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Comment by Manishearth | Hacker News Reader

I don't really understand the "Rust is obsessed with memory safety" meme.

When pitching Rust to others of course memory safety and thread safety get hyped a lot; because it's talking about something that most languages just can't do -- safety without compromise.

But actually ... memory safety is a small part of the reasons why I like Rust, and there are plenty of other cool bits in the language. It stands out a bit because it's different, but that doesn't make it the end-all goal.

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Safety without compromise doesn't exist. Rust does what it does well, but at significant cost in developer time. I'd rather use a garbage collector, it's much much simpler and fine for 99.9% of use cases.

Garbage collection does make things easier, prettier, and simpler. BUT there are many problem domains in which a GC can not be used. A browser being a prime example...

Maybe you can find a better "prime example" than browsers, which nowadays are mostly known as execution engines for JavaScript, a garbage-collected language.

But frankly, I doubt that you can. Others will say "operating system kernels", but people are happily writing OS kernels in OCaml, so <shrug>.

Yet others will say "safety-critical hard real-time tiny microcontrollers without an MMU" (one of Ada's domains), but on those systems you don't want to do dynamic allocation anyway, so the question of GC or not is kind of moot.

I've said it before, I'll say it again: Rust would be a better language if it had a GC and the possibility of marking certain program parts as GC-free (the way it allows you to mark certain parts as unsafe).

That's kind of his point, you can't write a GC language interpreter in a GC language forever, eventually you need a non-GC language to actually implement the GC in. So in this way writing a Javascript executor in a GC language wouldn't really make sense, you're just adding needless layers of abstraction (at a serious performance cost). So I think a browser is an excellent example of an application which can't really be written in a GC language. Other examples might be Databases and realtime applications.

> you can't write a GC language interpreter in a GC language forever, eventually you need a non-GC language to actually implement the GC in

Here's PyPy's GC, implemented in Python: https://github.com/tycho/pypy/tree/master/rpython/memory/gc

(I haven't looked at it in detail.)

Anyway, even if you absolutely had to use a non-GC language to implement a GC, that would not preclude writing 99% of the browser in a GC language and only the GC in something else.

How do they compile/interpret PyPy's GC, is the compiler/interpreter written in a GC language? I said you can't do it forever, eventually you need to drop to a non-GC language (I feel very certain of this, so if I'm wrong I'd really like to know).

Also, why would implement GCs multiple times at different levels of abstraction in the stack, other than for something specific like PyPy which is specific like designing an interpreter to help test language features quickly?

Of course you need to drop to some sort of non GC language, or you would need a hardware GC. However look at Iota [0], that can compile LLVM to Common Lisp. So you can run GC and non GC languages within, kind of, Common Lisp. Or look at all the projects that compile a language to javascript, and there is no reason why the reverse could not be done.

[0] https://github.com/froggey/Iota

PyPy is originally bootstrapped on the C Python interpreter, but it can then interpret and compile itself without relying on CPythob anymore. If you insist, then once PyPy is bootstrapped, the "drop to a non-GC language" is its process of having compiled the garbage collector's Python code to machine code.

But you're still wrong on this drop being necessary, I think. You can do it just fine in a language with GC that also allows you to allocate a block of memory that is not considered by the GC.

> But you're still wrong on this drop being necessary, I think. You can do it just fine in a language with GC that also allows you to allocate a block of memory that is not considered by the GC.

I think it's a bit disingenuous to say a "GC language compiled a GC language" when the compiler used non-GC portions of the language to do it. You're right, I should have said "A language which can work without a GC" instead of "a non-GC language;" but I think the spirit of my comment was clear.

That said I think what you said above is right, and non-GC code is really only necessary in the hot parts of an application (and applications that can't use dynamic allocation for whatever reason, but that's another discussion). Rust is even working on adding GC support [1] (albeit very slowly, as they should). That said non-GC languages (or at least the ability to write code that doesn't use a GC) is still necessary in many industries for many reasons; that isn't going to change for a long time, if ever.

[1]: https://manishearth.github.io/blog/2016/08/18/gc-support-in-...

"safety without runtime compromise", fine?

When things such as the borrow checker are so heavily built in to the language, I find it hard to to see how Rust isn't ultimately intended to do memory safety. Obviously it does other things, and I'm sure it has some cool ideas in there. But I have a hard time seeing how it's a mischaracterization of Rust to say that memory safety is kind of it's thing.

I don't understand why the public marketing effort is so focused on safety, either, but it is. When I see Rust mentioned, e.g. here at HN, I cringe a little because odds are it's in the context of how unsafe everything else is, or there is at least some connection made to safety. "Obsession" seems loaded.

Rust is a very nice language with many useful and interesting features which may exist because of the developers' focus on safety but can very much be marketed without calling out safety all the time, and especially without the hints, suggestion, and innuendo that using a language without Rust's safety model is somehow dirty, dangerous, or worse irresponsible or unethical.

By "public marketing effort" do you mean "people talking about Rust"?

Personally, I interpret the focus on memory safety as a response to "memory issues aren't a big deal" or "memory issues only come from incompetence" viewpoints.

Again here the word "safety" starts to get rather muddy. What Rust calls safe is not what Ada calls safe. I'd rather be specific about what we're talking about.

Memory safety is not, itself, program correctness. It's just one way programs can go wrong.

https://brson.github.io/fireflowers/ for example

>... and there are plenty of other cool bits in the language.

Could you elaborate what you think is cool there ("other cool bits")? Serious question, I'd like to hear a personal opinion.

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