A pure-Go implementation of Ruby — one static binary, full dynamism, zero cgo.

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go-embedded-ruby compiles Ruby to bytecode and runs it on a stack VM in the mruby/YARV lineage, with the lexer, parser and compiler embedded in the binary so eval and runtime require keep working. Ruby objects are Go heap objects, so Go's garbage collector is reused — there is no GC to write. Because it is pure Go with cgo disabled, it cross-compiles trivially and is the first Ruby you can embed inside a Go program with no C toolchain (go-mruby needs cgo).

It is not another tree-walking interpreter: dispatch goes through mutable per-class method tables (the project's objc_msgSend), so monkey-patching, define_method, method_missing, singleton classes and reflection all fall out for free. Semantics track Ruby 4.0, grown test-first against an MRI 4.0.5 and JRuby differential oracle, with systematic performance benchmarks against both and validation across all six 64-bit Go targets.

The regexp engine lives in a sibling org: go-ruby-regexp/regexp — a pure-Go reimplementation of Onigmo (Ruby's regexp engine), reusable beyond Ruby.

• Pure Go, zero cgo. Trivial cross-compilation; a static binary by default.
• Bytecode VM + embedded front-end. Ruby's dynamism — eval, runtime require, monkey-patching, method_missing — stays available at runtime.
• Reuse Go's GC. Ruby objects are Go heap objects; nothing to collect by hand.
• Build-time stdlib selection. Only the libraries the require graph reaches are embedded (build tags + //go:embed); the Go linker drops the rest.
• Ruby 4.0 semantics, test-driven growth. Conformance is verified against two independent Ruby 4.0 references — MRI (CRuby) 4.0.5 and JRuby — via a three-way differential oracle, plus a subset of ruby/spec. The bar is real-world Ruby: idioms and suites from reference applications such as Rails (ActiveSupport core_ext) and OpenVox/Puppet drive the work by demand.
• Benchmarked and portable. Performance is measured against MRI and JRuby (pure-Go CGO=0 vs C and the JVM JIT), accelerated with go-asmgen where it helps, and validated on all six 64-bit architectures (amd64, arm64, riscv64, loong64, ppc64le, s390x).
• 100% test coverage is the target, enforced as a CI gate.

Phases 0–7 — done (core); Phase 8 (conformance & performance) active. The object model and essentially all of idiomatic Ruby run today, every feature differential-tested against MRI Ruby 4.0.5 (and JRuby) with 100% coverage enforced in CI across all six 64-bit arches:

• Values: integers, floats, strings, symbols, arrays, ordered hashes, ranges (incl. beginless/endless), Proc/lambda, Regexp/MatchData, Struct.
• Methods & blocks: the full argument system (required/optional/*splat/ keyword/**rest/&block), { }/do…end blocks, yield, block_given?, Proc/lambda/stabby ->(){}, &proc block-pass, Symbol#to_proc, setter defs def name=, endless methods def foo = expr, super.
• Classes & modules: inheritance, @ivars, new/initialize, constants and constant assignment, class methods def self.foo, include mixins, attr_accessor/reader/writer, Struct.new.
• Metaprogramming: method_missing, send/public_send, respond_to?, define_method, instance_eval/instance_exec, class_eval/module_eval/class_exec, instance_variable_get/set/defined?.
• Control flow: if/unless/while/until + modifiers, case/when, begin/rescue/ensure/else/retry, break/next.
• Collections: Array/Hash/Range with Enumerable and Comparable, both written once in embedded Ruby.
• Strings: interpolation, %/format/sprintf, and a broad method set.
• Regular expressions: /re/imx literals, Regexp/MatchData, =~/match/scan/gsub/sub/split and the match globals, on the pure-Go go-ruby-regexp/regexp engine (build stays CGO=0).

Mutable String, pattern matching case/in, Fiber, Thread and arbitrary-precision Bignum have all landed; rbgo also binds 181 pure-Go go-ruby-* modules as native require-able libraries — from the stdlib through databases (mysql2, mongo, etcd, bolt), messaging (nats, kafka), RPC / data (grpc, google/protobuf, arrow, parquet), web / security (faraday, puma, graphql, saml, webauthn, acme, rbnacl, age) and docs / observability (prawn, bleve, opentelemetry). (In the js/wasm build the socket/OS-bound backends among these are compiled out — require raises LoadError.) Still ahead is Phase 8 (conformance & performance); the roadmap has the detail.

BSD-3-Clause.