zoptia0regex

⚡ Faster than Go. Identical to Go. Provably.

Head-to-head against Go’s standard-library regexp — same patterns, same inputs, same 256 KB corpus, same calibration, Zig built ReleaseFast — zoptia0regex is ~11% faster on average and compiles patterns ~1.7× faster. And it doesn’t trade correctness for speed: ~30,000 differential tests prove its output is byte-for-byte identical to Go’s.

Not “inspired by.” Proven identical.

• 🚀 Faster than Go at matching. Geometric mean across 20 workloads: 0.887× Go’s time. Anchored “validation” patterns hit the one-pass engine and fly — up to ~1.7× faster.
• 🛡️ Linear-time. ReDoS-proof. Thompson NFA simulation means no catastrophic backtracking, ever. A pattern like (a+)+ that hangs PCRE, JS, and Python runs in linear time here.
• ✅ Proven identical to Go. ~30,000 differential cases run the real Go regexp and this engine on the same inputs and require identical results. Zero mismatches. Zero leaks. The fidelity isn’t a claim — it’s enforced by the suite on every push.
• 🌍 Unicode-correct. (?i) case folding uses tables generated directly from Go’s unicode.SimpleFold — correct across all of Unicode, not just ASCII.

In a nutshell

var re = try regex.compile(gpa, "(\\w+)@(\\w+)\\.(\\w+)");
defer re.deinit();

const subs = (try re.findSubmatch(gpa, "ping me@example.com")).?;
// subs => "me" / "example" / "com"

→ Full install & API in the usage guide.

📊 The benchmark

Zig vs Go, same workload, same machine. Lower is faster — < 1.0× means Zig wins.

The honest caveat: there is exactly one workload where Go wins — an unanchored case-insensitive scan ((?i)performance over 256 KB) at 1.29×. That’s a Pike-VM constant factor, not a missing engine (one-pass requires anchoring). Everything else is on par or faster. Full methodology and the complete table: BENCHMARKS.md.

Why this exists

zoptia0regex is a faithful, high-fidelity replica of Go’s standard-library regexp package — the RE2 design by Russ Cox. It mirrors Go’s leftmost-first match semantics (plus POSIX leftmost-longest), the same Find / Replace / Split / submatch API surface, and the same four-stage pipeline: parse → simplify → compile → execute. All three of Go’s execution engines are here — the one-pass matcher, the bitstate backtracker, and the Pike VM — plus literal-prefix acceleration, with the engine chosen automatically per pattern.

That’s where the speed and the fidelity come from. For the full design walkthrough, see docs/internals.md.

Features

• 🧩 Full Go regexp/syntax: literals, alternation, character classes ([...], [^...], ranges, Perl \d\w\s, POSIX [[:alpha:]], Unicode \p{...} curated subset), ., anchors ^ $ \A \z \b \B.
• 🔁 Quantifiers * + ? {n,m}, greedy and non-greedy.
• 🏷️ Capturing, non-capturing, and named groups; inline flags (?imsU); escapes; \Q...\E.
• ⚖️ Two match modes: leftmost-first (Go default) and POSIX leftmost-longest.
• 🛡️ Linear-time guarantee — immune to ReDoS.
• ⚡ Allocation-free hot loops: reuse a Scratch across matches (matchScratch) for zero-allocation steady state, like Go’s machine pool.
• 🌍 Full-Unicode case folding via Go-derived tables.
• 🚫 Same intentional limits as RE2/Go: no backreferences, no \C.

Install & use

Requires Zig 0.16.

zig fetch --save git+https://github.com/zoptia/zoptia0regex

const regex = @import("regex");

var re = try regex.compile(gpa, "(\\w+)@(\\w+)\\.(\\w+)");
defer re.deinit();
const subs = (try re.findSubmatch(gpa, "ping me@example.com")).?;

That’s the taste — the full install + API guide lives in docs/usage.md: wiring the dependency into build.zig, every Find / FindAll / Replace / Split / submatch variant, the memory model, and POSIX mode.

Trust & validation

Every push runs the full ~30,000-case differential suite in CI, across three corpora:

Each case runs the real Go regexp and zoptia0regex on the same input and requires byte-for-byte identical FindSubmatchIndex / FindAll / ReplaceAll / Split. Result: zero mismatches, zero memory leaks (checked under std.testing.allocator). CI stays green.

zig build test        # unit + behaviour tests
zig build difftest    # the full ~30k differential suite (no Go toolchain needed)
zig build bench       # benchmark vs Go (ReleaseFast)

License & acknowledgement

Licensed under Apache-2.0.

zoptia0regex is a faithful port of Go’s standard-library regexp package. Deep thanks to Russ Cox and the Go authors — portions are derived from Go’s BSD-3-Clause-licensed code, attributed in NOTICE. Not affiliated with Go or Google.