So there's this guy you may have heard of called Ryan Fleury who makes the RAD debugger for Epic. The whole thing is made with 278k lines of C and is built as a unity build (all the code is included into one file that is compiled as a single translation unit). On a decent windows machine it takes 1.5 seconds to do a clean compile. This seems like a clear case-study that compilation can be incredibly fast and makes me wonder why other languages like Rust and Swift can't just do something similar to achieve similar speeds.
The more your compiler does for you at build time, the longer it will take to build, it's that simple.
Go has sub-second build times even on massive code-bases. Why? because it doesn't do a lot at build time. It has a simple module system, (relatively) simple type system, and leaves a whole bunch of stuff be handled by the GC at runtime. It's great for its intended use case.
When you have things like macros, advanced type systems, and want robustness guarantees at build time.. then you have to pay for that.
I think this is mostly a myth. If you look at Rust compiler benchmarks, while typechecking isn't _free_ it's also not the bottleneck.
A big reason that amalgamation builds of C and C++ can absolutely fly is because they aren't reparsing headers and generating exactly one object file so the linker has no work to do.
Once you add static linking to the toolchain (in all of its forms) things get really fucking slow.
Codegen is also a problem. Rust tends to generate a lot more code than C or C++, so while the compiler is done doing most of its typechecking work, the backend and assembler has a lot of things to chuck through.
Not only does it generate more code, the initially generated code before optimizations is also often worse. For example, heavy use of iterators means a ton of generics being instantiated and a ton of call code for setting up and tearing down call frames. This gets heavily inlined and flattened out, so in the end it's extremely well-optimized, but it's a lot of work for the compiler. Writing it all out classically with for loops and ifs is possible, but it's harder to read.
The swift compiler is definitely bottle necked by type checking. For example, as a language requirement, generic types are left more or less in-tact after compilation. They are type checked independent of what is happening. This is unlike C++ templates which are effectively copy-pasting the resolved type with the generic for every occurrence of type resolution.
This has tradeoffs: increased ABI stability at the cost of longer compile times.
A lot can be done by the programmer to mitigate slow builds in Swift. Breaking up long expressions into smaller ones and using explicit types where type inference is expensive for example.
I’d like to see tooling for this to pinpoint bottlenecks - it’s not always obvious what’s making builds slow.
That the type system is responsible for rust's slow builds is a common and enduring myth. `cargo check` (which just does typechecking) is actually usually pretty fast. Most of the build time is spent in the code generation phase. Some macros do cause problems as you mention, since the code that contains the macro must be compiled before the code that uses it, so they reduce parallelism.
> Most of the build time is spent in the code generation phase.
I can believe that, but even so it's caused by the type system monomorphising everything. When it use qsort from libc, you are using per-compiled code from a library. When you use slice::sort(), you get custom assembler compiled to suit your application. Thus, there is a lot more code generation going on, and that is caused by the tradeoffs they've made with the type system.
Rusts approach give you all sorts of advantages, like fast code and strong compile time type checking. But it comes with warts too, like fat binaries, and a bug in slice::sort() can't be fixed by just shipping of the std dynamic library, because there is no such library. It's been recompiled, just for you.
FWIW, modern C++ (like boost) that places everything in templates in .h files suffers from the same problem. If Swift suffers from it too, I'd wager it's the same cause.
It's partly by the type system. You can implement a std::sort (or slice::sort()) that just delegates to qsort or a qsort-like implementation and have roughly the same compile time performance as just using qsort straight.
But not having to is a win, as the monomorphised sorts are just much faster at runtime than having to do an indirect call for each comparison.
I just ran cargo check on nushell, and it took a minute and a half. I didn't time how long it took to compile, maybe five minutes earlier today? So I would call it faster, but still not fast.
I was all excited to conduct the "cargo check; mrustc; cc" is 100x faster experiment, but I think at best, the multiple is going to be pretty small.
Did you do it from a clean build? In that case, it's actually a slightly misleading metric, since rust needs to actually compile macros in order to typecheck code that uses them. (And therefore must also compile all the code that the macro depends on.) My bad for suggesting it, haha. Incremental cargo check is often a better way of seeing how long typechecking takes, since usually you haven't modified any macros that will need to be recompiled. On my project at work, incremental cargo check takes `1.71s`.
Yes but I'd also add that Go specifically does not optimize well.
The compiler is optimized for compilation speed, not runtime performance. Generally speaking, it does well enough. Especially because it's usecase is often applications where "good enough" is good enough (IE, IO heavy applications).
You can see that with "gccgo". Slower to compile, faster to run.
Is gccgo really faster? Last time I looked it looked like it was abandoned (stuck at go 1.18, had no generics support) and was not really faster than the "actual" compiler.
Digging around, looks like it's workload dependent.
For pure computational workloads, it'll be faster. However, anything with heavy allocation will suffer as apparently the gccgo GC and GC related optimizations aren't as good as cgo's.
Not really. The root reason behind Go's fast compilation is that it was specifically designed to compile fast. The implementation details are just a natural consequence of that design decision.
Since fast compilation was a goal, every part of the design was looked at through a rough "can this be a horrible bottleneck?", and discarded if so. For example, the import (package) system was designed to avoid the horrible, inefficient mess of C++. It's obvious that you never want to compile the same package more than once and that you need to support parallel package compilation. These may be blindingly obvious, but if you don't think about compilation speed at design time, you'll get this wrong and will never be able to fix it.
As far as optimizations vs compile speed goes, it's just a simple case of diminishing returns. Since Rust has maximum possible perfomance as a goal, it's forced to go well into the diminishing returns territory, sacrificing a ton of compile speed for minor performance improvements. Go has far more modest performance goals, so it can get 80% of the possible performance for only 20% of the compile cost. Rust can't afford to relax its stance because it's competing with languages like C++, and to some extent C, that are willing to go to any length to squeeze out an extra 1% of perfomance.
Dlang compilers does more than any C++ compiler (metaprogramming, a better template system and compile time execution) and it's hugely faster. Language syntax design has a role here.
This is sometimes called amalgamation and you can do it Rust as well. Either manually or with tools. The point is that apart from very specific niches it is just not a practical approach.
It's not that it can't be done but that it usually is not worth the hassle and our goal should be for compilation to be fast despite not everything being in one file.
Turbo Pascal is a prime example for a compiler that won the market not least because of its - for the time - outstanding compilation speed.
In the same vein, a language can be designed for fast compilation. Pascal in general was designed for single-pass compilation which made it naturally fast. All the necessary forward declarations were a pain though and the victory of languages that are not designed for single-pass compilation proofs that while doable it was not worth it in the end.
Because Russt and Swift are doing much more work than a C compiler would? The analysis necessary for the borrow checker is not free, likewise with a lot of other compile-time checks in both languages. C can be fast because it effectively does no compile-time checking of things beyond basic syntax so you can call foo(char) with foo(int) and other unholy things.
The borrow checker is usually a blip on the overall graph of compilation time.
The overall principle is sound though: it's true that doing some work is more than doing no work. But the borrow checker and other safety checks are not the root of compile time performance in Rust.
While the borrow checker is one big difference, it's certainly not the only thing the rust compiler offers on top of C that takes more work.
Stuff like inserting bounds checking puts more work on the optimization passes and codegen backend as it simply has to deal with more instructions. And that then puts more symbols and larger sections in the input to the linker, slowing that down. Even if the frontend "proves" it's unnecessary that calculation isn't free. Many of those features are related to "safety" due to the goals of the language. I doubt the syntax itself really makes much of a difference as the parser isn't normally high on the profiled times either.
Generally it provides stricter checks that are normally punted to a linter tool in the c/c++ world - and nobody has accused clang-tidy of being fast :P
It truly is not about bounds checks. Index lookups are rare in practical Rust code, and the amount of code generated from them is miniscule.
But it _is_ about the sheer volume of stuff passed to LLVM, as you say, which comes from a couple of places, mostly related to monomorphization (generics), but also many calls to tiny inlined functions. Incidentally, this is also what makes many "modern" C++ projects slow to compile.
In my experience, similarly sized Rust and C++ projects seem to see similar compilation times. Sometimes C++ wins due to better parallelization (translation units in Rust are crates, not source files).
These languages do more at compile time, yes. However, I learned from Ryan's discord server that he did a unity build in a C++ codebase and got similar results (just a few seconds slower than the C code). Also, you could see in the article that most of the time was being spent in LLVM and linking. With a unity build, you nearly cut out link step entirely. Rust and Swift do some sophisticated things (hinley-milner, generics, etc.) but I have my doubts that those things cause the most slowdown.
That’s not a good example. Foo(int) is analyzed by compiler and a type conversion is inserted.
The language spec might be bad, but this isn’t letting the compiler cut corners.
This explanation gets repeated over and over again in discussions about the speed of the Rust compiler, but apart from rare pathological cases, the majority of time in a release build is not spent doing compile-time checks, but in LLVM. Rust has zero-cost abstractions, but the zero-cost refers to runtime, sadly there's a lot of junk generated at compile-time that LLVM has to work to remove. Which is does, very well, but at cost of slower compilation.
Well, zero-cost abstractions are still abstractions. It’s not junk per-se, but things that will be optimized out if the IR has enough information to safely do so, so basically lots of extra metadata to actually prove to LLVM that these things are safe.
You can address the junk problem manually by having generic functions delegate as much of their work as possible to non-generic or "less" generic functions (Where a "less" generic function is one that depends only on a known subset of type traits, such as size or alignment. Then delegating can help the compiler generate fewer redundant copies of your code, even if it can't avoid code monomorphization altogether.)
Probably, but it's the kind of thing that needs a lot of fairly significant overhauls in the compiler architecture to really move the needle on, as far as I understand.
I encountered one project in 2000-th with few dozens of KLoC in C++. It compiled in a fraction of a second on old computer. My hello world code with Boost took few seconds to compile. So it's not just about language, it's about structuring your code and using features with heavy compilation cost. I'm pretty sure that you can write Doom with C macros and it won't be fast. I'm also pretty sure, that you can write Rust code in a way to compile very fast.
My anecdata would be that the average C++ developer puts includes inside of every header file which includes more headers to the point where everything is including everything else and a single .cpp file draws huge swaths of unnecessary code in and the project takes eons to compile on a fast computer.
That's my 2000s development experience. Fortunately I've spent a good chunk of the 2010s and most of the 2020s using other languages.
The classic XKCD compilation comic exists for a reason.
I'd be very interested to see a list of features/patterns and the cost that they incur on the compiler. Ideally, people should be able to use the whole language without having to wait so long for the result.
Templates as one single feature can be hugely variable. Its effect on compilation time can be unmeasurable. Or you can easily write a few dozen lines that will take hours to compile.
So there are few distinctive patterns I observed in that project. Please note that many of those patterns are considered anti-patterns by many people, so I don't necessarily suggest to use them.
1. Use pointers and do not include header file for class, if you need pointer to that class. I think that's a pretty established pattern in C++. So if you want to declare pointer to a class in your header, you just write `class SomeClass;` instead of `#include "SomeClass.hpp"`.
2. Do not use STL or IOstreams. That project used only libc and POSIX API. I know that author really hated STL and considered it a huge mistake to be included to the standard language.
3. Avoid generic templates unless absolutely necessary. Templates force you to write your code in header file, so it'll be parsed multiple times for every include, compiled to multiple copies, etc. And even when you use templates, try to split the class to generic and non-generic part, so some code could be moved from header to source. Generally prefer run-time polymorphism to generic compile-time polymorphism.
I don't think it's interesting to observe that C code can be compiled quickly (so can Go, a language designed specifically for fast compilation). It's not a problem intrinsic to compilation; the interesting hard problem is to make Rust's semantics compile quickly. This is a FAQ on the Rust website.
I bet that if you take those 278k lines of code and rewrite them in simple Rust, without using generics, or macros, and using a single crate, without dependencies, you could achieve very similar compile times. The Rust compiler can be very fast if the code is simple. It's when you have dependencies and heavy abstractions (macros, generics, traits, deep dependency trees) that things become slow.
I'm curious about that point you made about dependencies. This Rust project (https://github.com/microsoft/edit) is made with essentially no dependencies, is 17,426 lines of code, and on an M4 Max it compiles in 1.83s debug and 5.40s release. The code seems pretty simple as well.
Edit: Note also that this is 10k more lines than the OP's project. This certainly makes those deps suspicious.
The 'essentially no dependencies' isn't entirely true. It depends on the 'windows' crate, which is Microsoft's auto-generated Win32 bindings. The 'windows' crate is huge, and would be leading to hundreds of thousands of LoC being pulled in.
There's some other dependencies in there that are only used when building for test/benchmarking like serde, zstd, and criterion. You would need to be certain you're building only the library and not the test harness to be sure those aren't being built too.
The borrow checker is really not that expensive. On a random example, a release build of the regex crate, I see <1% of time spent in borrowck. >80% is spent in codegen and LLVM.
Again, as this been often repeated, and backed up with data, the borrow-checker is a tiny fraction of a Rust apps build time, the biggest chunk of time is spent in LLVM.
I guess you can do that, but if for some reason you needed to compile separately, (suppose you sell the system to a third party to a client, and they need to modify module 1, module 2 and the main loop.)
It would be pretty trivial to remove some #include "module3.c" lines and add some -o module3 options to the compiler. Right?
I'm not sure what Rust or docker have to do with this basic issue, it just feels like young blood attempting 2020 solutions before exploring 1970 solutions.
Every claim I've seen about unity builds being fast just never rings true to me. I just downloaded the rad debugger and ran the build script on a 7950x (about as fast as you can get). A debug build took 5s, a release build 34s with either gcc or clang.
Maybe it's a MSVC thing - it does seem to have some multi-threading stuff. In any case raddbg non-clean builds take longer than any of my rust projects.
I use unity builds day in day out. The speed up is an order of magnitude on a 2m+ LOC project.
If you want to see the difference download unreal engine and compile the editor with and without unity builds enabled.
My experience has been the polar opposite of yours - similar size rust projects are an order of magnitude slower than C++ ones. Could you share an example of a project to compare with?
There's also Jonathan Blow's jai where he routinely builds an entire game from scratch in a few seconds (hopefully public beta will be released by the end of this year).
That "just" was too flippant. My bad. What I meant to convey is "hey, there's some fast compiling going on here and it wasn't that hard to pull off. Can we at least take a look at why that is and maybe do the same thing?".
> "hey, there's some fast compiling going on here and it wasn't that hard to pull off. Can we at least take a look at why that is and maybe do the same thing?".
Do you really believe that nobody over the course of Rust's lifetime has ever taken a look at C compilers and thought about if techniques they use could apply to the Rust compiler?
Rust and C have differences around compilation units: Rust's already tend to be much larger than C on average, because the entire crate (aka tree of modules) is the compilation unit in Rust, as opposed to the file-based (okay not if you're on some weird architecture) compilation unit of C.
Unity builds are useful for C programs because they tend to reduce header processing overhead, whereas Rust does not have the preprocessor or header files at all.
They also can help with reducing the number of object files (down to one from many), so that the linker has less work to do, this is already sort of done (though not to literally one) due to what I mentioned above.
In general, the conventional advice is to do the exact opposite: breaking large Rust projects into more, smaller compilation units can help do less "spurious" rebuilding, so smaller changes have less overall impact.
Basically, Rust's compile time issues lie elsewhere.
Can you explain why a unity build would help? Conventional wisdom is that Rust compilation is slow in part because it has too few translation units (one per crate, plus codegen units which only sometimes work), not too many.
> makes me wonder why other languages like Rust and Swift can't just do something similar to achieve similar speeds.
One of the primary features of Rust is the extensive compile-time checking. Monomorphization is also a complex operation, which is not exclusive to Rust.
C compile times should be very fast because it's a relatively low-level language.
On the grand scale of programming languages and their compile-time complexity, C code is closer to assembly language than modern languages like Rust or Swift.
Rust is doing a lot more under the hood. C doesn't track variable lifetimes, ownership, types, generics, handle dependency management, or handle compile-time execution (beyond the limited language that is the pre-compiler). The rust compiler also makes intelligent (scary intelligent!) suggestions when you've made a mistake: it needs a lot of context to be able to do that.
The rust compiler is actually pretty fast for all the work it's doing. It's just an absolutely insane amount of additional work. You shouldn't expect it to compile as fast as C.
I’m glad that Go went the other way around: compilation speed over optimization.
For the kind of work I do — writing servers, networking, and glue code — fast compilation is absolutely paramount. At the same time, I want some type safety, but not the overly obnoxious kind that won’t let me sloppily prototype. Also, the GC helps. So I’ll gladly pay the price. Not having to deal with sigil soup is another plus point.
I guess Google’s years of experience led to the conclusion that, for software development to scale, a simple type system, GC, and wicked fast compilation speed are more important than raw runtime throughput and semantic correctness. Given the amount of networking and large - scale infrastructure software written in Go, I think they absolutely nailed it.
But of course there are places where GC can’t be tolerated or correctness matters more than development speed. But I don’t work in that arena and am quite happy with the tradeoffs that Go made.
> fast compilation is absolutely paramount. At the same time, I want some type safety, but not the overly obnoxious kind that won’t let me sloppily prototype. Also, the GC helps
Well, that point in the design space was already occupied by Java which also has extremely fast builds. Go exists primarily because the designers wanted to make a new programming language, as far as I can tell. It has some nice implementation aspects but it picked up its users mostly from the Python/Ruby/JS world rather than C/C++/Java, which was the original target market they had in mind (i.e. Google servers). Scripting language users were in the market for a language that had a type system but not one that was too advanced, and which kept the scripting "feel" of very fast turnaround times. But not Java because that was old and unhip, and all the interesting intellectual space like writing libs/conf talks was camped on already.
Java still had slow startup and warmup time circa 2005-2007, on the order of 1-3 seconds for hello world and quite a bit more for real apps. That is horrendous for anything CLI based.
And you left out classloader/classpath/JAR dependency hell, which was horrid circa late 90s/early 2000s...and I'm guessing was still a struggle when Go really started development. Especially at Google's scale.
Don't get me wrong, Java has come a long way and is a fine language and the JVM is fantastic. But the java of 2025 is not the same as mid-to-late 2000s.
You can have the best of both worlds: A fast, but sloppy compiler and slow, but thorough checkers/linters. I think it's ideal that way, but rust seems to have chosen to needlessly combine both actions into one.
That is exactly what go was meant for and there is nothing better than picking the right tool for the job. The only foot gun I have seen people run into is parallelism with mutable shared state through channels can be subtly and exploitably wrong. I don't feel like most people use channels like that though? I use rust because that isn't the job I have. I usually have to cramb slow algorithms into slower hardware, and the problems are usually almost but not quite embarrassingly parallel.
I think a lot of the materials that the Go folks put out in the early days encourage a very channel-heavy style of programming that leads to extremely bad places.
Nowadays the culture seems to have evolved a bit. I now go into high alert mode if I see a channel cross a function boundary or a goroutine that wasn't created via errgroup or similar.
People also seem to have chilled out about the "share by communicating" thing. It's usually better to just use a mutex and I think people recognise that now.
What are obnoxious types? Types either represent the data correctly or not. I think you can force types to shut up the compiler in any language including Haskell, Idris, PureScript...
I'd say you already get like 70% of the benefit of a type system with just the basic "you can't pass an int where string is expected". Being able to define your own types based on the basic ones, like "type Email string", so it's no longer possible to pass a "string" where "Email" is expected gets you to 80%. Add Result and Optional types (or arguably just sum types if you prefer) and you're at 95%. Anything more and you're pushing into diminishing returns.
Well it depends what you're doing. 95% is like, just your opinion man. The rust type system allows, in many cases, APIs that you cannot use wrongly, or are highly resistant to incorrect usage, but to do that requires careful thinking about. To be clear, such APIs are just as relevant internally to a project as externally if you want to design a system that is long term maintainable and robust and I would argue is the point when the type system starts to get really useful (rather than diminishing returns).
This might work for the types you create, but what about all the code written in the language that expects the “proper” structure?
> Types either represent the data or not
This definitely required, but is only really the first step. Where types get really useful is when you need to change them later on. The key aspects here are how easily you can change them, and how much the language tooling can help.
you can enable word wrapping as a workaround ( `:set wrap`).
Lifehack: it can be hard to navigate in such file with just `h, j, k, l`, but you can use `gh, gj, etc`. With `g` vim will work with visual lines, while without it with just lines splitted with LF/CRLF
With a little bit of vimrc magic you can make it transparent:
"Make k/j up/down work more naturally by going to the next displayed line vs
"going to the next logical line (for when word-wrapping is on):
noremap k gk
noremap j gj
noremap <up> gk
noremap <down> gj
"Same as above, but for arrow keys in insert mode:
inoremap <up> <Esc>gka
inoremap <down> <Esc>gja
Also strikes me as not fully understanding what exactly docker is doing. In reference to building everything in a docker image:
"Unfortunately, this will rebuild everything from scratch whenever there's any change."
In this situation, with only one person as the builder, with no need for CI or CD or whatever, there's nothing wrong with building locally with all the local conveniences and just slurping the result into a docker container. Double-check any settings that may accidentally add paths if the paths have anything that would bother you. (In my case it would merely reveal that, yes, someone with my username built it and they have a "src" directory... you can tell how worried I am about both those tidbits by the fact I just posted them publicly.)
It's good for CI/CD in a professional setting to ensure that you can build a project from a hard drive, a magnetic needle, and a monkey trained to scratch a minimal kernel on to it, and boot strap from there, but personal projects don't need that.
Thank you! I got a couple minutes in and was confused as hell. There is no reason to do the builds in the container.
Even at work, I have a few projects where we had to build a Java uber jar (all the dependencies bundled into one big far) and when we need it containerized we just copy the jar in.
I honestly don't see much reason to do builds in the container unless there is some limitation in my CICD pipeline where I don't have access to necessary build tools.
It's pretty clear that this whole project was god-tier level procrastination so I wouldn't worry too much about the details. The original stated problem could have been solved with a 5-line shell script.
Half the point of containerization is to have reproducible builds. You want a build environment that you can trust will be identical 100% of the time. Your host machine is not that. If you run `pacman -Syu`, you no longer have the same build environment as you did earlier.
If you now copy your binary to the container and it implicitly expects there to be a shared library in /usr/lib or wherever, it could blow up at runtime because of a library version mismatch.
From the article, the goal was not to simplify, but rather to modernize:
> So instead, I'd like to switch to deploying my website with containers (be it Docker, Kubernetes, or otherwise), matching the vast majority of software deployed any time in the last decade.
Containers offer many benefits. To name some: process isolation, increased security, standardized logging and mature horizontal scalability.
That is what they are doing. It's a 2 stage Dockerfile.
First stage compiles the code. This is good for isolation and reproducibility.
Second stage is a lightweight container to run the compiled binary.
Why is the author being attacked (by multiple comments) for not making things simpler when that was not claimed that as the goal. They are modernizing it.
Devcontainers are a good compromise though - you can develop within a context that can be very nearly identical to production; with a bit of finagling you could even use the same dockerfile for the devcontainer, and the build image and the deployed image
Because he spends a good deal of the intro complaining that this makes his dev practice slow. So don’t do it! It has nothing to do with docker but rather the fact he is wiping the cache on every triggered build.
Meanwhile, other languages have a JIT compiler which compiles code as it runs. This would be great for development even if it turns out to be slower overall.
Actually JITs can be faster than AOT compilation because they can be optimized for the current architecture they are running in. There were claims Julia, a JIT language can beat C in some benchmarks
I don't really consider it to be slow at all. It seems about as performant as any other language this complexity, and it's far faster than the 15 minute C++ and Scala build times I'd place in the same category.
I also don’t understand this, the rust compiler hardly bothers me at all when I’m working. I feel like this is due to how bad it was early on and people just sticking to that narrative
Just like every submission about C/C++ gets a comment about how great Rust is, every submission about Rust gets a comment about how great Zig is. Like a clockwork.
Edit: apparently I am replying to the main Zig author? Language evangelism is by far the worst part of Rust and has likely stirred up more anti Rust sentiment than “converting” people to Rust. If you truly care for your language you should use whatever leverage you have to steer your community away from evangelism, not embrace it.
This comment would be a lot better if it engaged with the posted article, or really had any sort of insight beyond a single compile time metric. What do you want me to take away from your comment? Zig good and Rust bad?
As you've just demonstrated, that point can be made without even mentioning Zig, let alone copy/pasting some compile time stuff with no other comment or context. Which is why I thought (well, hoped) there might be something more to it than just a dunk attempt.
Now we get all of this off-topic discussion about Zig. Which I guess is good for you Zig folk... But it's pretty off-putting for me.
whoisyc's comment is extremely on point. As the VP of community, I would really encourage thinking about what they said.
> As you've just demonstrated, that point can be made without even mentioning Zig, let alone copy/pasting some compile time stuff with no other comment or context. Which is why I thought (well, hoped) there might be something more to it than just a dunk attempt.
Having concrete proof that something can be done more efficiently is extremely important and, no, I haven't "demonstrated" anything, since my earlier comment would have had way less substance to it without the previous context.
The comment from Andrew is not just random compiler stats, but a datapoint showing a comparable example having dramatically different performance characteristics.
You can find in this very HN submission various comments that assume that Rust's compiler performance is impossible to improve because of reasons that actually are mostly (if not entirely) irrelevant. Case in point, see people talking about how Rust compilation must take longer because of the borrow checker (and other safety checks) and Steve pointing out that, no, actually that part of the compilation pipeline is very small.
> Now we get all of this off-topic discussion about Zig.
So no, I would argue the opposite: this discussion is very much on topic.
@AndyKelley I'm super curious what you think the main factors are that make languages like Zig super fast at compiling where languages like Rust and Swift are quite slow. What's the key difference?
Basically, not depending on LLVM or LLD. The above is only possible because we invested years into making our own x86_64 backend and our own linker. You can see all the people ridiculing this decision 2 years ago https://news.ycombinator.com/item?id=36529456
LLVM isnt a good scapegoat. A C application equivalent in size to a rust or c++ application will compile an order of magnitude quicker and they all use LLVM. I'm not a compiler expert, but it doesn't seem right to me that the only possible path to quick compilation for Zig was a custom backend.
Be that as it may, many C compilers are still an order of magnitude faster than LLVM. Probably the best example is tcc, although it is not the only one. C is a much simpler language than rust, so it is expected that compilation should take less time for C. That doesn’t mean llvm isn’t a significant contributor to compilation speed. I believe cranelift compilation of rust is also much faster than the llvm path
> That doesn’t mean llvm isn’t a significant contributor to compilation speed.
That's not what I said. I said it's unlikely that fast compilation cannot be achieved while using LLVM which, I would argue, is proven by the existence of a fast compiler that uses LLVM.
It will compile an order of magnitude quicker because it often doesn't do the same thing - e.g. functions that are aggressively inlined in C++ or Rust or Zig would be compiled separately and linked normally, and generally there's less equivalent of compile-time generics in C code (because you have to either spell out all the instantiations by hand or use preprocessor or a code generator to do something that is two lines of code in C++).
I'm not Andrew, but Rust has made several language design decisions that make compiler performance difficult. Some aspects of compiler speed come down to that.
One major difference is the way each project considers compiler performance:
The Rust team has always cared to some degree about this. But, from my recollection of many RFCs, "how does this impact compiler performance" wasn't a first-class concern. And that also doesn't really speak to a lot of the features that were basically implemented before the RFC system existed. So while it's important, it's secondary to other things. And so while a bunch of hard-working people have put in a ton of work to improve performance, they also run up against these more fundamental limitations at the limit.
Andrew has pretty clearly made compiler performance a first-class concern, and that's affected language design decisions. Naturally this leads to a very performant compiler.
> Rust has made several language design decisions that make compiler performance difficult
Do you have a list off the top of your head/do you know of a decent list? I've now read many "compiler slow" thoughtpieces by many people and I have yet to see someone point at a specific feature and say "this is just intrinsically harder".
I believe that it likely exists, but would be good to know what feature to get mad at! Half joking of course
You can have your house built fast, cheap, or well. Pick two; or a bit of all three that adds up to the same effort required. You can't have all three.
You can't have a language with 100% of the possible runtime perf, 100% of the possible compile speed and 100% of the possible programmer ease-of-use.
At best you can abuse the law of diminishing returns aka the 80-20 rule, but that's not easy to balance and you run the risk of creating a language that's okay at everything, but without any strong selling points, like the stellar runtime performance Rust is known for.
So a better way to think about it is: Given Rust's numerous benefits, is having subpar compilation time really that big of a deal?
Rust heavily uses value types with specialized generics, which explodes the work needed by the compiler. It can - sometimes - improve performance. But it always slows down compilation.
I'm also curious because I've (recently) compiled more or less identical programs in Zig and Rust and they took the same amount of time to compile. I'm guessing people are just making Zig programs with less code and fewer dependencies and not really comparing apples to apples.
Zig is starting to migrate to custom backends for debug builds (instead of using LLVM) plus incremental compilation.
All Zig code is built in a single compilation unit and everything is compiled from scratch every time you change something, including all dependencies and all the parts of the stdlib that you use in your project.
So you've been comparing Zig rebuilds that do all the work every time with Rust rebuilds that cache all dependencies.
Once incremental is fully released you will see instant rebuilds.
When targeting x86_64, the self-hosted backend is already enabled by default on the latest builds of Zig (when compiling in Debug mode). The self-hosted aarch64 backend currently isn't generally usable (so we still default to LLVM when targeting aarch64), but it's likely to be the next ISA we focus on codegen for.
My non-static Rust website (includes an actual webserver as well as a react-like framework for templating) takes 1.25s to do an incremental recompile with "cargo watch" (which is an external watcher that just kills the process and reruns "cargo run").
And it can be considerably faster if you use something like subsecond[0] (which does incremental linking and hotpatches the running binary). It's not quite as fast as Zig, but it's close.
However, if that 331ms build above is a clean (uncached) build then that's a lot faster than a clean build of my website which takes ~12s.
The 331ms time is mostly uncached. In this case the build script was already cached (must be re-done if the build script is edited), and compiler_rt was already cached (must be done exactly once per target; almost never rebuilt).
What? Zig is definitively not memory-safe, while safe Rust, is, by definition, memory-safe. Unsafe rust is not memory-safe, but you generally don't need to have a lot of it around.
It’s a ten year old bug because it has never been found in the wild, ever, in those ten years. Low impact, high implementation effort bugs take less priority than bugs that affect real users.
Ferrocene is intended to document the behavior of the current version of the rustc compiler, so it's just an effort to formalize "the compiler is the language".
Yes, the soundness hole itself is low impact and doesn't need to be prioritized but it undermines the binary "Zig is definitively not memory-safe, while safe Rust, is, by definition, memory-safe" argument that was made in response to me. Now you're dealing with qualitative / quantitative questions of practical impact, in which my original statement holds: "Zig is less memory safe than Rust, but more than C/C++. Neither Zig nor Rust is fundamentally memory safe."
You can of course declare that Safe Rust is by definition memory safe, but that doesn't make it any more true than declaring that Rust solves the halting problem or that it proves P=NP. RustBelt is proven sound. Rust by contrast, as being documented by Ferrocene, is currently fundamentally unsound (though you won't hit the soundness issues in practice).
By that definition, Python is not memory-safe, Java is not memory-safe, Go is not memory-safe, and so on. All of these languages contain escape hatches to do memory-unsafe stuff, yet no one is calling them memory unsafe.
It isn't a lot of things, but I would argue that its exceptionally (heh) good exception handling model / philosophy (making it good, required, and performant) is more important than memory safety, especially when a lot of performance-oriented / bit-banging Rust code just gets shoved into Unsafe blocks anyway. Even C/C++ can be made memory safe, cf. https://github.com/pizlonator/llvm-project-deluge
What I'm more interested to know is what the runtime performance tradeoff is like now; one really has to assume that it's slower than LLVM-generated code, otherwise that monumental achievement seems to have somehow been eclipsed in very short time, with much shorter compile times to boot.
> especially when a lot of performance-oriented / bit-banging Rust code just gets shoved into Unsafe blocks anyway. Even C/C++ can be made memory safe, cf.
Your first claim is unverifiable and the second one is just so, so wrong. Even big projects with very talented, well-paid C or C++ devs eventually end up with CVEs, ~80% of them memory-related. Humans are just not capable of 0% error rate in their code.
If Zig somehow got more popular than C/C++, we would still be stuck in the same CVE bog because of memory unsafety. No thank you.
> Fil-C achieves this using a combination of concurrent garbage collection and invisible capabilities (each pointer in memory has a corresponding capability, not visible to the C address space)
With significant performance and memory overhead. That just isn't the same ballpark that Rust is playing in although hugely important if you want to bring forward performance insensitive C code into a more secure execution environment.
Fil-C has advanced a lot since I last looked at it:
> Fil-C is currently 1.5x slower than normal C in good cases, and about 4x slower in the worst cases.
with room for optimization still. Compatibility has improved massively too, due to big changes to how it works. The early versions were kind of toys, but if Filip's claims about the current version hold up then this is starting to look like a very useful bit of kit. And he has the kind of background that means we should take this seriously. There's a LOT of use cases for taking stuff written in C and eliminating memory safety issues for only a 50% slowdown.
Zig is a small and simple language. It doesn't need a complicated compiler.
Rust is a large and robust language meant for serious systems programming. The scope of problems Rust addresses is large, and Rust seeks to be deployed to very large scale software problems.
These two are not the same and do not merit an apples to apples comparison.
edit: I made some changes to my phrasing. I described Zig as a "toy" language, which wasn't the right wording.
These languages are at different stages of maturity, have different levels of complexity, and have different customers. They shouldn't be measured against each other so superficially.
This is an amusing argument to make in favor of Rust, since it's exactly the kind of dismissive statement that Ada proponents make about other languages including Rust.
(EDIT: The parent has since edited this comment to contain more than just "zig bad rust good", but I still think the combative-ness and insulting tone at the time I made this comment isn't cool.)
FWIW, I think your revised comment is far better, even though I disagree with some of the framing, there's at least some substance there.
Being frustrated by perceived bad behavior doesn't mean responding with more bad behavior is a good way to improve the discourse, if that's your goal here.
It's all good. I'm very guilty of bad behavior myself a lot of the time. It's on all of us to give gentle nudges when we see each other getting out of line. I deserve to be told the same if you see me doing this too!
Which is one of the reasons why Rust is considered to be targeting C++'s developers. C++ devs already have the Stockholm syndrome needed to tolerate the tooling.
Slow compared to what? I’m still scraping my head at this. My cargo builds are insanely fast, never taking more than a minute or two even on large projects. The only ahead of time compiled language I’ve used with faster compilation speed is Go, and that is a language specifically designed around (and arguably crippled by) the requirement for fast compilation. Rust is comparable to C compilation, and definitely faster than C++, Haskell, Java, Fortran, Algol, and Common Lisp.
How good is the debugger? "edit and continue"? Hot reload? Full IDE?
I don't know enough Rust, but I find these aspects are seriously lacking in C++ on Linux, and it is one of the few things I think Windows has it better for developers. Is Rust better?
I've only ever really used a debugger on embedded, we used gdb there. I know VS: Code has a debugger that works, I'm sure other IDEs do too.
> edit and continue
Hard to do in a pre-compiled language with no runtime, if you're asking about what I think you're asking about.
> Hot reload
Other folks gave you good links, but this stuff is pretty new, so I wouldn't claim that this is great and often good and such.
> Full IDE
I'm not aware of Rust-specific IDEs, but many IDEs have good support for Rust. VS: Code is the most popular amongst users according to the annual survey. The Rust Project distributes an official LSP server, so you can use that with any editor that supports it.
Also modern c++ with value semantics is more functional than many other languages people might come to rust from, that keeps the borrow checker from being as annoying. If people are used to making webs of stateful classes with references to each pther. The borrow checker is horrific, but that is because that design pattern is horrific if you multithread it.
Things can still be slow in absolute terms without being as slow as C++. The issues with compiling C++ are incredibly well understood and documented. It is one of the worst languages on earth for compile times. Rust doesn’t share those language level issues, so the expectations are understandably higher.
But it does share some of those issues. Specifically, while Rust generics aren't as unstructured as C++ templates, the main burden is actually from compiling all those tiny instantiations, and Rust monomorphization has the same exact problem responsible for the bulk of its compile times.
Rust shares pretty much every language-level issue C++ has with compile times, no? Monomorphization explosion, turing-complete compile time macros, complex type system.
There's a lot of overlap, but not that simple. Unless you also discount C issues that C++ inherits. Even then, there's subtleties and differences between the two that matter.
I thorougly enjoy all the work on encapsulation and reducing the steps of compilation to compile, then link that C does... Only to have C++ come along and undo almost all of it through the simple expedient of requiring templates for everything.
Oops, changed one template in one header. And that impacts.... 98% of my code.
OP could have skipped all this by doing the compilation with cache on the host system and copying the compiled statically linked binary back to the docker image build.
Incremental compilation good.
If you want, freeze the initial incremental cache after a single fresh build to use for building/deploying updates, to mitigate the risk of intermediate states gradually corrupting the cache.
Works great with docker: upon new compiler version or major website update, rebuild the layer with the incremental cache; otherwise just run from the snapshot and build newest website update version/state, and upload/deploy the resulting static binary.
Just set so that mere code changes won't force rebuilding the layer that caches/materializes the fresh clean build's incremental compilation cache.
Yeah, for application code in my experience the more I stick to the dumb way to do it the less I fight the borrow checker along with fewer trait issues.
Refactoring seems to take about the same time too so no loss on that front. After all is said and done I'm just left with various logic bugs to fix which is par for the course (at least for me) and a sense of wondering if I actually did everything properly.
I suppose maybe two years from now we'll have people that suggest avoiding generics and tempering macro usage. These days most people have heard the advice about not stressing over cloning and unwraping (though expect is much better imo) on the first pass more or less.
My 2c on this is nearly ditching rust for game development due to the compile times, in digging it turned out that LLVM is very slow regardless of opt level. Indeed it's what the Jai devs have been saying.
So Cranelift might be relevant for OP, I will shill it endlessly, took my game from 16 seconds to 4 seconds. Incredible work Cranelift team.
I participated in the most recent Bevy game jam and the community has a new tool that came out of Dioxus called subsecond which as the name suggests provides sub-second hot reloading of systems. It made prototyping very pleasant. Especially when iterating on UI.
First time someone I know in real life has made it to the HN front page (hey sharnoff, congrats) anyway -
I think this post (accidentally?) conflates two different sources of slowness:
1) Building in docker
2) The compiler being "slow"
They mention they could use bind mounts, yet wanting a clean build environment - personally, I think that may be misguided. Rust with incremental builds is actually pretty fast and the time you lose fighting dockers caching would likely be made up in build times - since you'd generally build and deploy way more often than you'd fight the cache (which, you'd delete the cache and build from scratch in that case anyway)
So - for developers who build rust containers, I highly recommend either using cache mounts or building outside the container and adding just the binary to the image.
2) The compiler being slow - having experienced ocaml, go and scala for comparisons the rust compiler is slower than go and ocaml, sure, but for non interactive (ie, REPL like) workflows, this tends not to matter in my experience - realistically, using incremental builds in dev mode takes seconds, then once the code is working, you push to CI at which point you can often accept the (worst case?) scenario that it takes 20 minutes to build your container since you're free to go do other things.
So while I appreciate the deep research and great explanations, I don't think the rust compiler is actually slow, just slower than what people might be use to coming from typescript or go for example.
A lot of people are replying to the title instead of the article.
> To get your Rust program in a container, the typical approach you might find would be something like:
If you have `cargo build --target x86_64-unknown-linux-musl` in your build process you do not need to do this anywhere in your Dockerfile. You should compile and copy into /sbin or something.
If you really want to build in a docker image I would suggest using `cargo --target-dir=/target ...` and then run with `docker run --mount type-bind,...` and then copy out of the bind mount into /bin or wherever.
The Rust compiler is slow. But if you want more features from your compiler you need to have a slower compiler, there isn't a way around that. However this blog post doesn't really seem to be around that and more an annoyance in how they deploy binaries.
>Build a new statically linked binary (with --target=x86_64-unknown-linux-musl)
>Copy it to my server
>Restart the website
Isn't it a basic C compiler feature that you can compile a file as an Object, and then link the objects into a single executable? Then you only recompile the file you changed.
I've got to say when I come across an open source project and realise it's in rust I flinch a bit know how incredibly slow the build process is. It's certainly been one of the deterrents to learning it.
What? That's absolutely ideal! It's incredibly simple. I wish deployment processes were always that simple! Docker is not going to make your deployment process simpler than that.
I did enjoy the deep dive into figuring out what was taking a long time when compiling.
The local builds are fast, why would you rebuild docker for small changes?
Also why is a personal page so much rust and so many dependencies. For a larger project with more complex stuff you’d have a test suite that takes time too. Run both in parallel in your CI and call it a day.
What "most" cases are you thinking of? Also don't forget that a binary that in release weights 10 MB, when compiled with debug symbols can weight 300 MB, which is way less practical to distribute.
WRT compilation efficiency, the C/C++ model of compiling separate translation units in parallel seems like an advance over the Rust model (but obviously forecloses opportunities for whole-program optimization).
Rust can and does compile separate translation units in parallel; it's just that the translation unit is (roughly) a crate instead of a single C or C++ source file.
rust prioritises build-time correctness: no runtime linker or no dynamic deps. all checks (types, traits, ownership) happen before execution. this makes builds sensitive to upstream changes. docker uses content-hash layers, so small context edits invalidate caches. without careful layer ordering, rust gets fully recompiled on every change.
Early design decisions favored run-time over compile-time [1]:
> * Borrowing — Rust’s defining feature. Its sophisticated pointer analysis spends compile-time to make run-time safe.
> * Monomorphization — Rust translates each generic instantiation into its own machine code, creating code bloat and increasing compile time.
> * Stack unwinding — stack unwinding after unrecoverable exceptions traverses the callstack backwards and runs cleanup code. It requires lots of compile-time book-keeping and code generation.
> * Build scripts — build scripts allow arbitrary code to be run at compile-time, and pull in their own dependencies that need to be compiled. Their unknown side-effects and unknown inputs and outputs limit assumptions tools can make about them, which e.g. limits caching opportunities.
> * Macros — macros require multiple passes to expand, expand to often surprising amounts of hidden code, and impose limitations on partial parsing. Procedural macros have negative impacts similar to build scripts.
> * LLVM backend — LLVM produces good machine code, but runs relatively slowly.
Relying too much on the LLVM optimizer — Rust is well-known for generating a large quantity of LLVM IR and letting LLVM optimize it away. This is exacerbated by duplication from monomorphization.
> * Split compiler/package manager — although it is normal for languages to have a package manager separate from the compiler, in Rust at least this results in both cargo and rustc having imperfect and redundant information about the overall compilation pipeline. As more parts of the pipeline are short-circuited for efficiency, more metadata needs to be transferred between instances of the compiler, mostly through the filesystem, which has overhead.
> * Per-compilation-unit code-generation — rustc generates machine code each time it compiles a crate, but it doesn’t need to — with most Rust projects being statically linked, the machine code isn’t needed until the final link step. There may be efficiencies to be achieved by completely separating analysis and code generation.
> * Single-threaded compiler — ideally, all CPUs are occupied for the entire compilation. This is not close to true with Rust today. And with the original compiler being single-threaded, the language is not as friendly to parallel compilation as it might be. There are efforts going into parallelizing the compiler, but it may never use all your cores.
> * Trait coherence — Rust’s traits have a property called “coherence”, which makes it impossible to define implementations that conflict with each other. Trait coherence imposes restrictions on where code is allowed to live. As such, it is difficult to decompose Rust abstractions into, small, easily-parallelizable compilation units.
> * Tests next to code — Rust encourages tests to reside in the same codebase as the code they are testing. With Rust’s compilation model, this requires compiling and linking that code twice, which is expensive, particularly for large crates.
Some code that can make Rust compilation pathologically slow is complex const expressions.
Because the compiler can evaluate a subset of expressions at compile time[1],
a complex expression can take an unbounded amount of time to evaluate.
The long-running-const-eval will by default abort the compilation if the evaluation takes too long.
On the other hand you get mentally insane if you try to work in a way that you do s.th. usefull during the 5-10 min compile times you often have with C++ projects.
When I had to deal with this I would just open the newspaper and read an article in front of my boss.
I don't think rustc is that slow. It's usually cargo/the dozens of crates that make it take a long time, even if you've set up a cache and rustc is doing nothing but hitting the cache.
Zig is faster, but then again, Zig isn't memory save, so personally I don't care. It's an impressive language, I love the syntax, the simplicity. But I don't trust myself to keep all the memory relevant invariants in my head anymore as I used to do many years ago. So Zig isn't for me. Simply not the target audience.
Why doesn't the Rust ecosystem optimize around compile time? It seems a lot of these frameworks and libraries encourage doing things which are slow to compile.
It would be more accurate to say that idiomatic Rust encourages doing things which are slow to compile: lots of small generic functions everywhere. And the most effective way to speed this up is to avoid monomorphization by using RTTI to provide a single generic compiled implementation that can be reused for different types, like what Swift does when generics across the module boundary. But this is less efficient at runtime because of all the runtime checks and computations that now need to be done to deal with objects of different sizes etc, many direct or even inlined calls now become virtual etc.
It's starting to, but a lot of people are using Rust because they need (or want) the best possible runtime performance, so that tends to be prioritised a lot of the time.
For all the C++ laughing in this thread, there's really only one thing that makes C++ slow - non-`extern` templates - and C++ gives you a lot more space to speed them up than Rust does.
As for templates, I can't think of anything about them that would speed up things substantially wrt Rust aside from extern template and manually managing your instantiations in separate .cpp files. Since otherwise it's fundamentally the same problem - recompiling the same code over and over again because it's parametrized with different types every time.
Indeed, out of the box I would actually expect C++ to do worse because a C++ header template has potentially different environment in every translation unit in which that header is included, so without precompiled headers the compiler pretty much has to assume the worst...
So there's this guy you may have heard of called Ryan Fleury who makes the RAD debugger for Epic. The whole thing is made with 278k lines of C and is built as a unity build (all the code is included into one file that is compiled as a single translation unit). On a decent windows machine it takes 1.5 seconds to do a clean compile. This seems like a clear case-study that compilation can be incredibly fast and makes me wonder why other languages like Rust and Swift can't just do something similar to achieve similar speeds.
The more your compiler does for you at build time, the longer it will take to build, it's that simple.
Go has sub-second build times even on massive code-bases. Why? because it doesn't do a lot at build time. It has a simple module system, (relatively) simple type system, and leaves a whole bunch of stuff be handled by the GC at runtime. It's great for its intended use case.
When you have things like macros, advanced type systems, and want robustness guarantees at build time.. then you have to pay for that.
I think this is mostly a myth. If you look at Rust compiler benchmarks, while typechecking isn't _free_ it's also not the bottleneck.
A big reason that amalgamation builds of C and C++ can absolutely fly is because they aren't reparsing headers and generating exactly one object file so the linker has no work to do.
Once you add static linking to the toolchain (in all of its forms) things get really fucking slow.
Codegen is also a problem. Rust tends to generate a lot more code than C or C++, so while the compiler is done doing most of its typechecking work, the backend and assembler has a lot of things to chuck through.
Not only does it generate more code, the initially generated code before optimizations is also often worse. For example, heavy use of iterators means a ton of generics being instantiated and a ton of call code for setting up and tearing down call frames. This gets heavily inlined and flattened out, so in the end it's extremely well-optimized, but it's a lot of work for the compiler. Writing it all out classically with for loops and ifs is possible, but it's harder to read.
The swift compiler is definitely bottle necked by type checking. For example, as a language requirement, generic types are left more or less in-tact after compilation. They are type checked independent of what is happening. This is unlike C++ templates which are effectively copy-pasting the resolved type with the generic for every occurrence of type resolution.
This has tradeoffs: increased ABI stability at the cost of longer compile times.
>This is unlike C++ templates which are effectively copy-pasting the resolved type with the generic for every occurrence of type resolution.
Even this can lead to unworkable compile times, to the point that code is rewritten.
A lot can be done by the programmer to mitigate slow builds in Swift. Breaking up long expressions into smaller ones and using explicit types where type inference is expensive for example.
I’d like to see tooling for this to pinpoint bottlenecks - it’s not always obvious what’s making builds slow.
>I’d like to see tooling for this to pinpoint bottlenecks - it’s not always obvious what’s making builds slow.
I second this enthusiastically.
>Codegen is also a problem. Rust tends to generate a lot more code than C or C++
Wouldn't you say a lot of that comes from the macros and (by way of monomorphisation) the type system?
That the type system is responsible for rust's slow builds is a common and enduring myth. `cargo check` (which just does typechecking) is actually usually pretty fast. Most of the build time is spent in the code generation phase. Some macros do cause problems as you mention, since the code that contains the macro must be compiled before the code that uses it, so they reduce parallelism.
> Most of the build time is spent in the code generation phase.
I can believe that, but even so it's caused by the type system monomorphising everything. When it use qsort from libc, you are using per-compiled code from a library. When you use slice::sort(), you get custom assembler compiled to suit your application. Thus, there is a lot more code generation going on, and that is caused by the tradeoffs they've made with the type system.
Rusts approach give you all sorts of advantages, like fast code and strong compile time type checking. But it comes with warts too, like fat binaries, and a bug in slice::sort() can't be fixed by just shipping of the std dynamic library, because there is no such library. It's been recompiled, just for you.
FWIW, modern C++ (like boost) that places everything in templates in .h files suffers from the same problem. If Swift suffers from it too, I'd wager it's the same cause.
It's partly by the type system. You can implement a std::sort (or slice::sort()) that just delegates to qsort or a qsort-like implementation and have roughly the same compile time performance as just using qsort straight.
But not having to is a win, as the monomorphised sorts are just much faster at runtime than having to do an indirect call for each comparison.
I just ran cargo check on nushell, and it took a minute and a half. I didn't time how long it took to compile, maybe five minutes earlier today? So I would call it faster, but still not fast.
I was all excited to conduct the "cargo check; mrustc; cc" is 100x faster experiment, but I think at best, the multiple is going to be pretty small.
Did you do it from a clean build? In that case, it's actually a slightly misleading metric, since rust needs to actually compile macros in order to typecheck code that uses them. (And therefore must also compile all the code that the macro depends on.) My bad for suggesting it, haha. Incremental cargo check is often a better way of seeing how long typechecking takes, since usually you haven't modified any macros that will need to be recompiled. On my project at work, incremental cargo check takes `1.71s`.
A ton of that is actually still doing codegen (for the proc macros for example).
Yes but I'd also add that Go specifically does not optimize well.
The compiler is optimized for compilation speed, not runtime performance. Generally speaking, it does well enough. Especially because it's usecase is often applications where "good enough" is good enough (IE, IO heavy applications).
You can see that with "gccgo". Slower to compile, faster to run.
Is gccgo really faster? Last time I looked it looked like it was abandoned (stuck at go 1.18, had no generics support) and was not really faster than the "actual" compiler.
Digging around, looks like it's workload dependent.
For pure computational workloads, it'll be faster. However, anything with heavy allocation will suffer as apparently the gccgo GC and GC related optimizations aren't as good as cgo's.
Not really. The root reason behind Go's fast compilation is that it was specifically designed to compile fast. The implementation details are just a natural consequence of that design decision.
Since fast compilation was a goal, every part of the design was looked at through a rough "can this be a horrible bottleneck?", and discarded if so. For example, the import (package) system was designed to avoid the horrible, inefficient mess of C++. It's obvious that you never want to compile the same package more than once and that you need to support parallel package compilation. These may be blindingly obvious, but if you don't think about compilation speed at design time, you'll get this wrong and will never be able to fix it.
As far as optimizations vs compile speed goes, it's just a simple case of diminishing returns. Since Rust has maximum possible perfomance as a goal, it's forced to go well into the diminishing returns territory, sacrificing a ton of compile speed for minor performance improvements. Go has far more modest performance goals, so it can get 80% of the possible performance for only 20% of the compile cost. Rust can't afford to relax its stance because it's competing with languages like C++, and to some extent C, that are willing to go to any length to squeeze out an extra 1% of perfomance.
Dlang compilers does more than any C++ compiler (metaprogramming, a better template system and compile time execution) and it's hugely faster. Language syntax design has a role here.
This is sometimes called amalgamation and you can do it Rust as well. Either manually or with tools. The point is that apart from very specific niches it is just not a practical approach.
It's not that it can't be done but that it usually is not worth the hassle and our goal should be for compilation to be fast despite not everything being in one file.
Turbo Pascal is a prime example for a compiler that won the market not least because of its - for the time - outstanding compilation speed.
In the same vein, a language can be designed for fast compilation. Pascal in general was designed for single-pass compilation which made it naturally fast. All the necessary forward declarations were a pain though and the victory of languages that are not designed for single-pass compilation proofs that while doable it was not worth it in the end.
Because Russt and Swift are doing much more work than a C compiler would? The analysis necessary for the borrow checker is not free, likewise with a lot of other compile-time checks in both languages. C can be fast because it effectively does no compile-time checking of things beyond basic syntax so you can call foo(char) with foo(int) and other unholy things.
The borrow checker is usually a blip on the overall graph of compilation time.
The overall principle is sound though: it's true that doing some work is more than doing no work. But the borrow checker and other safety checks are not the root of compile time performance in Rust.
While the borrow checker is one big difference, it's certainly not the only thing the rust compiler offers on top of C that takes more work.
Stuff like inserting bounds checking puts more work on the optimization passes and codegen backend as it simply has to deal with more instructions. And that then puts more symbols and larger sections in the input to the linker, slowing that down. Even if the frontend "proves" it's unnecessary that calculation isn't free. Many of those features are related to "safety" due to the goals of the language. I doubt the syntax itself really makes much of a difference as the parser isn't normally high on the profiled times either.
Generally it provides stricter checks that are normally punted to a linter tool in the c/c++ world - and nobody has accused clang-tidy of being fast :P
It truly is not about bounds checks. Index lookups are rare in practical Rust code, and the amount of code generated from them is miniscule.
But it _is_ about the sheer volume of stuff passed to LLVM, as you say, which comes from a couple of places, mostly related to monomorphization (generics), but also many calls to tiny inlined functions. Incidentally, this is also what makes many "modern" C++ projects slow to compile.
In my experience, similarly sized Rust and C++ projects seem to see similar compilation times. Sometimes C++ wins due to better parallelization (translation units in Rust are crates, not source files).
These languages do more at compile time, yes. However, I learned from Ryan's discord server that he did a unity build in a C++ codebase and got similar results (just a few seconds slower than the C code). Also, you could see in the article that most of the time was being spent in LLVM and linking. With a unity build, you nearly cut out link step entirely. Rust and Swift do some sophisticated things (hinley-milner, generics, etc.) but I have my doubts that those things cause the most slowdown.
That’s not a good example. Foo(int) is analyzed by compiler and a type conversion is inserted. The language spec might be bad, but this isn’t letting the compiler cut corners.
If you'd like the rust compiler to operate quickly:
* Make no nested types - these slow compiler time a lot
* Include no crates, or ones that emphasize compiler speed
C is still v. fast though. That's why I love it (and Rust).
>Make no nested types
I wouldn't like it that much
This explanation gets repeated over and over again in discussions about the speed of the Rust compiler, but apart from rare pathological cases, the majority of time in a release build is not spent doing compile-time checks, but in LLVM. Rust has zero-cost abstractions, but the zero-cost refers to runtime, sadly there's a lot of junk generated at compile-time that LLVM has to work to remove. Which is does, very well, but at cost of slower compilation.
Is it possible to generate less junk? Sounds like compiler developers took a shortcuts, which could be improved over time.
Well, zero-cost abstractions are still abstractions. It’s not junk per-se, but things that will be optimized out if the IR has enough information to safely do so, so basically lots of extra metadata to actually prove to LLVM that these things are safe.
You can address the junk problem manually by having generic functions delegate as much of their work as possible to non-generic or "less" generic functions (Where a "less" generic function is one that depends only on a known subset of type traits, such as size or alignment. Then delegating can help the compiler generate fewer redundant copies of your code, even if it can't avoid code monomorphization altogether.)
Isn't something like this blocked on the lack of specialisation?
Probably, but it's the kind of thing that needs a lot of fairly significant overhauls in the compiler architecture to really move the needle on, as far as I understand.
I encountered one project in 2000-th with few dozens of KLoC in C++. It compiled in a fraction of a second on old computer. My hello world code with Boost took few seconds to compile. So it's not just about language, it's about structuring your code and using features with heavy compilation cost. I'm pretty sure that you can write Doom with C macros and it won't be fast. I'm also pretty sure, that you can write Rust code in a way to compile very fast.
My anecdata would be that the average C++ developer puts includes inside of every header file which includes more headers to the point where everything is including everything else and a single .cpp file draws huge swaths of unnecessary code in and the project takes eons to compile on a fast computer.
That's my 2000s development experience. Fortunately I've spent a good chunk of the 2010s and most of the 2020s using other languages.
The classic XKCD compilation comic exists for a reason.
I'd be very interested to see a list of features/patterns and the cost that they incur on the compiler. Ideally, people should be able to use the whole language without having to wait so long for the result.
There is an experimental Cranelift backend[0] for rustc to improve compilation performance in debug builds.
https://github.com/rust-lang/rustc_codegen_cranelift
Templates as one single feature can be hugely variable. Its effect on compilation time can be unmeasurable. Or you can easily write a few dozen lines that will take hours to compile.
So there are few distinctive patterns I observed in that project. Please note that many of those patterns are considered anti-patterns by many people, so I don't necessarily suggest to use them.
1. Use pointers and do not include header file for class, if you need pointer to that class. I think that's a pretty established pattern in C++. So if you want to declare pointer to a class in your header, you just write `class SomeClass;` instead of `#include "SomeClass.hpp"`.
2. Do not use STL or IOstreams. That project used only libc and POSIX API. I know that author really hated STL and considered it a huge mistake to be included to the standard language.
3. Avoid generic templates unless absolutely necessary. Templates force you to write your code in header file, so it'll be parsed multiple times for every include, compiled to multiple copies, etc. And even when you use templates, try to split the class to generic and non-generic part, so some code could be moved from header to source. Generally prefer run-time polymorphism to generic compile-time polymorphism.
Why use C++ at that point? Also, pre declaring classes instead of including the corresponding headers has quite a few drawbacks.
References, for one. Also there’s a huge difference between “avoid templates unless necessary” and “don’t use templates”.
RAII? shared pointers?
I don't think it's interesting to observe that C code can be compiled quickly (so can Go, a language designed specifically for fast compilation). It's not a problem intrinsic to compilation; the interesting hard problem is to make Rust's semantics compile quickly. This is a FAQ on the Rust website.
I bet that if you take those 278k lines of code and rewrite them in simple Rust, without using generics, or macros, and using a single crate, without dependencies, you could achieve very similar compile times. The Rust compiler can be very fast if the code is simple. It's when you have dependencies and heavy abstractions (macros, generics, traits, deep dependency trees) that things become slow.
I'm curious about that point you made about dependencies. This Rust project (https://github.com/microsoft/edit) is made with essentially no dependencies, is 17,426 lines of code, and on an M4 Max it compiles in 1.83s debug and 5.40s release. The code seems pretty simple as well. Edit: Note also that this is 10k more lines than the OP's project. This certainly makes those deps suspicious.
The 'essentially no dependencies' isn't entirely true. It depends on the 'windows' crate, which is Microsoft's auto-generated Win32 bindings. The 'windows' crate is huge, and would be leading to hundreds of thousands of LoC being pulled in.
There's some other dependencies in there that are only used when building for test/benchmarking like serde, zstd, and criterion. You would need to be certain you're building only the library and not the test harness to be sure those aren't being built too.
I can't help but think the borrow checker alone would slow this down by at least 1 or 2 orders of magnitude.
Your intuition would be wrong: the borrow checker does not take much time at all.
The borrow checker is really not that expensive. On a random example, a release build of the regex crate, I see <1% of time spent in borrowck. >80% is spent in codegen and LLVM.
Again, as this been often repeated, and backed up with data, the borrow-checker is a tiny fraction of a Rust apps build time, the biggest chunk of time is spent in LLVM.
Alpha. Windows-only.
https://codeload.github.com/EpicGamesExt/raddebugger/tar.gz/...
I guess you can do that, but if for some reason you needed to compile separately, (suppose you sell the system to a third party to a client, and they need to modify module 1, module 2 and the main loop.) It would be pretty trivial to remove some #include "module3.c" lines and add some -o module3 options to the compiler. Right?
I'm not sure what Rust or docker have to do with this basic issue, it just feels like young blood attempting 2020 solutions before exploring 1970 solutions.
Every claim I've seen about unity builds being fast just never rings true to me. I just downloaded the rad debugger and ran the build script on a 7950x (about as fast as you can get). A debug build took 5s, a release build 34s with either gcc or clang.
Maybe it's a MSVC thing - it does seem to have some multi-threading stuff. In any case raddbg non-clean builds take longer than any of my rust projects.
I use unity builds day in day out. The speed up is an order of magnitude on a 2m+ LOC project.
If you want to see the difference download unreal engine and compile the editor with and without unity builds enabled.
My experience has been the polar opposite of yours - similar size rust projects are an order of magnitude slower than C++ ones. Could you share an example of a project to compare with?
That is kind of surprising. The sqlite "unity" build, has about the same number of lines of C and takes a lot longer than that to compile.
There's also Jonathan Blow's jai where he routinely builds an entire game from scratch in a few seconds (hopefully public beta will be released by the end of this year).
C hardly requires any high effort compile things. No templates, no generics, super simple types, no high level structures.
"Just". Probably because there's a lot of complexity you're waving away. Almost nothing is ever simple as "just".
At a previous company, we had a rule: whoever says "just" gets to implement it :)
I wanted to ban “just” but your rule is better. Brilliant.
That "just" was too flippant. My bad. What I meant to convey is "hey, there's some fast compiling going on here and it wasn't that hard to pull off. Can we at least take a look at why that is and maybe do the same thing?".
> "hey, there's some fast compiling going on here and it wasn't that hard to pull off. Can we at least take a look at why that is and maybe do the same thing?".
Do you really believe that nobody over the course of Rust's lifetime has ever taken a look at C compilers and thought about if techniques they use could apply to the Rust compiler?
Of course not. But it wouldn't surprise me if nobody thought to use a unity build. (Maybe they did. Idk. I'm curious).
Rust and C have differences around compilation units: Rust's already tend to be much larger than C on average, because the entire crate (aka tree of modules) is the compilation unit in Rust, as opposed to the file-based (okay not if you're on some weird architecture) compilation unit of C.
Unity builds are useful for C programs because they tend to reduce header processing overhead, whereas Rust does not have the preprocessor or header files at all.
They also can help with reducing the number of object files (down to one from many), so that the linker has less work to do, this is already sort of done (though not to literally one) due to what I mentioned above.
In general, the conventional advice is to do the exact opposite: breaking large Rust projects into more, smaller compilation units can help do less "spurious" rebuilding, so smaller changes have less overall impact.
Basically, Rust's compile time issues lie elsewhere.
Can you explain why a unity build would help? Conventional wisdom is that Rust compilation is slow in part because it has too few translation units (one per crate, plus codegen units which only sometimes work), not too many.
> makes me wonder why other languages like Rust and Swift can't just do something similar to achieve similar speeds.
One of the primary features of Rust is the extensive compile-time checking. Monomorphization is also a complex operation, which is not exclusive to Rust.
C compile times should be very fast because it's a relatively low-level language.
On the grand scale of programming languages and their compile-time complexity, C code is closer to assembly language than modern languages like Rust or Swift.
Rust is doing a lot more under the hood. C doesn't track variable lifetimes, ownership, types, generics, handle dependency management, or handle compile-time execution (beyond the limited language that is the pre-compiler). The rust compiler also makes intelligent (scary intelligent!) suggestions when you've made a mistake: it needs a lot of context to be able to do that.
The rust compiler is actually pretty fast for all the work it's doing. It's just an absolutely insane amount of additional work. You shouldn't expect it to compile as fast as C.
I’m glad that Go went the other way around: compilation speed over optimization.
For the kind of work I do — writing servers, networking, and glue code — fast compilation is absolutely paramount. At the same time, I want some type safety, but not the overly obnoxious kind that won’t let me sloppily prototype. Also, the GC helps. So I’ll gladly pay the price. Not having to deal with sigil soup is another plus point.
I guess Google’s years of experience led to the conclusion that, for software development to scale, a simple type system, GC, and wicked fast compilation speed are more important than raw runtime throughput and semantic correctness. Given the amount of networking and large - scale infrastructure software written in Go, I think they absolutely nailed it.
But of course there are places where GC can’t be tolerated or correctness matters more than development speed. But I don’t work in that arena and am quite happy with the tradeoffs that Go made.
> fast compilation is absolutely paramount. At the same time, I want some type safety, but not the overly obnoxious kind that won’t let me sloppily prototype. Also, the GC helps
Well, that point in the design space was already occupied by Java which also has extremely fast builds. Go exists primarily because the designers wanted to make a new programming language, as far as I can tell. It has some nice implementation aspects but it picked up its users mostly from the Python/Ruby/JS world rather than C/C++/Java, which was the original target market they had in mind (i.e. Google servers). Scripting language users were in the market for a language that had a type system but not one that was too advanced, and which kept the scripting "feel" of very fast turnaround times. But not Java because that was old and unhip, and all the interesting intellectual space like writing libs/conf talks was camped on already.
Java still had slow startup and warmup time circa 2005-2007, on the order of 1-3 seconds for hello world and quite a bit more for real apps. That is horrendous for anything CLI based.
And you left out classloader/classpath/JAR dependency hell, which was horrid circa late 90s/early 2000s...and I'm guessing was still a struggle when Go really started development. Especially at Google's scale.
Don't get me wrong, Java has come a long way and is a fine language and the JVM is fantastic. But the java of 2025 is not the same as mid-to-late 2000s.
You can have the best of both worlds: A fast, but sloppy compiler and slow, but thorough checkers/linters. I think it's ideal that way, but rust seems to have chosen to needlessly combine both actions into one.
That is exactly what go was meant for and there is nothing better than picking the right tool for the job. The only foot gun I have seen people run into is parallelism with mutable shared state through channels can be subtly and exploitably wrong. I don't feel like most people use channels like that though? I use rust because that isn't the job I have. I usually have to cramb slow algorithms into slower hardware, and the problems are usually almost but not quite embarrassingly parallel.
I think a lot of the materials that the Go folks put out in the early days encourage a very channel-heavy style of programming that leads to extremely bad places.
Nowadays the culture seems to have evolved a bit. I now go into high alert mode if I see a channel cross a function boundary or a goroutine that wasn't created via errgroup or similar.
People also seem to have chilled out about the "share by communicating" thing. It's usually better to just use a mutex and I think people recognise that now.
What are obnoxious types? Types either represent the data correctly or not. I think you can force types to shut up the compiler in any language including Haskell, Idris, PureScript...
I'd say you already get like 70% of the benefit of a type system with just the basic "you can't pass an int where string is expected". Being able to define your own types based on the basic ones, like "type Email string", so it's no longer possible to pass a "string" where "Email" is expected gets you to 80%. Add Result and Optional types (or arguably just sum types if you prefer) and you're at 95%. Anything more and you're pushing into diminishing returns.
Well it depends what you're doing. 95% is like, just your opinion man. The rust type system allows, in many cases, APIs that you cannot use wrongly, or are highly resistant to incorrect usage, but to do that requires careful thinking about. To be clear, such APIs are just as relevant internally to a project as externally if you want to design a system that is long term maintainable and robust and I would argue is the point when the type system starts to get really useful (rather than diminishing returns).
This might work for the types you create, but what about all the code written in the language that expects the “proper” structure?
> Types either represent the data or not
This definitely required, but is only really the first step. Where types get really useful is when you need to change them later on. The key aspects here are how easily you can change them, and how much the language tooling can help.
Is Go still in heavy use at Google these days?
What would they use for networking if not Go?
C++ and Java. Go is still used, but it's never caught up to the big two.
> Vim hangs when you open it
you can enable word wrapping as a workaround ( `:set wrap`). Lifehack: it can be hard to navigate in such file with just `h, j, k, l`, but you can use `gh, gj, etc`. With `g` vim will work with visual lines, while without it with just lines splitted with LF/CRLF
With a little bit of vimrc magic you can make it transparent:
That person seems to be confused. Installing a single, statically linked binary is clearly simpler than managing a container?!
Also strikes me as not fully understanding what exactly docker is doing. In reference to building everything in a docker image:
"Unfortunately, this will rebuild everything from scratch whenever there's any change."
In this situation, with only one person as the builder, with no need for CI or CD or whatever, there's nothing wrong with building locally with all the local conveniences and just slurping the result into a docker container. Double-check any settings that may accidentally add paths if the paths have anything that would bother you. (In my case it would merely reveal that, yes, someone with my username built it and they have a "src" directory... you can tell how worried I am about both those tidbits by the fact I just posted them publicly.)
It's good for CI/CD in a professional setting to ensure that you can build a project from a hard drive, a magnetic needle, and a monkey trained to scratch a minimal kernel on to it, and boot strap from there, but personal projects don't need that.
Thank you! I got a couple minutes in and was confused as hell. There is no reason to do the builds in the container.
Even at work, I have a few projects where we had to build a Java uber jar (all the dependencies bundled into one big far) and when we need it containerized we just copy the jar in.
I honestly don't see much reason to do builds in the container unless there is some limitation in my CICD pipeline where I don't have access to necessary build tools.
It's pretty clear that this whole project was god-tier level procrastination so I wouldn't worry too much about the details. The original stated problem could have been solved with a 5-line shell script.
Half the point of containerization is to have reproducible builds. You want a build environment that you can trust will be identical 100% of the time. Your host machine is not that. If you run `pacman -Syu`, you no longer have the same build environment as you did earlier.
If you now copy your binary to the container and it implicitly expects there to be a shared library in /usr/lib or wherever, it could blow up at runtime because of a library version mismatch.
From the article, the goal was not to simplify, but rather to modernize:
> So instead, I'd like to switch to deploying my website with containers (be it Docker, Kubernetes, or otherwise), matching the vast majority of software deployed any time in the last decade.
Containers offer many benefits. To name some: process isolation, increased security, standardized logging and mature horizontal scalability.
So put the binary in the container. Why does it have to be compiled within the container?
That is what they are doing. It's a 2 stage Dockerfile.
First stage compiles the code. This is good for isolation and reproducibility.
Second stage is a lightweight container to run the compiled binary.
Why is the author being attacked (by multiple comments) for not making things simpler when that was not claimed that as the goal. They are modernizing it.
Containers are good practice for CI/CD anyway.
I'm not sure why "complicate things unnecessarily" is considered more modern.
Don't do what you don't need to do.
You realize the author is compiling a Rust webserver for a static website right?
They are already long past the point of "complicate things unnecessarily".
A simple Dockerfile pales in comparison.
That’s a reasonable deployment strategy, but a pretty terrible local development strategy
Devcontainers are a good compromise though - you can develop within a context that can be very nearly identical to production; with a bit of finagling you could even use the same dockerfile for the devcontainer, and the build image and the deployed image
Because he spends a good deal of the intro complaining that this makes his dev practice slow. So don’t do it! It has nothing to do with docker but rather the fact he is wiping the cache on every triggered build.
Mightily resisting the urge to be flippant, but all of those benefits were achieved before Docker.
Docker is a (the, in some areas) modern way to do it, but far from the only way.
Increased security compared to bare hardware, lower than VMs. Also, lower than Jails and RKT (Rocket) which seems to be dead.
> process isolation, increased security
no, that's sandboxing.
Exactly. I immediately thought of the grug brain dev when I read that.
Meanwhile, other languages have a JIT compiler which compiles code as it runs. This would be great for development even if it turns out to be slower overall.
Actually JITs can be faster than AOT compilation because they can be optimized for the current architecture they are running in. There were claims Julia, a JIT language can beat C in some benchmarks
In fact, JITs can be faster because they can specialize code, i.e. based on the most recent data.
I don't really consider it to be slow at all. It seems about as performant as any other language this complexity, and it's far faster than the 15 minute C++ and Scala build times I'd place in the same category.
I also don’t understand this, the rust compiler hardly bothers me at all when I’m working. I feel like this is due to how bad it was early on and people just sticking to that narrative
When C++ templates are turing complete is it pointless to complain about the compile times without considering the actual code :)
My homepage takes 73ms to rebuild: 17ms to recompile the static site generator, then 56ms to run it.
Just like every submission about C/C++ gets a comment about how great Rust is, every submission about Rust gets a comment about how great Zig is. Like a clockwork.
Edit: apparently I am replying to the main Zig author? Language evangelism is by far the worst part of Rust and has likely stirred up more anti Rust sentiment than “converting” people to Rust. If you truly care for your language you should use whatever leverage you have to steer your community away from evangelism, not embrace it.
Neat, I guess?
This comment would be a lot better if it engaged with the posted article, or really had any sort of insight beyond a single compile time metric. What do you want me to take away from your comment? Zig good and Rust bad?
I think the most relevant thing is that building a simple website can (and should) take milliseconds, not minutes, and that -- quoting from the post:
> A brief note: 50 seconds is fine, actually!
50 seconds should actually not be considered fine.
As you've just demonstrated, that point can be made without even mentioning Zig, let alone copy/pasting some compile time stuff with no other comment or context. Which is why I thought (well, hoped) there might be something more to it than just a dunk attempt.
Now we get all of this off-topic discussion about Zig. Which I guess is good for you Zig folk... But it's pretty off-putting for me.
whoisyc's comment is extremely on point. As the VP of community, I would really encourage thinking about what they said.
> As you've just demonstrated, that point can be made without even mentioning Zig, let alone copy/pasting some compile time stuff with no other comment or context. Which is why I thought (well, hoped) there might be something more to it than just a dunk attempt.
Having concrete proof that something can be done more efficiently is extremely important and, no, I haven't "demonstrated" anything, since my earlier comment would have had way less substance to it without the previous context.
The comment from Andrew is not just random compiler stats, but a datapoint showing a comparable example having dramatically different performance characteristics.
You can find in this very HN submission various comments that assume that Rust's compiler performance is impossible to improve because of reasons that actually are mostly (if not entirely) irrelevant. Case in point, see people talking about how Rust compilation must take longer because of the borrow checker (and other safety checks) and Steve pointing out that, no, actually that part of the compilation pipeline is very small.
> Now we get all of this off-topic discussion about Zig.
So no, I would argue the opposite: this discussion is very much on topic.
I disagree. Zig and go are perfect frames of reference to say “actually no, Rust really is slow. Here are examples for you to go and see for yourself”
@AndyKelley I'm super curious what you think the main factors are that make languages like Zig super fast at compiling where languages like Rust and Swift are quite slow. What's the key difference?
Basically, not depending on LLVM or LLD. The above is only possible because we invested years into making our own x86_64 backend and our own linker. You can see all the people ridiculing this decision 2 years ago https://news.ycombinator.com/item?id=36529456
what is even the point of quoting reactions from two years ago?
this is a terrible look for your whole community
LLVM isnt a good scapegoat. A C application equivalent in size to a rust or c++ application will compile an order of magnitude quicker and they all use LLVM. I'm not a compiler expert, but it doesn't seem right to me that the only possible path to quick compilation for Zig was a custom backend.
Be that as it may, many C compilers are still an order of magnitude faster than LLVM. Probably the best example is tcc, although it is not the only one. C is a much simpler language than rust, so it is expected that compilation should take less time for C. That doesn’t mean llvm isn’t a significant contributor to compilation speed. I believe cranelift compilation of rust is also much faster than the llvm path
> That doesn’t mean llvm isn’t a significant contributor to compilation speed.
That's not what I said. I said it's unlikely that fast compilation cannot be achieved while using LLVM which, I would argue, is proven by the existence of a fast compiler that uses LLVM.
It will compile an order of magnitude quicker because it often doesn't do the same thing - e.g. functions that are aggressively inlined in C++ or Rust or Zig would be compiled separately and linked normally, and generally there's less equivalent of compile-time generics in C code (because you have to either spell out all the instantiations by hand or use preprocessor or a code generator to do something that is two lines of code in C++).
The Rust folks have cranelift and wild BTW. There are alternatives to LLVM and LLD, even though they might not be as obvious to most users.
I'm not Andrew, but Rust has made several language design decisions that make compiler performance difficult. Some aspects of compiler speed come down to that.
One major difference is the way each project considers compiler performance:
The Rust team has always cared to some degree about this. But, from my recollection of many RFCs, "how does this impact compiler performance" wasn't a first-class concern. And that also doesn't really speak to a lot of the features that were basically implemented before the RFC system existed. So while it's important, it's secondary to other things. And so while a bunch of hard-working people have put in a ton of work to improve performance, they also run up against these more fundamental limitations at the limit.
Andrew has pretty clearly made compiler performance a first-class concern, and that's affected language design decisions. Naturally this leads to a very performant compiler.
> Rust has made several language design decisions that make compiler performance difficult
Do you have a list off the top of your head/do you know of a decent list? I've now read many "compiler slow" thoughtpieces by many people and I have yet to see someone point at a specific feature and say "this is just intrinsically harder".
I believe that it likely exists, but would be good to know what feature to get mad at! Half joking of course
You can have your house built fast, cheap, or well. Pick two; or a bit of all three that adds up to the same effort required. You can't have all three.
You can't have a language with 100% of the possible runtime perf, 100% of the possible compile speed and 100% of the possible programmer ease-of-use.
At best you can abuse the law of diminishing returns aka the 80-20 rule, but that's not easy to balance and you run the risk of creating a language that's okay at everything, but without any strong selling points, like the stellar runtime performance Rust is known for.
So a better way to think about it is: Given Rust's numerous benefits, is having subpar compilation time really that big of a deal?
Rust heavily uses value types with specialized generics, which explodes the work needed by the compiler. It can - sometimes - improve performance. But it always slows down compilation.
I'm also curious because I've (recently) compiled more or less identical programs in Zig and Rust and they took the same amount of time to compile. I'm guessing people are just making Zig programs with less code and fewer dependencies and not really comparing apples to apples.
Zig is starting to migrate to custom backends for debug builds (instead of using LLVM) plus incremental compilation.
All Zig code is built in a single compilation unit and everything is compiled from scratch every time you change something, including all dependencies and all the parts of the stdlib that you use in your project.
So you've been comparing Zig rebuilds that do all the work every time with Rust rebuilds that cache all dependencies.
Once incremental is fully released you will see instant rebuilds.
When does this land in Zig? Will aarch64 be supported?
When targeting x86_64, the self-hosted backend is already enabled by default on the latest builds of Zig (when compiling in Debug mode). The self-hosted aarch64 backend currently isn't generally usable (so we still default to LLVM when targeting aarch64), but it's likely to be the next ISA we focus on codegen for.
I assume x86_64 is Linux only correct?
Not quite- any ELF or MachO target is enabled by default already. Windows is waiting on some COFF linker bug fixes.
Nice. Didn't realize zig build has --watch and -fincremental added. I was mostly using "watchexec -e zig zig build" for recompile on file changes.
New to 0.14.0!
My non-static Rust website (includes an actual webserver as well as a react-like framework for templating) takes 1.25s to do an incremental recompile with "cargo watch" (which is an external watcher that just kills the process and reruns "cargo run").
And it can be considerably faster if you use something like subsecond[0] (which does incremental linking and hotpatches the running binary). It's not quite as fast as Zig, but it's close.
However, if that 331ms build above is a clean (uncached) build then that's a lot faster than a clean build of my website which takes ~12s.
[0]: https://news.ycombinator.com/item?id=44369642
The 331ms time is mostly uncached. In this case the build script was already cached (must be re-done if the build script is edited), and compiler_rt was already cached (must be done exactly once per target; almost never rebuilt).
Impressive!
Zig isn’t memory safe though right?
Zig is less memory safe than Rust, but more than C/C++. Neither Zig nor Rust is fundamentally memory safe.
What? Zig is definitively not memory-safe, while safe Rust, is, by definition, memory-safe. Unsafe rust is not memory-safe, but you generally don't need to have a lot of it around.
Safe Rust is demonstrably not memory-safe: https://github.com/Speykious/cve-rs/tree/main
This is a compiler bug. This has no bearing on the language itself. Bugs happen, and they will be fixed, even this one.
It's a 10 year old bug which will eventually be fixed but may require changes to how Rust handles type variance.
Until you guys write an actual formal specification, the compiler is the language.
It’s a ten year old bug because it has never been found in the wild, ever, in those ten years. Low impact, high implementation effort bugs take less priority than bugs that affect real users.
The project is adopting Ferrocene for the spec.
Ferrocene is intended to document the behavior of the current version of the rustc compiler, so it's just an effort to formalize "the compiler is the language".
Yes, the soundness hole itself is low impact and doesn't need to be prioritized but it undermines the binary "Zig is definitively not memory-safe, while safe Rust, is, by definition, memory-safe" argument that was made in response to me. Now you're dealing with qualitative / quantitative questions of practical impact, in which my original statement holds: "Zig is less memory safe than Rust, but more than C/C++. Neither Zig nor Rust is fundamentally memory safe."
You can of course declare that Safe Rust is by definition memory safe, but that doesn't make it any more true than declaring that Rust solves the halting problem or that it proves P=NP. RustBelt is proven sound. Rust by contrast, as being documented by Ferrocene, is currently fundamentally unsound (though you won't hit the soundness issues in practice).
The second you have any `unsafe`, Rust is _by definition_ not memory-safe.
By that definition, Python is not memory-safe, Java is not memory-safe, Go is not memory-safe, and so on. All of these languages contain escape hatches to do memory-unsafe stuff, yet no one is calling them memory unsafe.
It isn't a lot of things, but I would argue that its exceptionally (heh) good exception handling model / philosophy (making it good, required, and performant) is more important than memory safety, especially when a lot of performance-oriented / bit-banging Rust code just gets shoved into Unsafe blocks anyway. Even C/C++ can be made memory safe, cf. https://github.com/pizlonator/llvm-project-deluge
What I'm more interested to know is what the runtime performance tradeoff is like now; one really has to assume that it's slower than LLVM-generated code, otherwise that monumental achievement seems to have somehow been eclipsed in very short time, with much shorter compile times to boot.
> especially when a lot of performance-oriented / bit-banging Rust code just gets shoved into Unsafe blocks anyway. Even C/C++ can be made memory safe, cf.
Your first claim is unverifiable and the second one is just so, so wrong. Even big projects with very talented, well-paid C or C++ devs eventually end up with CVEs, ~80% of them memory-related. Humans are just not capable of 0% error rate in their code.
If Zig somehow got more popular than C/C++, we would still be stuck in the same CVE bog because of memory unsafety. No thank you.
> Even C/C++ can be made memory safe, cf. https://github.com/pizlonator/llvm-project-deluge
> Fil-C achieves this using a combination of concurrent garbage collection and invisible capabilities (each pointer in memory has a corresponding capability, not visible to the C address space)
With significant performance and memory overhead. That just isn't the same ballpark that Rust is playing in although hugely important if you want to bring forward performance insensitive C code into a more secure execution environment.
Fil-C has advanced a lot since I last looked at it:
> Fil-C is currently 1.5x slower than normal C in good cases, and about 4x slower in the worst cases.
with room for optimization still. Compatibility has improved massively too, due to big changes to how it works. The early versions were kind of toys, but if Filip's claims about the current version hold up then this is starting to look like a very useful bit of kit. And he has the kind of background that means we should take this seriously. There's a LOT of use cases for taking stuff written in C and eliminating memory safety issues for only a 50% slowdown.
How confident are you that memory safety (or lack thereof) is a significant variable in how fast a compiler is?
Zig is a small and simple language. It doesn't need a complicated compiler.
Rust is a large and robust language meant for serious systems programming. The scope of problems Rust addresses is large, and Rust seeks to be deployed to very large scale software problems.
These two are not the same and do not merit an apples to apples comparison.
edit: I made some changes to my phrasing. I described Zig as a "toy" language, which wasn't the right wording.
These languages are at different stages of maturity, have different levels of complexity, and have different customers. They shouldn't be measured against each other so superficially.
This is an amusing argument to make in favor of Rust, since it's exactly the kind of dismissive statement that Ada proponents make about other languages including Rust.
Come on now. This isn't acceptable behavior.
(EDIT: The parent has since edited this comment to contain more than just "zig bad rust good", but I still think the combative-ness and insulting tone at the time I made this comment isn't cool.)
> but I still think the combative-ness and insulting tone at the time I made this comment isn't cool
Respectfully, the parent only offers up a Zig compile time metric. That's it. That's the entire comment.
This HN post about Rust is now being dominated by a cheap shot Zig one liner humblebrag from the lead author of Zig.
I think this thread needs a little more nuance.
> Respectfully, the parent only offers up a Zig compile time metric. That's it. That's the entire comment.
That's correct, but slinging cheap shots at each other is not how discussions on this site are supposed to be.
> I think this thread needs a little more nuance.
Yes, but your comment offers none.
FWIW, I think your revised comment is far better, even though I disagree with some of the framing, there's at least some substance there.
Being frustrated by perceived bad behavior doesn't mean responding with more bad behavior is a good way to improve the discourse, if that's your goal here.
You're 100% right, Steve. Thank you for your voice of moderation. You've been amazing to this community.
It's all good. I'm very guilty of bad behavior myself a lot of the time. It's on all of us to give gentle nudges when we see each other getting out of line. I deserve to be told the same if you see me doing this too!
As a former C++ developer, claims that rust compilation is slow leave me scratching my head.
Which is one of the reasons why Rust is considered to be targeting C++'s developers. C++ devs already have the Stockholm syndrome needed to tolerate the tooling.
Rust's compilation is slow, but the tooling is just about the best that any programming language has.
Slow compared to what? I’m still scraping my head at this. My cargo builds are insanely fast, never taking more than a minute or two even on large projects. The only ahead of time compiled language I’ve used with faster compilation speed is Go, and that is a language specifically designed around (and arguably crippled by) the requirement for fast compilation. Rust is comparable to C compilation, and definitely faster than C++, Haskell, Java, Fortran, Algol, and Common Lisp.
How good is the debugger? "edit and continue"? Hot reload? Full IDE?
I don't know enough Rust, but I find these aspects are seriously lacking in C++ on Linux, and it is one of the few things I think Windows has it better for developers. Is Rust better?
> How good is the debugger? "edit and continue"?
Relevant: Subsecond: A runtime hotpatching engine for Rust hot-reloading - https://news.ycombinator.com/item?id=44369642 - June, 2024 (36 comments)
> Full IDE?
https://www.jetbrains.com/rust/ (newly free for non-commercial use)
> find these aspects are seriously lacking in C++ on Linux
https://www.jetbrains.com/clion/ (same, non-commercial)
> debugger
I've only ever really used a debugger on embedded, we used gdb there. I know VS: Code has a debugger that works, I'm sure other IDEs do too.
> edit and continue
Hard to do in a pre-compiled language with no runtime, if you're asking about what I think you're asking about.
> Hot reload
Other folks gave you good links, but this stuff is pretty new, so I wouldn't claim that this is great and often good and such.
> Full IDE
I'm not aware of Rust-specific IDEs, but many IDEs have good support for Rust. VS: Code is the most popular amongst users according to the annual survey. The Rust Project distributes an official LSP server, so you can use that with any editor that supports it.
So the answer is very clear "no" on all accounts, just like for other languages built by people who don't understand the value of good tooling.
No idea because I never do that. Nor does any rust programmer I know. Which may answer your question ;)
Also modern c++ with value semantics is more functional than many other languages people might come to rust from, that keeps the borrow checker from being as annoying. If people are used to making webs of stateful classes with references to each pther. The borrow checker is horrific, but that is because that design pattern is horrific if you multithread it.
> Stockholm syndrome
A.k.a. "Remember the Vasa!" https://news.ycombinator.com/item?id=17172057
Classic case of:
New features: yes
Talking to users and fixing actual problems: lolno, I CBF
Things can still be slow in absolute terms without being as slow as C++. The issues with compiling C++ are incredibly well understood and documented. It is one of the worst languages on earth for compile times. Rust doesn’t share those language level issues, so the expectations are understandably higher.
But it does share some of those issues. Specifically, while Rust generics aren't as unstructured as C++ templates, the main burden is actually from compiling all those tiny instantiations, and Rust monomorphization has the same exact problem responsible for the bulk of its compile times.
Rust shares pretty much every language-level issue C++ has with compile times, no? Monomorphization explosion, turing-complete compile time macros, complex type system.
There's a lot of overlap, but not that simple. Unless you also discount C issues that C++ inherits. Even then, there's subtleties and differences between the two that matter.
I thorougly enjoy all the work on encapsulation and reducing the steps of compilation to compile, then link that C does... Only to have C++ come along and undo almost all of it through the simple expedient of requiring templates for everything.
Oops, changed one template in one header. And that impacts.... 98% of my code.
OP could have skipped all this by doing the compilation with cache on the host system and copying the compiled statically linked binary back to the docker image build.
Incremental compilation good. If you want, freeze the initial incremental cache after a single fresh build to use for building/deploying updates, to mitigate the risk of intermediate states gradually corrupting the cache.
Works great with docker: upon new compiler version or major website update, rebuild the layer with the incremental cache; otherwise just run from the snapshot and build newest website update version/state, and upload/deploy the resulting static binary. Just set so that mere code changes won't force rebuilding the layer that caches/materializes the fresh clean build's incremental compilation cache.
The intermediates for my project are 150GB+ alone. Last time I worked with docker images that large we had massive massive problems.
Rust compiler is very very fast but language has too many features.
The slowness is because everyone has to write code with generics and macros in Java Enterprise style in order to show they are smart with rust.
This is really sad to see but most libraries abuse codegen features really hard.
You have to write a lot of things manually if you want fast compilation in rust.
Compilation speed of code just doesn’t seem to be a priority in general with the community.
Yeah, for application code in my experience the more I stick to the dumb way to do it the less I fight the borrow checker along with fewer trait issues.
Refactoring seems to take about the same time too so no loss on that front. After all is said and done I'm just left with various logic bugs to fix which is par for the course (at least for me) and a sense of wondering if I actually did everything properly.
I suppose maybe two years from now we'll have people that suggest avoiding generics and tempering macro usage. These days most people have heard the advice about not stressing over cloning and unwraping (though expect is much better imo) on the first pass more or less.
Something something shiny tool syndrome?
Where is Cranelift mentioned
My 2c on this is nearly ditching rust for game development due to the compile times, in digging it turned out that LLVM is very slow regardless of opt level. Indeed it's what the Jai devs have been saying.
So Cranelift might be relevant for OP, I will shill it endlessly, took my game from 16 seconds to 4 seconds. Incredible work Cranelift team.
I participated in the most recent Bevy game jam and the community has a new tool that came out of Dioxus called subsecond which as the name suggests provides sub-second hot reloading of systems. It made prototyping very pleasant. Especially when iterating on UI.
https://github.com/TheBevyFlock/bevy_simple_subsecond_system
I think that’s what zig team is also doing to allow very fast build times: remove LLVM.
Yes, Zig author commented[0] that a while ago
[0] https://news.ycombinator.com/item?id=44390972
Nice, I checked a while ago and was no support for macOS aarch64, but seems that now it is supported.
Wait. You were going to ditch rust because of 16 second build times?
Over time that adds up when your coding consists of REPL like workflow.
"Wait. You were going to ditch subversion for git because of 16 second branch merge times?"
Performance matters.
Pulling out Instagram 100 times in every workday, yes, it's a total disaster
16 seconds is infuriating for something that needs to be manually tested like does this jump feel too floaty.
But it’s also probable that 16 seconds was fairly early in development and it would get much worse from there.
First time someone I know in real life has made it to the HN front page (hey sharnoff, congrats) anyway -
I think this post (accidentally?) conflates two different sources of slowness:
1) Building in docker 2) The compiler being "slow"
They mention they could use bind mounts, yet wanting a clean build environment - personally, I think that may be misguided. Rust with incremental builds is actually pretty fast and the time you lose fighting dockers caching would likely be made up in build times - since you'd generally build and deploy way more often than you'd fight the cache (which, you'd delete the cache and build from scratch in that case anyway)
So - for developers who build rust containers, I highly recommend either using cache mounts or building outside the container and adding just the binary to the image.
2) The compiler being slow - having experienced ocaml, go and scala for comparisons the rust compiler is slower than go and ocaml, sure, but for non interactive (ie, REPL like) workflows, this tends not to matter in my experience - realistically, using incremental builds in dev mode takes seconds, then once the code is working, you push to CI at which point you can often accept the (worst case?) scenario that it takes 20 minutes to build your container since you're free to go do other things.
So while I appreciate the deep research and great explanations, I don't think the rust compiler is actually slow, just slower than what people might be use to coming from typescript or go for example.
A lot of people are replying to the title instead of the article.
> To get your Rust program in a container, the typical approach you might find would be something like:
If you have `cargo build --target x86_64-unknown-linux-musl` in your build process you do not need to do this anywhere in your Dockerfile. You should compile and copy into /sbin or something.
If you really want to build in a docker image I would suggest using `cargo --target-dir=/target ...` and then run with `docker run --mount type-bind,...` and then copy out of the bind mount into /bin or wherever.
Many docker users develop on arm64-darwin and deploy to x86_64 (g)libc, so I don't think that'll work generally.
Those users are wrong :shrug:
The Rust compiler is slow. But if you want more features from your compiler you need to have a slower compiler, there isn't a way around that. However this blog post doesn't really seem to be around that and more an annoyance in how they deploy binaries.
you had a functional and minimal deployment process (compile copy restart) and now you have...
...Kubernetes.
Damn, this makes such a great ad.
>Every time I wanted to make a change, I would:
>Build a new statically linked binary (with --target=x86_64-unknown-linux-musl) >Copy it to my server >Restart the website
Isn't it a basic C compiler feature that you can compile a file as an Object, and then link the objects into a single executable? Then you only recompile the file you changed.
Not sure what I'm missing.
Just set up a build server and have your docker containers fetch prebuilt binaries from that?
I've got to say when I come across an open source project and realise it's in rust I flinch a bit know how incredibly slow the build process is. It's certainly been one of the deterrents to learning it.
> This is... not ideal.
What? That's absolutely ideal! It's incredibly simple. I wish deployment processes were always that simple! Docker is not going to make your deployment process simpler than that.
I did enjoy the deep dive into figuring out what was taking a long time when compiling.
One thing I like about Alpine Linux is how easy and dumbproof it is to make packages. It's not some wild beast like trying to create `.deb` files.
If anyone out there is already fully committed to using only Alpine Linux, I'd recommend trying creating native packages at least once.
I'm not familiar with .deb packages, but one thing I love about Arch Linux is PKGBUILD and makepkg. It is ridiculously easy to make a package.
This is such a weird cannon on sparrows approach.
The local builds are fast, why would you rebuild docker for small changes?
Also why is a personal page so much rust and so many dependencies. For a larger project with more complex stuff you’d have a test suite that takes time too. Run both in parallel in your CI and call it a day.
Unfortunately, removing debug symbols in most cases isn't a good/useful option
What "most" cases are you thinking of? Also don't forget that a binary that in release weights 10 MB, when compiled with debug symbols can weight 300 MB, which is way less practical to distribute.
WRT compilation efficiency, the C/C++ model of compiling separate translation units in parallel seems like an advance over the Rust model (but obviously forecloses opportunities for whole-program optimization).
Rust can and does compile separate translation units in parallel; it's just that the translation unit is (roughly) a crate instead of a single C or C++ source file.
And even for crates, Rust has incremental compilation.
rust prioritises build-time correctness: no runtime linker or no dynamic deps. all checks (types, traits, ownership) happen before execution. this makes builds sensitive to upstream changes. docker uses content-hash layers, so small context edits invalidate caches. without careful layer ordering, rust gets fully recompiled on every change.
Is there an equivalent of ninja for rust yet?
It depends on what you mean by 'equivalent of ninja.'
Cargo is the standard build system for Rust projects, though some users use other ones. (And some build those on top of Cargo too.)
Early design decisions favored run-time over compile-time [1]:
> * Borrowing — Rust’s defining feature. Its sophisticated pointer analysis spends compile-time to make run-time safe.
> * Monomorphization — Rust translates each generic instantiation into its own machine code, creating code bloat and increasing compile time.
> * Stack unwinding — stack unwinding after unrecoverable exceptions traverses the callstack backwards and runs cleanup code. It requires lots of compile-time book-keeping and code generation.
> * Build scripts — build scripts allow arbitrary code to be run at compile-time, and pull in their own dependencies that need to be compiled. Their unknown side-effects and unknown inputs and outputs limit assumptions tools can make about them, which e.g. limits caching opportunities.
> * Macros — macros require multiple passes to expand, expand to often surprising amounts of hidden code, and impose limitations on partial parsing. Procedural macros have negative impacts similar to build scripts.
> * LLVM backend — LLVM produces good machine code, but runs relatively slowly. Relying too much on the LLVM optimizer — Rust is well-known for generating a large quantity of LLVM IR and letting LLVM optimize it away. This is exacerbated by duplication from monomorphization.
> * Split compiler/package manager — although it is normal for languages to have a package manager separate from the compiler, in Rust at least this results in both cargo and rustc having imperfect and redundant information about the overall compilation pipeline. As more parts of the pipeline are short-circuited for efficiency, more metadata needs to be transferred between instances of the compiler, mostly through the filesystem, which has overhead.
> * Per-compilation-unit code-generation — rustc generates machine code each time it compiles a crate, but it doesn’t need to — with most Rust projects being statically linked, the machine code isn’t needed until the final link step. There may be efficiencies to be achieved by completely separating analysis and code generation.
> * Single-threaded compiler — ideally, all CPUs are occupied for the entire compilation. This is not close to true with Rust today. And with the original compiler being single-threaded, the language is not as friendly to parallel compilation as it might be. There are efforts going into parallelizing the compiler, but it may never use all your cores.
> * Trait coherence — Rust’s traits have a property called “coherence”, which makes it impossible to define implementations that conflict with each other. Trait coherence imposes restrictions on where code is allowed to live. As such, it is difficult to decompose Rust abstractions into, small, easily-parallelizable compilation units.
> * Tests next to code — Rust encourages tests to reside in the same codebase as the code they are testing. With Rust’s compilation model, this requires compiling and linking that code twice, which is expensive, particularly for large crates.
[1]: https://www.pingcap.com/blog/rust-compilation-model-calamity...
Some code that can make Rust compilation pathologically slow is complex const expressions. Because the compiler can evaluate a subset of expressions at compile time[1], a complex expression can take an unbounded amount of time to evaluate. The long-running-const-eval will by default abort the compilation if the evaluation takes too long.
1 https://doc.rust-lang.org/reference/const_eval.html
Slow compile times are a feature, get to make a cuppa.
> Slow compile times are a feature
xkcd is always relevant: https://xkcd.com/303/
On the other hand you get mentally insane if you try to work in a way that you do s.th. usefull during the 5-10 min compile times you often have with C++ projects.
When I had to deal with this I would just open the newspaper and read an article in front of my boss.
I don't think rustc is that slow. It's usually cargo/the dozens of crates that make it take a long time, even if you've set up a cache and rustc is doing nothing but hitting the cache.
It's not. It's just doing way more work than many other compilers, due to a sane type system.
Personally I don't care anymore, since I do hotpatching:
https://lib.rs/crates/subsecond
Zig is faster, but then again, Zig isn't memory save, so personally I don't care. It's an impressive language, I love the syntax, the simplicity. But I don't trust myself to keep all the memory relevant invariants in my head anymore as I used to do many years ago. So Zig isn't for me. Simply not the target audience.
Why doesn't the Rust ecosystem optimize around compile time? It seems a lot of these frameworks and libraries encourage doing things which are slow to compile.
It would be more accurate to say that idiomatic Rust encourages doing things which are slow to compile: lots of small generic functions everywhere. And the most effective way to speed this up is to avoid monomorphization by using RTTI to provide a single generic compiled implementation that can be reused for different types, like what Swift does when generics across the module boundary. But this is less efficient at runtime because of all the runtime checks and computations that now need to be done to deal with objects of different sizes etc, many direct or even inlined calls now become virtual etc.
Here's a somewhat dated but still good overview of various approaches to generics in different languages including C++, Rust, Swift, and Zig and their tradeoffs: https://thume.ca/2019/07/14/a-tour-of-metaprogramming-models...
The ecosystem is vast, and different people have different priorities. Simple as that.
It's starting to, but a lot of people are using Rust because they need (or want) the best possible runtime performance, so that tends to be prioritised a lot of the time.
TL;DR `async` considered harmful.
For all the C++ laughing in this thread, there's really only one thing that makes C++ slow - non-`extern` templates - and C++ gives you a lot more space to speed them up than Rust does.
C++ also has async these days.
As for templates, I can't think of anything about them that would speed up things substantially wrt Rust aside from extern template and manually managing your instantiations in separate .cpp files. Since otherwise it's fundamentally the same problem - recompiling the same code over and over again because it's parametrized with different types every time.
Indeed, out of the box I would actually expect C++ to do worse because a C++ header template has potentially different environment in every translation unit in which that header is included, so without precompiled headers the compiler pretty much has to assume the worst...
tldr as always, don't use Musl, if you want performance, compatibility.
tl;dr: it’s slow because it finds far more bugs before runtime than literally any other mainstream compiled language
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