monoruby

Ruby implementation with yet another JIT compiler written in Rust.

What's New in 2026

Monthly highlights of improvements since January 2026 (with representative PRs).

July 2026

• Big language-semantics compliance drive on the ruby/spec "language" group: destructuring, block-argument semantics, defined?, flip-flops, BEGIN/END, and predefined globals (#804–#874, notably #861).
• Implemented pattern matching (case/in, =>) (#883) and MRI's full eigenclass tower (#877).
• Green threads (M:1): scheduler core, real Thread / Mutex / Queue, scheduler-integrated blocking IO, and preemptive timeslice multithreading (#941–#944, #962).
• Real TCP / UDP / UNIX-domain sockets (#964, #981); IO::Buffer with mmap file mapping (#927, #931); IO.copy_stream (#924).
• Added the setup-monoruby GitHub Action with prebuilt binaries (#884, #886) and CRuby-compatible command-line option processing (#891).
• Completed the Exception API: raise-time backtraces, full_message, NameError / NoMethodError metadata (#893–#896).
• Brought the aarch64 JIT to optimization parity with x86-64 (#993–#1004) and shrank call frames for ~7% faster fib (#850).
• Completed Fiber — transfer / raise / kill / storage and a real root fiber, making core/fiber fully green (#1036) — and refined Thread semantics: the async Thread#raise protocol and structured Thread::Backtrace::Location (#1026, #1027).
• JIT: object allocation emitted as inline machine code (free-list pop + bump) (#1011), guard-free slot dispatch for method calls on aarch64 (#1010), and trivial-method folding through ... forwards (#1012).
• Encoding: streaming Encoding::Converter state and String#encode fallback / newline decorators (#1018, #1019); Regexp gained native-encoding byte matching for non-UTF-8 subjects plus upstream Onigmo engine fixes (#1037, #1038).
• CRuby-compatible require / load / autoload resolution rules (#1033), a Rust fnmatch engine backing Dir.glob (#1017), and an mdBook documentation site published to the project portal (#1008).

June 2026

• Completed the aarch64 JIT backend: full AsmInst coverage, inline methods, loop JIT, and recompilation on Apple Silicon (#645–#704).
• Introduced a generational GC (RGenGC-style) (#705); GC now also triggers on malloc growth (#732).
• Completed the Prism migration and removed the old hand-written parser (ruruby-parse) (#657).
• New JIT register allocation: LIR-based lowering with a per-basic-block GP register allocator; retired the R15 accumulator (#741, #756, #763).
• Cut allocation/dispatch overhead by 12–26% on addressable benchmarks (#708); zero-copy String operations (gsub, slice, lines, scan) (#722–#724).
• Made the build host-Ruby independent and reproducible (#769).

May 2026

• Switched the parser to Prism, the official Ruby parser (#412).
• Encoding subsystem overhaul: real String#encode (#443), Encoding::Converter (#447, #451), ISO-2022-JP (#449), and EUC-JP / Shift_JIS-aware string operations (#536–#545).
• Native String fast paths (reverse, rindex, case mapping, …) that beat YJIT (#493–#497); dropped per-builtin catch_unwind for +8–10% on optcarrot (#501).
• JIT: virtual FP registers with spill-to-stack (#387), heap-constant folding and Object#is_a? inlining (#504, #505), non-deopting polymorphic comparisons (#519).
• Decoupled monoruby from any host Ruby installation (#579, #595); completed the Marshal format tags (#588–#603); real File::Stat (#607); frame-local $~ / $_ (#608).
• Started the aarch64 port: VM-tier backend and macOS (Apple Silicon) support (#640, #641, #644).
• Continuous yjit-bench benchmarking against YJIT, charted on GitHub Pages (#411, #416).

April 2026

• Reimplemented Rational as a first-class Rust type with literal support (#266).
• Broad ruby/spec compliance work on Integer / Float / Array / Symbol / Class / Module (e.g. #281, #284, #309), with a live spec dashboard published on GitHub Pages (#364, #365).
• Moved shift / bitwise / ** / % into the inline-function JIT pipeline with constant folding (#307, #308), and added frame-free trivial-method optimization via ISeqHint (#290).
• Struct: per-instance slot storage with JIT-inlined member accessors (#367–#369).
• String: encoding-aware data model — code ranges, Encoding::CompatibilityError, encoding-aware char iteration (#382–#384).
• Reworked autoload as a proper state machine (#376) and added lazy heap promotion for Proc / Lambda / Binding captures (#332).

March 2026

• Implemented Marshal.dump / Marshal.load (#121, #125) and the Set class, a CRuby 4.0 built-in (#130).
• Implemented the retry statement (#109), module/class lifecycle hooks (#127), anonymous block forwarding (#128), and regex backreferences / special variables (#129).
• Added Kernel.#load (#105), correct Dir.glob (#106), Kernel.#format / sprintf (#162), and a SQLite3 FFI bridge for the sqlite3 gem (#160).
• Started a large ruby/spec compatibility push: implicit type conversions (#225), frozen-object support (#240), Errno exceptions (#250), and many crash fixes on invalid UTF-8 input (#209–#212).
• Fixed many issues to run optcarrot (#115) and the rubyboy / lee benchmarks (#111, #120).

February 2026

• Optimized rest / keyword-rest parameters in the JIT (#96).
• Corrected / and % semantics for Integer and Float (#97) and fixed Integer#digits (#99).
• Optimized the Range class (#98) and fixed Range#include? for string / beginless / endless ranges (#104).
• Introduced continuation frames (#101) and reworked JIT slot write-back logic (#102).

January 2026

• Hardened JIT frame handling so local frames are never captured by JIT-compiled code (#93).
• Added SAFETY comments to unsafe blocks across the codebase (#94).
• Introduced immediate operands (BytecodeInst::Immediate) into the bytecode (#95).

Presentation

• Presentation movie and slides for RubyKaigi2024 is here.
• Presentation movie and slides for RubyKaigi2025 is here.

Features

• Written in Rust from scratch. No dependencies on any other Ruby implementations.
• Fast. Currently, monoruby is comparable to ruby 4.0.5+YJIT/ZJIT on many benchmarks, not just optcarrot.
• Parses Ruby source with prism, the official Ruby parser (the original hand-written parser was replaced in May 2026).
• Register-based bytecode.
• Bytecode executor (virtual machine) emitting machine code directly, for both x86-64 and aarch64 (Apple Silicon).
• A compact and fast just-in-time compiler with full backends for x86-64 and aarch64. (internally using self-made dynamic assembler monoasm)

Compatibility

Conformance with Ruby has improved dramatically over the course of 2026, driven by an extensive ruby/spec-based compliance effort. As of July 2026, monoruby passes 100% of the command-line specs, 99.6% of the language specs, and about 90% of the core-library specs. Daily-updated pass statistics, compared with CRuby / TruffleRuby / JRuby, are published at rubyspec-stats.

Prerequisites

Platform

• x86-64 Linux
• aarch64 — macOS on Apple Silicon is fully supported (VM + JIT); CI runs natively on GitHub's Apple Silicon (macos-latest) runners. Linux arm64 works as well.

How to run

Please see wiki for details.

(1) Install nightly Rust.

First of all, install Rust nightly. Check here to install Rust

Caution!! only nightly Rust works for monoruby. See here to work with nightly Rust.

(2) Clone this repository.

> git clone https://github.com/sisshiki1969/monoruby.git
> cd monoruby

(3) Build and run monoruby with Ruby script file.

> cargo run --release -- test.rb

(4) or, Launch REPL.

> cargo run --bin irm

or

> bin/irm

Using monoruby in GitHub Actions

This repository doubles as a setup-monoruby action (see action.yml), modeled after ruby/setup-ruby. The ref after @ selects the monoruby version to install:

steps:
  - uses: sisshiki1969/monoruby@master # or a release tag
  - run: monoruby my_script.rb

The action first tries to download a prebuilt binary attached to a GitHub release (built by the release binaries workflow), which installs in seconds: release tags use their own release's assets, while @master / @nightly use the rolling nightly prerelease, rebuilt on every master push (so it can lag a just-pushed HEAD by one build, ~15 min). Automatic builds cover x86-64 Linux only; assets for Linux arm64 and macOS arm64 are published on demand by dispatching the release binaries workflow with the wanted tag and targets. When no asset exists for the ref/platform — or prefer-prebuilt: 'false' is set — the action falls back to building monoruby from source on the first run for each monoruby revision × runner OS/arch and caches the resulting binary and runtime tree with actions/cache, so subsequent runs restore in seconds. Linux (x64/arm64) and macOS (Apple Silicon) hosted runners are supported either way.

Inputs and outputs:

Name	Kind	Description
prefer-prebuilt ('true')	input	Set to 'false' to skip release assets and build the exact ref
cache ('true')	input	Set to 'false' to disable the source-build cache
cache-version ('v1')	input	Mixed into the cache key; bump to discard existing caches
prebuilt	output	'true' if a prebuilt release asset was used
cache-hit	output	'true' if the built binary was restored from cache
monoruby-version	output	Output of monoruby --version
ruby-version	output	RUBY_VERSION reported by the installed monoruby

Benchmark

Up-to-date benchmark results (yjit-bench, measured on every push to master) and a ruby/spec compliance dashboard are published on the project portal. The numbers below are from older one-off measurements.

1. Optcarrot banechmark

Several Ruby implementations described below were measured by optcarrot benchmark. Please see wiki for details.

Versions of used Rubies

• ruby 3.4.0dev (2024-04-27T08:56:20Z master 9ea77cb351) [x86_64-linux]
• truffleruby 24.0.1, like ruby 3.2.2, Oracle GraalVM JVM [x86_64-linux]
• truffleruby 24.0.1, like ruby 3.2.2, Oracle GraalVM Native [x86_64-linux]
• monoruby: 3e348afd4141c40978342e67ad26d42dc0b8d2a7

Optcarrot benchmark

Optcarrot fps history (0-3000 frames)

2. Other benchmarks

Several Ruby implementations described below were measured by yjit-bench. Please see wiki for details.

Versions of used Rubies

• monoruby: monoruby 0.3.0
• yjit: ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +YJIT +PRISM [x86_64-linux]
• truffleruby-24.1.1: truffleruby 24.1.1, like ruby 3.2.4, Oracle GraalVM Native [x86_64-linux]

Results

The graph shows the speed ratio against truffleruby. (higher is better)