Rust is quietly spreading as a language of choice to build reliable and perform in applications, but what makes it different? Alice Real is a software engineer working on Google's Android Rust team, a core maintainer of Tokyo, the de facto async runtime for Rust, and is a Rust-language team advisor. In today's conversation, we cover the pitch on why Rust is worth to consider whether you're using TypeScript or C++ today, how concepts like ownership, the borrow checker, and the unsafe keyboard work, and what are things that trip up newcomers to Rust, how the language is governed without a benevolent dictator, and how RFCs and additions work, and many more. If you want to understand what makes Rust different, and why so many engineers say, once it compiles, it works, this episode is for you. This episode is presented by Antisys.
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Alice, welcome to the podcast. Thank you for having me. It's really nice to have you here. How did you get into software engineering? It actually all started with Minecraft. No way. I wanted to write my own mod for Minecraft,
though I don't draw it. I didn't get very far with the Minecraft modding, but that's where it started. How did you continue? Did you go to university? This was just before I started in high school, and then after high school, I had a year where I worked full-time as a software engineer, and then I moved on to the bachelor. Did that for three years,
and then I did a master's for three years. How did you end up at Google? Was that straight out of university? I actually started part-time at the same time as when I started my master's, and then I switched to full-time after I finished. How did you get involved with the Rust community?
Was it at Google? Was it before Google? Way before. I've been doing Rust for a long time. When I was in school, I spent a lot of time on the, what's called the Rust users forum.
Well, I was answering questions, really. I have maybe 10,000 posts on there or something. At some point, I also started being active in some chat server, the discord server for something called Tokyo. I kept doing that, answering questions. When I saw common questions, I would fix the documentation. That's how I got into Tokyo, which I'm now one of the maintainers of.
And then for those of us not as familiar with Rust and Tokyo, what is Tokyo inside of us? And why is it important? So Tokyo is, well, it's an asynchronous runtime for Rust. You can think of it as the standard library for Rust when you're using async. I mean, if you compare with something like JavaScript in the browser, you might compare Tokyo with the browser itself. For example, in JavaScript,
you have this loop, this event loop, which has all the tasks that are able to run and then they get executed one after the other. And especially if you use the await stuff, then you can have tasks, pause, and then another task not running on the same thread. And Tokyo does something similar. It has a queue of things that are able to run, and then it will run them. So unlike JavaScript, Tokyo can be multi-threaded. So you can have multiple queues running in parallel.
This seems like a pretty core part of Rust as a language, as an ecosystem. How did you gravitate towards this? Because it sounded like you were, if I understand, you were lurking on the Rust forums, you were helping out here and there, what drew you to this part of the language or the ecosystem, should I say? I think part of what I liked about Rust is this feeling that as you write the code, when it compiles, it works. I mean, this has to be in quotes, because obviously it's possible that there are bugs. But this is something a lot of people say about Rust, and there's a reason
people say it, even though it's not necessarily literally true. How do some other languages compare? To begin with, I think, to have a language that feels this way, you have to have a type system. That's where it all starts. I do think that even compared to other languages with type systems, I think Rust does a better job than many languages, even others with type systems.
The classic example is Java's null. It was Tony here who invented the null, and he called it his billion dollar mistake, because it's so easy to have, I mean, every time you call a function, you might have a crash in your program. And in Rust, I think they're really good at making sure that when you call a function, there's no chance that it might be null. That problem just doesn't exist. You can't have that kind of crash. And so you have to explicitly say, this object might be null,
and then the compiler will force you to check for null before you use it, so you can't forget. Can we talk about Rust as a whole? This was a language that was created in 20 years ago, in 2006. And it feels like it's become a lot more popular over time. Do you know of the scale that Rust is at in terms of usage or popularity or things along the Rust communities, the numbers that are known there? One thing I found kind of funny, I checked here all the day, and we have actually overtaken
PHP and Go on the Taiobi index. That index tries to estimate the usage of languages, right? Usage or popularity or something like that? Wow. Because the feeling I have again in general is that Rust is popping up in more and more places, more companies are building on Rust.
Oxide is a good example. They decided to go all in on Rust. And there's a sense of Rust is becoming a popular place to build high-performance applications, even increasingly contributing to the kernel as an engineer who might know other languages from TypeScript, Java, etc. What would your pitch be on why it's worth checking out Rust or working with Rust? That depends a lot on which language you're coming from. Let's come from TypeScript. It's one of the most popular languages
right now. The pitch from TypeScript would be a lot different than the pitch from C++. But, okay. So to begin with, I think when it comes to TypeScript, Rust fits in as the backend language. That's where I would put it. I wouldn't use it in the front end. I think it's a pretty good
fit for backend API servers. One way to put it is you don't want to be waken overnight because there are problems with your web server. You need a language that's reliable, that's going to have as few bucks as possible. I mean, obviously it would be nice if that's zero bucks, but it's going to be hard to get there. But as few bucks as possible, that's the idea of Rust. I mean, I already mentioned
null, but it does a lot of stuff like that. So there's no null checking and this is done through, it has this enum type, which I think TypeScript can do something similar, TypeScript is actually kind of good on that front. But, okay. The other thing I think is quite good is error hunting. So, on one hand, Rust doesn't really use exceptions. So it actually returns the error as a value. So,
you return a value that's either using an enum, either the result or the error. And the way this is done is that there's an operator, question mark, which says, so you write my function and then question mark at the end. And this means if this function fails, return the error. So, it's really easy to handle errors, but it's not zero characters like this with exceptions. So, it's explicit. On the other hand, and if you forget to put the question like that's a compilation error,
so you have to check it. And of course, you can also handle it. But the point is, it's this idea of, there are these things where you write some code and there's some implicit error condition you didn't think of. And now you just took down your circle or something. Another thing I quite like is how it handles documentation. For one, when you have a comment, you make it into a documentation
comment by having three slashes instead of two. Now, the thing is, you can, of course, write examples in your documentation. And Rust makes all examples into tests. This means that if you change the underlying code, now your test fails. And so, this means that you can't even, you can't forget to update your examples in your documentation. Yeah. And I guess there's also things
like you can you forget to initialize a variable in Rust? I mean, no, it doesn't allow you, right? Yeah, you have to set a value before you use it for the first time. Yeah. And I guess the things with checking the format of incoming JSON, it also forces you to do that. Yeah. So, that's a pretty
cool library called Sir Day in Rust, where you, you have your struct, so your type, you know, with fields. And then you can say, I want to be able to pass this from, for example, JSON. And then, Sir Day will, it's a macro, it will generate code, which checks the JSON that it's in the same format. It has all the fields you need. And they have the right types and it generates native code that's specific to that particular shape of JSON. So it's also really efficient. And again,
yeah. And so it helps you avoid errors. And there's this thing which, again, I learned just very recently, thanks to, thanks to you guys, we're talking ahead of this, is the switch statement, right? So in almost every language, you have a, you have a switch for an enum and you handle cases and then you might have a default or, you know, everything else. And sometimes you forget one of them is not a big deal or maybe it's a big deal. But in Rust, you cannot do that here, right?
That's right. So in Rust, it's not called switch, it's called match, but it's the same idea. You can match on your enum and then you can have a branch for each possibility of my B. And if you are missing one, that's a compiler. Of course, you can have a catch all case if you want to, but most of the time you would just list all the cases. And then in the future, when you're at a new variant, the compiler
will tell you, Oh, you need to update your code here, here, here and here. And I think this is kind of lead to another way that Rust really helps with reliability, which is that if you're refactoring, I think Rust is really good at telling you all the places you need to update. I've done this sometimes where I would refactoring something, I changed the code, I changed the return time, whatever it is. And then I just fix the compiler errors until the compiler stops shouting. And then once I've done that, I've updated every place I need to update. I get a sense that the language designers have
thought really hard of what are ways that typically go wrong in a lot of the programming languages. And they just try to fix it through a compiler. The documentation example is the one where I'm still like, wow, like it happens all the time. Like you have a comment, example or not, and then it gets out of sync and we always complain about this and we don't know how to fix it. I know I've been complaining for like a decade plus. This draws to the first language right here, like an actual
solution, even if it's not a perfect one. And I really think this pattern just everywhere you look, you have this kind of thing again and again that, Oh, if you messed up, they, you know, either it won't compile, but the very least there's a link for it. They just catch a lot of cases at compile time. And we've had this pitch from TypeScript or similar languages. What about the pitch from C++?
So here, actually think it's even stronger. The thing with C++ is that if you make a mistake, right, in JavaScript, maybe you take down your server, which is already bad enough, but it's plus when you make a mistake there, now it's actually a security vulnerability most of the time. If you do something as trivial as you did on off by one in your IRA or whatever it might be, that's a security vulnerability. And that just keeps happening. Small mistakes become security vulnerabilities. And in Rust,
so Rust is memory safe, right? I mean, we talk a bunch about different ways that Rust is more reliable, and we didn't even touch about memory. Let's talk about memory safety. Memory safety is this idea that no matter how stupid the code you write is, it's not going to have a certain class of bugs. And this is the kind of bug that usually leads into security vulnerabilities, you know, the kind of thing where you re-pass the array and you just look at random memory, or you destroy an object, and then you use it afterwards. So now you actually charge the memory of some
other random object. Yep. And then a attacker who figures this out could populate something there, eventually get that code somehow executed or configuration read and then boom. The classic example in the kernel is let's say you have some object and you managed to make it so that the object that's actually there, right? Because the original object is gone. So the memory got reused, and now it has
a task struct, it's called, and that's basically your process. And it has a field called user ID, and it's pretty common for code to write zero to memory. But if you write a zero to the user ID, that's your root. That's a root user. Yeah. That's a really classic way of exploiting this kind of
vulnerability. And then once an attacker manages to do that, they can take over the whatever your server is running. And then of course, from there on, it can just fire a lot of control, right? Once you have root, you can do it. Yeah. Do I understand that a very strong pitch of rust,
especially coming from C++ is memory safety eliminates this whole class of bugs, which can train security vulnerabilities, which are one of the most serious threats any software can have. Plus all of the reliability ones I mentioned in the beginning, that is a pretty good pitch. We just talked about how Rust offers several safety features like memory, safety, error handling, and a type system. This is because reliable is not about one thing, but several things at once. This is where I need to mention representing sponsor, Antisysysys. Like the designers of Rust, Antisysys
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I'd also like to mention two conferences this year, while I'll be talking and where we can also meet. On the 4th of June, I'll be doing a keynote at Craft Conference in Gudevesh, Hungary. This conference is one of the very best ones in Europe focused on software craftsmanship, and one where I'm a returning speaker. For more details, check out Craft-Conf.com. And on the 15th and 16th of September, I'll be doing a keynote at LDX3 in New York.
This is a festival for modern engineering leadership. Last year, I was at LDX3 in London, and so I'm excited to be back this time in New York. For more details about this conference, head to lead.com. If you'll be at either of them, I'll see you there. And with this, let's get back to Rust and Alice.
I wanted to ask why Rust is getting so popular, but I think we're starting to answer this question, right? I think where Rust is really unique is in the combination of things. So on one hand, it doesn't have a garbage collector, and it's usable in low-level context, like the Linux kernel or firmware, whatever. Why is it a good or a bad thing to have a garbage collector? Java has a garbage collector, C-sharp has a garbage collector.
So a garbage collector says, once you've done using your objects, there's going to be a little piece of code that checks all of your objects and says, this is not used anymore, and then it cleans it up. Whereas in languages like Rust or C++, the variable is cleaned up at the end of the scope when it goes out of scope. And in the other one, they have to detect afterwards. And this kind of little piece of code that runs every so often to check all your objects. For embedded use cases, this might simply be not possible or unacceptable. The performance overhead, the fact that you will not be able to
control the memory as much. Even for a backend, it can be a problem, because if you have a request incoming right when it checks all of your objects, you have some latency spike where it takes much longer to reply. So that's one of the reasons it can be helpful in backend as well. For someone who has not yet seen Rust code, how would you describe it, how it compares to, for example, TypeScript? I mean, in many cases, Rust code is similar to many of the other languages.
It has braces. It's not like Python where you use indentation. It has braces. It has semicolons and so on. So it's pretty easy to read, even if you don't. If you know some other languages, you can look at it
and you can get a rough idea. Yeah, I think you'll figure it out. It's not that. It's not that far in. Rust has a learning curve on the side of the more difficult languages to learn. What do you see
doves typically struggle with, who are new to Rust and what are the things that just makes it click for them? I think the most tricky thing people run into is how should you put together your data structure? I mean, for your code, you can mostly do the same things as your kind of other languages. I mean, that's not entirely true, but the big thing is really the data structures. So if you have, I don't know what would be a good example. Let's say some sort of, okay, let's just say you have
an object for a book and it has an area of pages and then you have an object for each page. If I was writing TypeScript, I would probably have a book field in the page that references the book, and then the book, of course, also references the page. Right, so it's cyclic. So the book goes to the page, goes back to the book. And in Rust, you usually have to design your object so that they're not cyclic. It has to be a tree or a deck, if you know what I mean. Yeah, the direct is asynchronous.
So if you go out and actually start to use reference counting, it becomes possible to have cyclic objects with some kind of a second mention. But what people end up doing when they're learning the language is that they try to make cyclic objects without anything like that. And then it just doesn't work. And they're going to run into all sorts of problems in their code while they're constructing, they may be creating that thing. And then they get a compiler error, and then they try to change the code and they get a compiler again. But the thing that a lot of people struggle with is that
they keep trying to change the code when the solution is to change the struct. I can see how that's frustrating. Rust has another model that might be new for especially for people coming from language types of is Rust's ownership model. What is the ownership model? The ownership is just the idea that if you have a variable containing some object, then the object is only there. It's kind of exclusive.
So for example, if you have a variable, let a equals your string or whatever, and then you do let be equal to a, then this is a move. And so this means that using a afterwards is now a compiler error, because its contents have been moved away. And of course, this is important when we don't have a garbage collector, because then when b goes out of scope, it has to clean up the string. Now, if a was also valid, then when they both went out of scope, it would clean up the string twice, which is not legal in most other languages, the garbage collector takes care of this, a and b just go out of scope, do nothing. And then later it cleans up the string. But here, we actually have to do it when we go out of
scope. And the ownership model allows you to move from a to b, and then a becomes inactive or unusable and does not get cleaned up because it doesn't have a value to clean up anymore. And how does reference counting relate to all this? In Rust, we have a bunch of different types, which are essentially different kind of pointers. And one of the pointers is it's called arc and it's reference count. And so the idea is you have some objects somewhere, and then you have
an arc to the object. And what you can do is you can call clone on the arc and disincrement encounter, and now you have two arcs to the same underlying memory. So the object might be really big, but you have two arcs that share the same memory. And when they go out of scope, the counter is just decremented. And when the counter reaches zero, the object is cleaned up. So this is a way of
saying this object actually needs to be in multiple places. There's no one place that owns it. And so this way, you can use a counter to know how many owners are there. And then when the last owner goes away, it gets cleaned up. And then Rust also another thing that was using the borrow checker. So another
point of type we have in Rust is called the reference. And a reference is basically all it is that it's a point of the object. And that's it. So we do no checking at runtime. So of course, this means a compile time, we have to make sure that the last use of the reference has to be before the object goes out of scope. And creating a reference is called borrowing, right, the owner owns the value.
And now we have a borrow of the value, the reference. And the borrow checker checks that the reference is like the last use of the references before the object goes out of scope. So if you have to say, let's say you have an immutable reference, you're reading, then if you change the object, let's say it's in vector. So I have a immutable reference, I'm reading element five, and then I change the vector, I call clear. Then the borrow checker also ensures that you can't use the reference to object five afterwards. Yes, because now it has been as soon as you change it, it went
out of scope, it's now clear, right? Yeah, the way it works is that if there are mutable borrows, it ensures that the mutable borrow ends or starts before or after the previous borrows have ended, basically, so they don't know what happened. So you can only have one writer at the time, or you can have any number of readers, it checks that on the scope, like in a function. This concept is, is, is using it as someone who's not used Rust or Shred, it's very interesting. One thing I read is on forums, people complaining about fighting, so-called fighting the borrow checker, what can make a challenging when you write up some code that uses the object in a way that doesn't follow the rules I mentioned, that's a compiler error. And fighting the borrow checker is
when you can't get out of those compilers, I guess. I think a lot of the time this has to do with the struct. One common mistake I see is that if you have a struct with a reference in it, Rust kind of assumes that it can check the scope of that reference, like by just looking at a single function. But if you have your struct and you're passing it over functions, that it might not be possible to make that analysis. And so you just get a compiler error. And so in this case, the solution is maybe
to use a different pointer type. For example, the reference counterpoint type often solves this kind of book. So the solution is again to change the data structure. Yeah, I'm starting to understand why you mentioned that data structures were a place of learning, coming from other languages. Often times the solution seems to be just think about your data structures, understand them and do it in the Rust way, right? We talked about memory safety, but there is a keyword in Rust called unsafe. What does
this do? And in what cases do people typically use one that does it make sense to use? And why does it even exist? That's just a naive question from me. So let me begin with the what and let's take the why off to it. So the what is the unsafe is the escape hatch, essentially. So I explained
before how there are certain books where if your program has one of those books, that's usually a security vulnerability. What Rust ensures is that if you have no use of unsafe, then no matter how stupid your code is, you will never have one of those books. Now, if you do use unsafe, then there are still some guarantees, but it's a bit weaker because each unsafe operation that you can perform has a list of rules. And if you violate these rules, then you might end up with one of these bad books. But of course, if you don't, then you it's okay. And it's interesting to point
out here that unsafe does not disable the borrow check or anything like that. It just gives you a few more operations you can perform that are not safe in general. And so you have to check yourself. Yeah, this is actually okay. In this particular case to, I mean, let's take the back to example again.
Normally, when you index index five, it will say, Oh, let me check the length. So if the length is at least six, yeah, because it's our zero, then it's okay. Otherwise, you gotta crash. But maybe you're writing some super high performance code and you want to avoid this if you want to avoid this check, or if you're in a loop every time. So unsafe will just avoid checks. May that be as if runtime
or compile time checks are both what I would say here is that Vectar has two different ways of getting a value. There's the normal bracket operator will use for other languages, which will do the check and crash a program if you get it wrong. But there's another function called get on checked. And so if you do write wecked that get on checked five, then it will give you element five without checking the length. And this function, like in the function signature, it says unsafe, FN, that's the function signature. And so you can call this function from an unsafe block.
Got it. And so all that the unsafe block that you do is call functions mark on safe. And then in practice, or sensible use cases of unsafe, is it usually to do with high performance code typically? Or like what case have you seen which are like legitimate? This is a great use case for unsafe. So usually it will never show up in say a back end server, you would have zero users
generally when unsafe is used, it's to add new features to the language. Let's say the language didn't have a vector. The language still has a function to allocate memory, a function to free memory, a function to read at this point address. Then you could write struck back the point is here and this is a raw pointer. So it's unsafe to use the length is this the capacity is this. So I might
and then you can write your little API. Of course, the fields are private. So you can't access them from outside the module. I mean, if you do wecked at length equal 20, just access the field that would be pretty bad. And so you can write your own vector API and using field privacy and good API design, you can add a vector to the language if it doesn't already exist. And unsafe, if encapsulated
properly in this kind of API that doesn't permit you to mess it up, then you can have a safe vector that you can use from safe code. And no matter what, how stupid the thing you do with that vector is it's not gonna do something bad. It's just gonna crash or whatever, check the length properly. As long as you design your API, right, you can add new language features by using unsafe. The other passive example would be to call into a C library. You can write a library that calls into
C and you can even have a safe API. And then you can enforce that you only call the C API in the right way. Can we talk about the Rust ecosystem, the broader ecosystem? And when it comes to the first thing that people come across and do myself is the crate ecosystem, Rust is package manager. What is crate and how does it compare to other package managers in like places like NPM or PIP and Python?
So crate is just the Rust word for a package. So it's just a package of your code. So the way it works is that Rust has a tool called cargo and cargo is kind of, it does a lot of stuff. It's actually creating a tool that's kind of all in one. So it will do it's both what you use to run your code, you do cargo run and it will compile your code. You have this thing called cargo tunnel,
where you specify your dependencies and other information about your crate. And when you do cargo run, it will download the dependencies to something called a registry, which is basically just a directory with all the crates you have downloaded. And you can also do cargo test, it will run all your tests, cargo dock, it will generate your dog. Cargo test will also run your dog test. That's even benchmarked and examples. So it does all the whole suite, so to say,
you don't need different tools to fetch dependencies and run your code and generate dogs. I think the biggest difference from something like pip would be that they're not installed to your machine. Right? With pip, you either install things globally or you have these virtual environments. So with cargo, it's all local, you just run cargo run and it's only local to this. The only thing that
shared is this registry, which is just to avoid downloading the same thing twice. You told me a funny anecdote about the historical and his reaction or what he told you about Rust and cargo. The first time I was at the Linux promise conference, at the very end, so Linux wasn't anywhere to see throughout the entire conference. But at the very end, at the social event, he showed up. And I went over to say hi, I mentioned I worked on Rust and immediately he started telling me about how he didn't like cargo. And so the reason for that is that cargo downloads code from the internet and runs it,
like any package manager. And he doesn't want any code in his computer to do that other than his distribution package manager. He doesn't trust anybody else to do that. In the old world, we're seeing more problems with vulnerabilities being injected into packages, just about after overtaking packages, they put in whatever code might be from crypto, which is the better part to security vulnerabilities. Does cargo have this problem as well, just like any package manager that is on the internet? I'm just in principle. Yeah. I mean, ultimately,
if you somehow got a hold of my keys to upload new Tokyo versions, you could upload them in this just one. I don't think we've had much problems with it compared to something like NPM, but I don't really know if we, I mean, it's a hard problem, right? It's hard problem. If somebody can impersonate the maintainer of a library, then I mean, I think they do do stuff like delete, to go squatting malicious crates and stuff like that. Where do you see the rust ecosystem being the most mature and the least mature right now? My opinion is that the least mature area is frontend.
There have been some attempts to compile rust to WebAssembly and then run it on the Web as a frontend as a replacement for TypeScript. But if I was writing a Web server, I would totally use rust for the backend and TypeScript for the frontend. I would not really go the WebAssembly route. On the other hand, for backend, I actually think it's a pretty great fit. And there's also stuff like command line tools. I think it's really, really great fit for that. And then of course, we have,
we are expanding into Linux and we are also expanding into a lot of embedded projects. And there are even projects that are like C code bases that are starting to say, hey, it's went into Linux. Maybe we should start using it too. Maybe we should have a memory, a sick language too. I know that Gator is talking about it. I know that CPython is talking about it.
There are probably others. QEMO maybe. Can we talk about how the language is built? Who builds Rust, what the process for for doing it? How does it compare to a project like Linux? I know it's not
a language, but it's still a large open source project. I mean, it's really an open source project. I mean, you may know that it originally originates from a Silla, but it's not a Massilla project anymore. So today, there's the Rust project, which has a bunch of different teams. There's the language team, which deals with the library API team, which decides on the API of the standard library. And these teams kind of go on it. It's the people who aren't these teams that run the
language. And one interesting difference compared to some other popular languages like Python or projects like Linux is they have a benevolent dictator for life. And Rust does not. How is this working? And how are decisions made when, especially when they're contagious or what if it could help for someone to just make a decision? Honestly, if the team doesn't sign off on it, it doesn't happen.
I mean, if something is really contentious or really big, it will probably end up being discussed at a conference, for example. So there's a conference called Rust Week where they have an event called the Rust All Hands where they're basically taking all of the Rust developers and putting them in one place. So if there was a problem like that, they would probably discuss it there. And how are these teams structured? So like you said, there's a compiler language, library and dev tools, at the very least, how do they define boundaries? Is there just a team kind of roughly defining them? And then
you just kind of agree. Because as I'm thinking at a corporate level, like as a company would run, there's typically teams are founded off and top down, leadership is a mandate, this will be this team that team, there's bottoms up happening, but oftentimes it's top down just because it's easier. But here, as I understand, there is no top down. It's people self organizing. Yeah, really, when it comes to the design of the language, the teams are really, that's really it.
Teams have been pretty good. As far as I've seen that delegating. So I've seen them sometimes say, we think this is a libs API decision and we will go with whatever libs API decides. One thing that is interesting to talk about is the RFC process. So there's a request for process.
RFC request for comment is the way the Rust project makes big decisions, but big ones, it's important to say. Basically, the way it works is let's say you have a language feature that's kind of big. For example, I had one called drives, which basically makes some types in the standard library less special. So I mean, sometimes people begin implementation already. But the idea is that you write the RFC first.
By the way, that's no different inside of like a Uber we had at RFC was in the same thing. Usually followed, but sometimes you kind of start to build it and just the idea is you write the the first. Yeah, I know. It just funny how it happens everywhere with engineers, I think, it's to build. You write this dark and it has a template. And I think it's actually a pretty good
template. The idea is the first section is I think motivation. The first one is summary. But the first and point one is motivation to explain why this feature and then I think they have two really interesting sections. They have the guide level explanation and the reference level explanation.
And what this is is that in the guide level explanation, you explain your feature as if you were writing a guide, as if the feature already existed. And in the reference level explanation, you explain your feature again as if it already existed. But as if it would be in the language reference instead of a tutorial. This is really interesting. Amazon does just relate to this when they ask people to build a feature, they have a press release. Like imagine if you announced this, I just love how like
both this and what you're saying it forces you to just think from a very different perspective, right from how people will use this feature. And then other sections, there's I think you mentioned rationale alternatives prior to future possibilities. Yeah, so that you know, you get to explain so rational and alternatives, I think it's a pretty important section because you get to answer all of the questions before they get asked and you get to explain why did you pick this design and that's not a lot of the sign. And I think that's usually a pretty big part of an I've seen. And then of course, it's good to look at what did C++ do and what can we do in the future as well.
And once you have the RFC, you send it out. What happens then? Well, somehow people get people to look at it. There is an IFC repository and you can open a pull request there with your markdown document with RFC and people can discuss it. You might also write up your docs on my else and call it the pre- RFC if it's not in the RFC directory, but it's kind of the same thing.
Let's say that the language team, it's a language team RFC and they're happy with it. So I said that I see was how the language makes big decisions. But then they actually use a process that comes up for all decisions essentially called the final comment period. And so the idea is they tell the bot to please start the approval process and then it will rate a comment on GitHub with a checkbox for every team member. And then team members check their own checkbox and once everybody from the team except for at most two have checked their checkbox, then the final comment period will begin, which is two weeks. Oh, so when it's only two checkboxes left, then two weeks to start. What's the rational
for this? This is very interesting. It's a story fact more like, I mean, you know, let's say that everybody checks that box immediately and then the two other people didn't get a chance to look at. So it's to make sure that everybody has a chance to see it. Yes, I understand. And also to keep things
moving at a sensible pace. So there's another part of the process, which is concerns team members can find a concern, which basically you pull through the process until it's resolved. And then once the two weeks pass, it's accepted. So that's essentially how the team makes decision. And this is not just I've sees if you have, I don't know, a pull request changing something in the reference, then the language team might say, Oh, we need to make sure that everybody's on board with this change. They'll tell the bot
to start an FTP on this random PR or some random issue or whatever it might be the same process applies. And then once let's say this is like language feature, KBRC accepted, we know what we're going to then the feature is just built, you start to open your pull request and get into language pretty much. But you put the feature behind a feature flag in Rust, we have this thing called nightly features, which basically means that you can't use it normally. But if you use the nightly build of the compiler, you can once you have your feature, I mean, you might begin. But you know, once you have your accepted RFC, you start submitting pull requests, you implement your feature, it gets merged, and people start using it experimentally on the nightly build. Yeah. And then at some point,
you might say, Okay, I think this feature is ready. And this is kind of a reason to mention, but we have come up with this idea of a stabilization report in the pull request that changed that removes the feature flag. We write up a little report saying, for example, how it's been used and explaining like, Oh, here are the dangerous edge cases here are the tests for each of the dangerous, so that kind of stuff. And then they use the FTP process again, who agreed to stabilize it, and then it's merged. And so now you have a feature without a feature flag.
Yeah. In the main branch, yes, between zero days and six weeks from that, there will be a beta release of the compiler, and it will be it will be in it. Yeah, it will be in it. And then six weeks later, the beta release becomes the next stable release. Okay, so like Russ has a strict six week release cycle, unlike with Linux, well, Linux also has a roughly more but here you just take the state stable branch, you're not doing any special. Yeah, and so we don't really have a concept
of beta features that are only available available on beta. You have a nightly, pretty much nightly, or people can get on to the latest branch, which is not yet cut. Yeah, the main purpose of beta is to test like you get six weeks to test the stable release. So hopefully, if there's any problems, we can fix them before it goes out into a stable release. And you mentioned that RFCs are only for large decisions that needs to be made, and you haven't written that many either just because they're large. What about smaller decisions that you also want to get consensus on? So here, there are a few
different ways to do it. So let's say you want to add a new function in the standard library or new type, then the library team actually has this thing called an ACP, an API change proposal, which is basically just an issue when get up. So you open your issue, you describe your API, describe what the interface is and explain why you should have it. And it's much smaller than an RFC would be. And then the library team can say, this is okay with us. And then you can implement
it on on-site or nightly. And then later, you can then stabilize it. And similarly, the compiler team has major change proposals. You need to say how it's called MCPs. What is going to confuse a lot of people outside of we're not inside of Rust. Yeah, it is what it is. We offer the small
small of eTils. Yeah, even though it's called major, right? It's big enough that they need to put up an issue, but not big enough to need an RFC. And for the compiler team, the classic example would be a new compiler flag. Now, Rust has new new new builds every six weeks, right?
But it also has editions. There was one in 2015, 2018, 2021, 2024. What are editions? So the thing about editions that is different from versions is that if you're using version 1.90 at the compiler, everything is using that version. But different crates can use different editions.
And so I might have a crate using the 2025 edition of the language. And I can keep using that forever, because Rust has a really, really high stack words compatibility guarantee. So you write all of your code and the guarantee is that it's got a key working forever. That's the idea. Anyway, editions are basically the way that Rust makes breaking changes without breaking people, because they might change the syntax of the language. For example, async await was added to one edition.
And so code using the old edition can't use async await. There you can have a variable called async if you want, let async equal five. And then in the new edition, you can't. But you can still mix and match code written in different editions. So they work together. Oh, interesting. So I might
have a library written in the 2021 edition, and you can write your library in 2024 edition or your binary project. And then you can still use my library. Why do you think Rust decided on editions, which feels a bit more confusing to me as opposed to versions, like when I look at Java's versions or PHP's versions or even Ruby on Rails versions, you know, there's always a major number. And I might be wrong, but it sounds to me that an edition is almost inequivalent of a major version of the other languages is that putting it correctly or am I missing some details here? Really, the big idea is to say we want the old code to continue working, but we still want to change the language. And so the difference from other kinds of versions of languages, I mean,
Python two, which in Python three comes to mind, is that you can totally mix and match in any way you want. You are a language team advisor, or using the became one, what is a language team advisor? And what do you do as part of this role? We have, of course, the language team, which they have meetings every week, and they do a lot of stuff. And so on and so forth. The
language team advisor role is a way to be part of the language team light in some sense. So you're someone that they've said, okay, we trust this person's opinion. But you don't necessarily go to every single meeting, like there's no checkbox for you on an FTP. So you can still file a concern. So yeah, it's really a way to participate in or help the language team without full membership and full membership might entail a lot of things, right? For example, for me, it would entail going
to meetings every Wednesday evening instead of like when I would normally have dinner. From your observation, what is the corporate influence like on Rust in the sense that when I talked with Greg Cage, he was telling me that in practice, about 80% of the frequent Linux contributors are typically employed by a company which sees value in adding their features or maintaining their features. And Linux, which turns out to be like a nice kind of like a symbiosis in some ways for Rust, the people working on it, are they usually paid by their employers? Like you are, I'm sure there's people who are just every now and then contributing with people who are spending more time on this, do you see a pattern of corporations actually supporting this or is there a foundation that also supports people to work on this full time or close to full time? I would say here that the Linux kernel is truly unique in this particular aspect in that they have thousands of contributors doing it on work time. I actually think that the Rust project is doing pretty well at having people
do it and get paid for it, like by their employer, but it's nowhere near to the same extent as the Linux kernel. The Rust project also has a few other interesting things. So the Rust Foundation have some grants that allow, I mean, for example, if you're a student and you want to work on something, you might be able to get a grant, some money from the Rust Foundation. I think that's a super cool thing that the Foundation is doing. Especially I think getting people and most students involved are the people who would find it harder or more daunting to get a mobile project like this.
Speaking of which, for first, offer engineer who would be interested to contribute to the Rust ecosystem, what would your suggestion be in terms of both resources or ways to get started? I mean, obviously you can go to the issue tracker and look for issues that interest you. I think that often it's, I mean, the best way to contribute something is if you have something you want to change about it. I think that's often a pretty good starting point. So if you wanted to contribute to the Rust language itself, Rust does a lot of it's stuff on something called SULIP, which is a chat server where people talk and you could go there and talk to people. So the Rust or Linux project has a pretty nice
contributing page. So Rust for Linux.com and that's a contributing page there. With for one, there are a few different drivers you might be able to contribute to and they have links to the issue tracker there. Another thing that's really cool is you can contribute to the Linux kernel without contributing to the Linux kernel, right? Because you might take a Rust language feature we need and implement it. And now you contribute to the Linux kernel indirectly.
Or maybe you want to work on the Rust in GCC project and help move that forward. And so I think there are a lot of different projects, other than the Linux kernel that would help Rust in the Linux kernel a lot to contribute there. Can we talk a little bit about Rust in the Linux kernel, on how that has evolved, how you got involved in writing Rust in the Linux kernel? And have you seen the approach of especially Linux kernel devs, the change or soften towards Rust? Because I know it was very heated topic earlier on Linux has this conference called Linux Glamas, which, you know, as part of my work on Rust for the Linux kernel, I've been going through for the past few years. And one thing I think has been really obvious is every time I've gone, you can say,
things have totally changed since last year. I've experienced this like four times in a row. That's kind of pretty cool. Yeah, I think there's really a lot of stuff that's happening. I mean, one year I might go and people think, oh, that's some nice little thing you have there, right? And
then the next year, now they have Rust code in their system. It kind of keeps going. The most recent Linux plumbers from December 2025 was there, the big news were that at the Linux kernel maintain a summit, we agreed that Rust is no longer experimental in the kernel. That was really big for us compared to the previous year. So now that means that it's official, like Rust has the same status as C, which is the language that the kernel is written in, right? I guess. Well, not the same
status, but not being experimental. It clearly marks that it's more stable. Experimental sounds like it's not a stable. Basically, we've proved this is going to work. I mean, based on what you've laid out with just with memory safety, and of course, being able to use unsafe when you need to, that already shows a lot of, I guess, promise. Plus there's some regulation as well, right? There's
I think the U.S. Department of Defense passed some regulations saying that they will not allow their agencies to use non-memory safe languages for the concern of security vulnerabilities. And this would practically mean that Rust and other memory safe languages could be used, but CC++ or maybe one day systems that are built in this one might see larger scrutiny. Yeah, there have been different stuff like that from multiple different governments, right? These governments are saying you guys are using C or C++ in this project, and it's causing an unacceptable amount of memory safe vulnerabilities that simply don't happen if you just don't.
So what if you didn't do that? In this conversation, we managed to go for a very long time without even mentioning AI once, which given where the world right now is and how these tools are spreading, that's very impressive. I was interested. Do you use any of the AI tools for your day-to-day work, building Tokyo, contributing to Rust projects? Have you found a need for them at all?
So I have been trying to use them. Honestly, I'm still learning how to use these tools, but I have used them. I quite like the German and I command line interface. I think it's pretty neat. These tools are pretty proficient at outputting code, or giving a prompt and putting out code.
But in your day-to-day work, how much code do you actually type as opposed to reviewing code, thinking about what to do, making a plan? As we're talking about the ARF, for example, the ARF C process, my sense was most of that was thinking about what to build, getting a consensus, making sure it's right. And it almost sounded like the actual code itself would be the, I don't know, lesser of course, there's a lot of work involved with you too. I mean, the actual time spent will probably be less than everything else around it. I think it's still an important part of the process. I mean, a lot of people talk about that.
When you use AI, it's really important to write tests and that kind of thing, because then the AI is actually able to tell if it did it right. I explained the story from before about how I refactoring something. I just told it was a compiler told me. I think the same kind of principle applies with agents in that they can talk to the compiler. It will tell them what to fix.
I guess this could be a case of what we'll see, but Rust could be a pretty promising candidate for to use for agents because they can get more feedback and it's harder to ship certain type of bugs or maybe impossible to have certain type of bugs. Yeah, I think there is an aspect of that. For places like the Linux kernel where, I mean, correctness is extremely important, reliable is very important. There's already multiple layers of human review, which is in place. Do you see potential for AI generated code to prove helpful?
Somewhere like, actually truly helpful. Like, again, assuming that these things can generate, you know, as per specification or as per what you need or could this be a place where like, it might be one of the places where we might not need that much because it already feels the to me, it feels like a place where there's a lot of people coming in, contributing and there's there's a reason that change can propagate slower. When I was at the Linux kernel maintainers summit, one of the topics that came up was using AI for code review. And there were some people there who had, for example, set up bots that would say when you send an email to the mailing list, it would feed it into an AI agent, which would leave a review, that kind of stuff. And for example, Linux and others were talking about how these reviews were actually really impressive for kernel code, at least what's being discussed in the kernel community that kind of use case seems like something people are excited about.
And it sounds like this would not be a replacement, obviously, but just one more way to get feedback, maybe doing quicker and just an additional safety net, if you will, right? I mean, that's the thing with memory safety, right? You make some sort of trivial mistake. It's not some complex thing. It's just, if you make some trivial mistake and there's a Gillian places you could make it. So even if even if you're a really good programmer and only make it
0.1% of the time or whatever, it's still gonna have, right? And so if they are, I can catch a lot of those, then, you know, that's pretty good. Well, I guess some creative use cases could be, for example, their tests are a big thing, but AI might be able to help figure out if there's edge cases missing again, if the language itself is not supported. But there could be, what I understand, and there's, there could be a lot of potential to add more safety nets that do not exist today. I think that's right.
I like this approach. So this is one of the first conversations I'm having where we're talking about AI, where we're talking about how to increase quality with AI, because then again, in startups or whoever's building, there's a lot of talk about how they can make it faster, faster restoration. And there's usually quality trade off that we usually do not talk about. But I love that we're actually talking about the things that can increase quality or at least keep it at the same level. I mean, I have actually written a few patches with AI myself. It worked okay.
Some, I mean, it definitely required my review before sending it out to the list. It really did, sometimes. But you know, and other place I remember using it was I had this commit that made mind of faster in some way. And one of the review comments I had received was, hey, can you run a benchmark? That's, oh my God, I have to write a benchmark. But then I got the AI to benchmark it for me.
And what it did, what it actually went and found an existing benchmark and modified it a little bit in a quite clever way. And then it ran it for me and then it wrote a Python script to analyze the text file with the numbers and presented it in a nice table. So it sounds like this was toil work that you could have done, but you might have not done as good of a word because you might have not found that you tell you might not figure it out to do that. I mean, at least in that instance, it'd take me time if nothing else. For a senior engineer who would like to learn Rust or just build with it, what would you suggest them to be to get started? Of course, the first AI might be one of the things which makes it a lot
easier just to get started. But if you would like to learn what do you recommend for people who actually want to become professional of the language? The one I would say that the Rust book, which is it's on the official Rust website, it's actually really good. You don't have to. It's really available online.
Rust has this idea of calling tutorials for books, even though they're online, which is kind of funny. But anyways, I think the Rust book is really good. Other than that, I think honestly, the way you learn a language is you have a project. You implement some sort of project with it. I mean, maybe some sort of web server or something.
And one more thing on AI. So it's easy to get started with languages these days because you can just prompt the AI to write this or that. In the case of Rust, do you think that could create a false sense of understanding, especially we talked about the importance of understanding structures of understanding compiler issues, which are there for a reason tools could just like generate through this and create code that that runs. Yeah, it's totally a danger. I recently tried using it for something where I guess I was not writing Rust code. I was writing make files. I wanted to add some support in the little kernel build system
for some feature. And it went into the make file and added the Rust flags necessary to do it. But then I looked at the code and it was it had added the necessary build flags. But to the seaside was passing a few more flags, which were not required per se, but they were there for a reason. And it had just ignored them. Any human looking at this would be like,
why did you add Rust versions of all the flags? What is your favorite Rust feature if there is one? I'm currently working on a new feature, which I think is really exciting. It's something that we ran into in the Linux kernel, where we needed in place initialization the ability to construct values while knowing whether being constructed so they don't get moved afterwards. I'm pretty excited about our work to put that into the language, but it's very much ongoing. I think that's
pretty cool stuff. And as closing, what are what are books you would recommend that you enjoyed and why? I already mentioned the official Rust book. I also think that so John Gingsett has an other book that I think is really good. And this book is kind of aimed at the intermediate Rust developer, the Rust developer who has gotten some Rust experience, but wants to go further.
I think that's also a pretty good book for that audience. Some other resources, which are not books, but which I think are also really good is there's this thing called Rustlings. And the idea is that they give you some unfinished Rust code and your task is to finish it. Oh, nice. And I think that's a pretty cool way to learn the language as well.
Awesome. Alice, thank you so much for this. This was really interesting and I've learned a bunch. Thank you for having me on. I hope you enjoyed getting into the details about Rust as much as I did.
One thing I appreciated talking about is how deliberately Rust seems to have been designed around the question, what mistakes do programmers actually keep making, and how do we eliminate those mistakes? A few examples include memory safety, not having a null, and the errors being values that you cannot ignore. The documentation example is also an interesting one. Documentation tests or doc tests are automatically run as tests. If your example breaks, then your build breaks.
This is the first time I've heard this clever idea implemented in a way that's easy to use in a language. Finally, the question on why Rust is becoming a soul pop there might be because it's in a category that did not exist before, while language that's reliable and also performant at the same time. This makes it usable for high performance computer cases like kernel work, while also being a good alternative for higher level back-end languages. Do check out the show notes for related the pragmatic and your deep dives that go even deeper into back-end topics and stories of building languages like Kotlin and Swift. If you've enjoyed this podcast, please do subscribe to our favorite podcast platform and on YouTube. A special thank you if you also leave a rating on
the show. Thanks and see you in the next one.