Performance

go-ruby-format/format is the pure-Go library that rbgo binds for Ruby's format. This page records a comparative benchmark of that module against the reference Ruby runtimes, part of the ecosystem-wide per-module parity suite.

What is measured

The same Ruby script — sprintf with mixed conversions (%d %s %f %x %o %+d %e) in a tight loop — is run under every runtime. rbgo's number reflects this pure-Go library doing the work; every other column is that interpreter's own format stdlib. So the comparison is the Ruby-visible operation, apples-to-apples across interpreters. The script prints a deterministic checksum and its output is checked byte-identical to MRI before timing.

• Host: Apple M4 Max, macOS (darwin/arm64). Method: best-of-5 wall time (best, not mean, to suppress scheduler noise); single-shot processes, no warm-up beyond the script's own loop.
• Runtimes: ruby 4.0.5 +PRISM (MRI, the oracle) and ruby --yjit; jruby 10.1.0.0 (OpenJDK 25); truffleruby 34.0.1 (GraalVM CE Native).
• The benchmark script and harness live in rbgo's repo under bench/modules/ (format.rb + run.sh). Reproduce: RBGO=./rbgo TRUFFLE=truffleruby bash bench/modules/run.sh 5.

Result (best of 5, ms)

Runtime	time	vs MRI
rbgo (go-ruby-format)	640	1.94×
MRI (ruby 4.0.5)	330	1.00×
MRI + YJIT	310	0.94×
JRuby 10.1.0.0	1490	4.52×
TruffleRuby 34.0.1	480	1.45×

rbgo runs on go-ruby-format. The mixed-conversion sprintf loop is ~1.9x MRI / ~2.1x YJIT — within the clean-interpreter band; the per-iteration cost is dominated by interpreter dispatch around the format call, not the formatter itself.

Honest framing

JRuby and TruffleRuby are timed cold, single-shot, so they carry JVM / Graal startup on every run — read them as one-shot ruby file.rb costs, the same way rbgo and MRI are measured, not as steady-state JIT numbers. Rows that complete in well under ~200 ms carry the most relative noise; treat their ratios as order-of-magnitude. These are real measured numbers from the 2026-06-29 run — nothing is cherry-picked.