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Why pure Go

go-ruby-benchmark/benchmark reimplements Ruby's standard-library Benchmark module in pure Go, with cgo disabled. The slice of Ruby it covers — formatting a Tms, its memberwise arithmetic, and the report-table layout — is deterministic and interpreter-independent: given its inputs (and the clock readings), the result is a pure function of those inputs. That is exactly the part that can — and should — live as a standalone Go library, separate from the interpreter.

The deterministic core vs. the clock

Everything Benchmark does on top of a measurement is deterministic: the Tms arithmetic, the %u %y %t %r format directives, and the bm / bmbm / benchmark table layout are pure functions of their inputs and live here. The one impure ingredient is the measurement itself — reading Process.times and Process.clock_gettime(CLOCK_MONOTONIC). That is isolated behind a small Clock interface and injected: the host wires the real process clock, and tests feed a fixed clock, so every formatted line — down to the byte — is reproducible.

Extracted from rbgo, reusable by anyone

This library began life inside go-embedded-ruby's rbgo. It has been extracted into a reusable standalone library so that:

  • any Go program can import github.com/go-ruby-benchmark/benchmark directly, with no Ruby runtime;
  • the dependency runs the other way — rbgo binds this module as a native module (the same pattern as go-ruby-regexp and go-ruby-erb), rather than this module depending on the interpreter;
  • the behavior is pinned by a differential oracle against the system ruby, fed the same fixed numbers and a deterministic clock, independent of any one consumer.

Why pure Go matters here

Because the library is CGO-free and dependency-free, it:

  • cross-compiles to every Go target with no C toolchain, and links into a single static binary;
  • has no dependency on the Ruby runtime — the dependency runs the other way;
  • can be differentially tested against the ruby binary wherever one is on PATH, while the cross-arch and Windows lanes (where ruby is absent) still validate the library itself, since the deterministic clock keeps every formatted line reproducible and ruby-free.

See Usage & API for the surface and Roadmap for what is in scope.