The 15-Minute Systems Crash Course

You already ship systems code. Here is the whole model, densely.

Memory: deterministic reclamation

ARC by default. The compiler inserts atomic retains/releases; non-escaping arguments pass as borrows with no traffic. Cyclic edges use GenRef<T> generational handles (.get() yields null after the owner frees). Intentional strong cycles opt out per field with #[Allow(CyclicReference)] plus manual clearing. Destructors synthesize recursively; locals drop at scope end. Raw pointers and C-ABI calls live in unsafe {} only.

Builds: two engines

Dev loop runs the Cranelift JIT: a cold dev build lands in 35-60 ms on the current baseline (benches/data/benchmarks.json, 2026-09-29), a hot-reload swap turns around in about 7 ms, and rnx check answers with no codegen at all. Release runs LLVM -O3 over per-function sections, then links with section garbage collection into a stripped ~356 KB binary. Both modes are measured on the proving-ground chart, as rnx run and rnx build sim.rnx --release:

rnx run sim.rnx          # interpreter / JIT dev loop
rnx build sim.rnx --release  # LLVM -O3 AOT binary

SIMD: lanes, not intrinsics

Vec4f is a 128-bit value type with no heap allocation and no ARC traffic. Construct it, combine it with plain operators, read lanes back out. Vectors cross function boundaries as params and returns on all three backends:

import { Vec4f } from "@std/simd";

fn dbl(v: Vec4f): Vec4f {
    return v * Vec4f.splat(2.0);
}

print(dbl(new Vec4f(1.0, 2.0, 3.0, 4.0)).get(2));

C-ABI: headers in, symbols out

rnx build --lib compiles top-level export fn items to C-ABI wrappers in a static archive plus a <basename>.h header. No binding generator, no wrapper crate, no build script:

rnx build physics.rnx --lib -o libphysics.a

Integers, floats, bools, and String (as const char*) cross the boundary. Anything else in a pub signature fails with E108.

Diagnostics and tooling

One binary: check, run, build, test (per-test timings, tree-hook failure boxes), bench, lint --fix, fmt, doc --json, lsp, explain <code>. Errors render as tree-hook codeframes with ▲ pointers and got:/expected: lines.

Done. Fifteen minutes. Go build.