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- Hacker News
- > Futures aren't (trivially) inlined
In my programming language I wrote custom pass for inlining async function calls within other async functions. It generally works and allows to remove some boilerplate, but it increases result binary size a lot.
Technically Rust can do the same.
by Panzerschrek - I recently started working with Rust async. The main issue I am currently facing is code duplication: I have to duplicate every function that I want to support both asynchronous and blocking APIs. This could be great to have a `maybe-async`. I took a look at the available crates to work around this (maybe-async, bisync), but they all have issues or hard limitations.by conaclos
- I like this article already because it took me to the goals of Rust for 2026. We use the language in our team, but we haven't needed to go very deep to do the stuff we need. Yet, I really enjoy witnessing the development of a language from ground up with so much community feedback.
I somehow miss noticing that in C++ and I have no idea how it is working in other domains.
My only gripe is that a lot of it is feeling a bit kick-starter-y, with each of the goals needing specific funding. Is that the best model we've found so far?
- This is the type of ugly but necessary discussions that have been happening in c++ for a while.
I never really liked the viral nature of async in rust when it was introduced.
I wish rust the best of luck and with more people like this rust could have a brighter future.
by hacker_homie - I don’t understand why Rust even has panics if its primary goal is safety. We should be able to prove that the code has no paths that may panic ever. I’ve been looking at this all week. It’s very difficult to make a program that is guaranteed not to panic. My understanding is that the panic handler is about 300kb, and the only way to exclude it is if your code has no paths that can panic when it compiles. And after it compiles you can check the binary to see if the panic handler was included. It’s hacky.
Yes you can lint out unwraps and other panic operations, but if there was a subset of no-panic rust a large part of the issue detailed in this post goes away. But it’s frustrating working with a language that has so many operations that can, in theory, panic even if in practice they should only do so if a bit flips. Like a proving an array is non-empty or working with async. You either end up with a lot of error handling for situations which will never happen or really strange patterns like non-empty list pattern (structure with first field and then your list). Which of course ends up adding its own bloat.
by J_Shelby_J - Async seems like an underbaked idea across the board. Regular code was already async. When you need to wait for an async operation, the thread sleeps until ready and the kernel abstracts it away. But We didn’t like structuring code into logical threads, so we added callback systems for events. Then realized callbacks are very hard to reason about and that sequential control is better.
So threads was the right programming model.
Now language runtimes prefer “green threads” for portability and performance but most languages don’t provide that properly. Instead we have awkward coloring of async/non-async and all these problems around scheduling, priority, and no-preemption. It’s a worse scheduling and process model than 1970.
- Great article! Love these types of deep dives into optimizations. Hope the project goal works out!
I've felt before that compilers often don't put much effort into optimizing the "trivial" cases.
Overly dramatic title for the content, though. I would have clicked "Async Rust Optimizations the Compiler Still Misses" too you know
by hmry - Agree with the other commenters that the title is a bit too dramatic. The content was well written and got the point across.
I still don’t have enough experience to have a strong opinion on Rust async, but some things did standout.
On the good side, it’s nice being able to have explicit runtimes. Instead of polluting the whole project to be async, you can do the opposite. Be sync first and use the runtime on IO “edges”. This was a great fit to a project that I’m working on and it seems like a pretty similar strategy to what zig is doing with IO code. This largely solved the function colloring problem in this particular case. Strict separation of IO and CPU bound code was a requirement regardless of the async stuff, so using the explicit IO runtime was natural.
On the bad side, it seems crazy to me how much the whole ecosystem depends on tokio. It’s almost like Java’s GC was optional, but in practice everyone just used the same third party GC runtime and pulling any library forced you to just use that runtime. This sort of central dependency is simply not healthy.