# \[Roc\] How Our Rust-to-Zig Rewrite is Going **URL:** \ **Category:** Media\ **Created:** [July 16, 2026, 3:36pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743 "2026-07-16T15:36:45Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![alanza](https://ziggit.dev/user_avatar/ziggit.dev/alanza/32/6006_2.png) [@alanza](https://ziggit.dev/u/alanza)\ **Post date:** [July 16, 2026, 3:36pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/1 "2026-07-16T15:36:45Z")
> **[How Our Rust-to-Zig Rewrite is Going](https://rtfeldman.com/rust-to-zig)** Richard’s style of writing is less similar to mine than Andrew’s or Mitchell’s: he reads as a bit more generous and takes time to say things that I might just leave to a reader to notice. Excellent move, to move up this blog post ahead of the 0.1.0 announcement, given current events 😉 Anyway, all in all a great read. Interesting insights into the way a project’s design helps it fit into one language better or worse than another. After all this talk about tracing GCs, I’m positively itching to write a language with one in Zig and see why it’s so fiendishly difficult!! ---
**Author:** ![glfmn](https://ziggit.dev/user_avatar/ziggit.dev/glfmn/32/1763_2.png) [@glfmn](https://ziggit.dev/u/glfmn)\ **Post date:** [July 16, 2026, 8:57pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/2 "2026-07-16T20:57:28Z")
I see stuff like this and then suddenly it seems tantalizing fun: [![](https://ziggit.dev/uploads/default/original/2X/4/464c59c19f67508d30345b361107c30c47d3bb2a.jpeg "GopherCon 2025: Advancing Go Garbage Collection with Green Tea - Michael Knyszek") ](https://www.youtube.com/watch?v=gPJkM95KpKo) Granted, these tricks are sort of a like “rest of the fucking owl” situation, and I’m sure the rest of the owl bites, but optimizations like this are really cool. ---
**Author:** ![KilianHanich](https://ziggit.dev/user_avatar/ziggit.dev/kilianhanich/32/8254_2.png) [@KilianHanich](https://ziggit.dev/u/KilianHanich)\ **Post date:** [July 16, 2026, 9:26pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/3 "2026-07-16T21:26:31Z")
> As discussed earlier, having full control over allocations and deallocations is what I want in our compiler’s implementation. And in tests, I also appreciate the testing allocators detecting leaks—it can even detect leaks in compiled Roc code! Unfortunately, to get that benefit requires a lot of “init this, defer deinit” code in tests that has to be correct or else the test fails on a memory leak. None of that is necessary in Rust. I care more about the compiler’s implementation being the way I want it than the tests looking nicer, but in a perfect world I could somehow have both. For this purpose I normally just create a local arena for the test local data which I need as parameters and the like for the the actual function I want to test. ---
**Author:** ![DigitalGems9000](https://ziggit.dev/user_avatar/ziggit.dev/digitalgems9000/32/8630_2.png) [@DigitalGems9000](https://ziggit.dev/u/DigitalGems9000)\ **Post date:** [July 16, 2026, 11:18pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/4 "2026-07-16T23:18:07Z")
![rust_to_zig_rewrite](https://ziggit.dev/uploads/default/original/2X/6/64882a92c3e59029d866242747f9bcd850c6c472.jpeg) ---
**Author:** ![yosh](https://ziggit.dev/user_avatar/ziggit.dev/yosh/32/9569_2.png) [@yosh](https://ziggit.dev/u/yosh)\ **Post date:** [July 17, 2026, 11:29am UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/5 "2026-07-17T11:29:44Z")
Sounds cool - could you share an example? ---
**Author:** ![KilianHanich](https://ziggit.dev/user_avatar/ziggit.dev/kilianhanich/32/8254_2.png) [@KilianHanich](https://ziggit.dev/u/KilianHanich)\ **Post date:** [July 17, 2026, 8:12pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/6 "2026-07-17T20:12:31Z")
I don’t really have a simple example, but I guess this one works? This test isn’t supposed to check for leaks or anything else, just that it creates the correct argv for spawning a process. ```Zig test createCreateArgv { var helper_arena = std.heap.ArenaAllocator.init(std.testing.allocator); defer helper_arena.deinit(); const helper_allocator = helper_arena.allocator(); // setup const mounts = [_]container.Mount{ container.Mount{ .destination = "/test", .source = "/test", .kind = .{ .devpts = .{} }, .options = .{ .rw = true }, .propagation = .none, }, }; var env = std.process.EnvMap.init(helper_allocator); const env_key = "XDG_RUNTIME_DIR"; const env_val = "/run/hi"; try env.put(env_key, env_val); const img = b: { var img: Image = undefined; img.id = "hello"; break :b img; }; const entrypoint_argv = [_][]const u8{ "test", "test", }; const key = "key"; const name = "name"; const expected = &create_base ++ &[_][]const u8{ name, "--env", env_key ++ "=" ++ env_val, "--label", label ++ "=" ++ key, "--mount=type=devpts,destination=" ++ mounts[0].destination ++ ",ro=false,exec", img.id, } ++ entrypoint_argv; // do const args = try createCreateArgv(helper_allocator, .{ .entrypoint_argv = &entrypoint_argv, .env = env, .image = img, .mounts = &mounts, .key = key, .name = name, }); // check outer: for (expected) |e| { for (args) |a| { if (std.mem.eql(u8, e, a)) { continue :outer; } } else { const stderr = std.debug.lockStderrWriter(&.{}); defer std.debug.unlockStderrWriter(); stderr.print("missing value: {s}\nhad: {{", .{e}) catch {}; if (args.len > 0) { stderr.writeAll(args[0]) catch {}; for (args[1..]) |a| { stderr.print(", {s}", .{a}) catch {}; } } stderr.writeAll("}\n") catch {}; return error.TestValueNotFound; } } } ``` The output to stderr is to make debugging easier since the test failed, but it’s kinda hard to know which value is wrong. (This codebase is still on 0.15.2.) ---
**Author:** ![lalinsky](https://ziggit.dev/user_avatar/ziggit.dev/lalinsky/32/3720_2.png) [@lalinsky](https://ziggit.dev/u/lalinsky)\ **Post date:** [July 18, 2026, 12:38pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/7 "2026-07-18T12:38:00Z")
Was going through the Roc code and it seems that my prediction was right. Due to the `std.posix` removal, people are now resorting to this and only mainstream systems are being supported, even though this could be trivially done as POSIX/Windows split if the wrappers stayed in the library. It’s a real shame that people will have to reimplement this stuff over and over again. > ---
**Author:** ![alanza](https://ziggit.dev/user_avatar/ziggit.dev/alanza/32/6006_2.png) [@alanza](https://ziggit.dev/u/alanza)\ **Post date:** [July 18, 2026, 2:16pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/8 "2026-07-18T14:16:53Z")
i think your prediction is still too early to be called, much as you seem to want your sour grapes validated in every thread 🙂 ---
**Author:** ![yosh](https://ziggit.dev/user_avatar/ziggit.dev/yosh/32/9569_2.png) [@yosh](https://ziggit.dev/u/yosh)\ **Post date:** [July 18, 2026, 3:01pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/9 "2026-07-18T15:01:10Z")
Thanks for sharing! It seems like having to init/deinit an allocator for each test is exactly what Richard was lamenting, so I wonder if you could do that setup/teardown only once for a whole set of tests, to cut down on boilerplate? (I’m new to Zig - only just started ziglings - so forgive me if that’s a naïve question!) ---
**Author:** ![KilianHanich](https://ziggit.dev/user_avatar/ziggit.dev/kilianhanich/32/8254_2.png) [@KilianHanich](https://ziggit.dev/u/KilianHanich)\ **Post date:** [July 18, 2026, 7:15pm UTC](https://ziggit.dev/t/roc-how-our-rust-to-zig-rewrite-is-going/16743/10 "2026-07-18T19:15:43Z")
You could (by putting it into a separate function), but from my experience you rarely have much shared setup and teardown code between tests.