples expectations on what an IDE can and should be able to do for you depending on what they are used to working with.

You are mixing "fancy tools for mature language" with core capabilities of another (that will enable even better fancy refactoring tools in future - tools that can make more complex refactoring tasks fully automated). If anything, the fact that what used to be an external tool has migrated to core feature in Rust is a testament to how forward looking the language is. Imagine what that will enable in tools to come!

I fully expect rustfix to gain refactoring capabilities, even if haphazardly bolted on. Things like changing an owned field to become a borrow requires a lot of trivial changes that can be automated away (other than making sure the field been borrowed has an appropriate lifetime, it course) that for the most part rustc already emits as structured suggestions that other tools can use.

I'm not implying that Rust should have these yet; I am fully aware that the situation for Java is different due to serious and long efforts in developing great refactoring tools.

The point I was trying to make is that the view that Rust is great for refactoring depends heavily on what one is used to. For example, as compared to any dynamically typed language, a strongly typed language will be better for refactoring.

Writing refactorings that work reliably is very complex, and I'm not sure if it is practically possible to write the same kinds of refactorings that Java has for Rust. Two of my favourite refactorings in IntelliJ are extract method (with automatic duplication finding) and inline method/expression. I think that such refactorings are a lot more complex to do reliably in Rust due to ownership and borrowing rules, unnameable types, and so on.

Actually I got into rust because it is the only language that has both ADT/patten matching and a practical mindset/community. There is simply no alternative. I would even code front-end rust for the sake of this.

Reasonml also has adt and pattern matching

True, and swift. They are nice to work with too.

E.g. since immutable references are the default, you immediately know whether or not a call will modify its argument.

You do not, since the type of which an object is referenced could use interior mutability (e.g. RefCell). So, you only know if this is the case after inspecting the type.

Of course, the default in Rust is to use exterior mutability and in general, interior mutability is/should be avoided.

(I agree with the general thrust of your comment though.)

Rust's mutable/immutable is better thought of as exclusive/shared. But in any case, the interior mutability is not causing problems, because the compiler still largely enforces it's used correctly (e.g. no matter how deeply RefCell is hidden, code using it won't be able to share it with another thread, so you don't need to worry about getting a data race this way).

I fully agree with you, and actually I want to write a summary of those less-discussed features that have high productivity impact including the predictability you mentioned in the future.

Though, for the people who haven't explored Rust yet, I still think that focusing on the memory safety, the most powerful feature, is a good approach. Personally I tried explaining other smaller benefits first, e.g., immutable by default, move by default, no header files, but didn't work well as I thought. Exploring another language is a significant investment, and people need a significant reason (at least those that appear to be at first glance).

And there is a small marketing problem for Rust. The memory management is the big ticket thing we like to show off, but the big benefits of the language are much smaller and boil down to quality of life and composability.

Yes, banging on about memory safety sells Rust short, and drives away exactly the people who would benefit most from improved memory safety.

The language is just overwhelmingly better to code in than C, or Java, or C#, or Go. If the compiler were to be made fast -- and there is nothing like a fast compiler coded in your language to advertise its speed (and the reverse!) -- or anyway JITted, with a REPL, it could replace a great deal of scripting.

The comparison to C++ is much less compelling. Rust fans like to lump C and C++ together, but in modern C++ there are few temptations to memory unsafety. (They might be misled by crufty Mozilla code.) Meanwhile, the greater expressivity of C++ enables more powerful libraries, and each use of a good library eliminates many more than just memory bugs.

I agree with you, for sure. We had a huge community discussion about this in 2016: https://brson.github.io/fireflowers/

Rust has a great type system that enables the kinds of things you're talking about. It's like c++ and haskell came together and had a baby.

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