github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:9254298e8182305dd05b987fdea712ebcd17e624094088da047e278c80f6e4ca","contract":["metrics.NewGauge constructs an int64 gauge with initial value 0","Gauge.Update updates the stored int64 value","Gauge.Value retrieves the current stored int64 value","Gauge.Snapshot captures an immutable point-in-time snapshot of the gauge","metrics.NewGaugeFloat64 constructs a float64 gauge with initial value 0.0","GaugeFloat64.Update and Value store and retrieve float64 values","metrics.NewFunctionalGauge evaluates a callback function to return dynamic values","metrics.GetOrRegisterGauge registers a new gauge or returns an existing one from a registry"],"goal":"verify pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9","kind":"HOW","packages":["pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9"],"schemaVersion":1},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9"],"schemaVersion":1,"subject":"pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9","verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9

github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9 h1:bsUq1dX0N8AOIL7EB/X911+m4EHsnWEHeJ0c+3TTBrg=
github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=

package main

import (
	"fmt"

	"github.com/rcrowley/go-metrics"
)

func main() {
	// Create a new metrics registry
	registry := metrics.NewRegistry()

	// Create and register a standard int64 gauge
	gauge := metrics.NewGauge()
	if err := registry.Register("queue.size", gauge); err != nil {
		panic(err)
	}
	gauge.Update(42)

	// Create and register a float64 gauge
	gaugeFloat := metrics.NewGaugeFloat64()
	if err := registry.Register("cpu.load", gaugeFloat); err != nil {
		panic(err)
	}
	gaugeFloat.Update(0.75)

	// Register or get an existing gauge
	cachedGauge := metrics.GetOrRegisterGauge("memory.used_mb", registry)
	cachedGauge.Update(1024)

	// Retrieve and print gauge values
	g := registry.Get("queue.size").(metrics.Gauge)
	gf := registry.Get("cpu.load").(metrics.GaugeFloat64)
	gm := registry.Get("memory.used_mb").(metrics.Gauge)

	fmt.Printf("queue.size: %d\n", g.Value())
	fmt.Printf("cpu.load: %.2f\n", gf.Value())
	fmt.Printf("memory.used_mb: %d\n", gm.Value())
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20250401214520-65e299d6c5c9"
  ]
}

package main

import (
	"fmt"
	"math"
	"os"

	"github.com/rcrowley/go-metrics"
)

func main() {
	// 1. metrics.NewGauge constructs an int64 gauge with initial value 0
	g := metrics.NewGauge()
	if g == nil {
		fmt.Fprintf(os.Stderr, "metrics.NewGauge returned nil\n")
		os.Exit(1)
	}
	if g.Value() != 0 {
		fmt.Fprintf(os.Stderr, "expected initial gauge value 0, got %d\n", g.Value())
		os.Exit(1)
	}

	// 2. Gauge.Update updates the stored int64 value
	g.Update(42)
	if g.Value() != 42 {
		fmt.Fprintf(os.Stderr, "expected gauge value 42, got %d\n", g.Value())
		os.Exit(1)
	}
	g.Update(-100)
	if g.Value() != -100 {
		fmt.Fprintf(os.Stderr, "expected gauge value -100, got %d\n", g.Value())
		os.Exit(1)
	}

	// 3. Gauge.Value retrieves the current stored int64 value
	g.Update(999999)
	if val := g.Value(); val != 999999 {
		fmt.Fprintf(os.Stderr, "expected gauge value 999999, got %d\n", val)
		os.Exit(1)
	}

	// 4. Gauge.Snapshot captures an immutable point-in-time snapshot of the gauge
	g.Update(500)
	snap := g.Snapshot()
	if snap == nil || snap.Value() != 500 {
		fmt.Fprintf(os.Stderr, "expected snapshot value 500, got %v\n", snap)
		os.Exit(1)
	}
	g.Update(1000)
	if snap.Value() != 500 {
		fmt.Fprintf(os.Stderr, "expected snapshot value to remain 500 after gauge update, got %d\n", snap.Value())
		os.Exit(1)
	}
	panicked := false
	func() {
		defer func() {
			if recover() != nil {
				panicked = true
			}
		}()
		snap.Update(2000)
	}()
	if !panicked {
		fmt.Fprintf(os.Stderr, "expected snap.Update to panic on snapshot\n")
		os.Exit(1)
	}

	// 5. metrics.NewGaugeFloat64 constructs a float64 gauge with initial value 0.0
	gf := metrics.NewGaugeFloat64()
	if gf == nil {
		fmt.Fprintf(os.Stderr, "metrics.NewGaugeFloat64 returned nil\n")
		os.Exit(1)
	}
	if gf.Value() != 0.0 {
		fmt.Fprintf(os.Stderr, "expected initial float64 gauge value 0.0, got %f\n", gf.Value())
		os.Exit(1)
	}

	// 6. GaugeFloat64.Update and Value store and retrieve float64 values
	gf.Update(3.14159)
	if math.Abs(gf.Value()-3.14159) > 1e-9 {
		fmt.Fprintf(os.Stderr, "expected float64 gauge value 3.14159, got %f\n", gf.Value())
		os.Exit(1)
	}
	gfSnap := gf.Snapshot()
	if math.Abs(gfSnap.Value()-3.14159) > 1e-9 {
		fmt.Fprintf(os.Stderr, "expected float64 snapshot value 3.14159, got %f\n", gfSnap.Value())
		os.Exit(1)
	}
	gf.Update(2.71828)
	if math.Abs(gfSnap.Value()-3.14159) > 1e-9 {
		fmt.Fprintf(os.Stderr, "expected float64 snapshot to remain unchanged, got %f\n", gfSnap.Value())
		os.Exit(1)
	}
	gfPanicked := false
	func() {
		defer func() {
			if recover() != nil {
				gfPanicked = true
			}
		}()
		gfSnap.Update(1.0)
	}()
	if !gfPanicked {
		fmt.Fprintf(os.Stderr, "expected gfSnap.Update to panic on snapshot\n")
		os.Exit(1)
	}

	// 7. metrics.NewFunctionalGauge evaluates a callback function to return dynamic values
	dynamicCount := int64(10)
	fg := metrics.NewFunctionalGauge(func() int64 {
		return dynamicCount * 2
	})
	if fg == nil || fg.Value() != 20 {
		fmt.Fprintf(os.Stderr, "expected functional gauge value 20, got %v\n", fg)
		os.Exit(1)
	}
	dynamicCount = 25
	if fg.Value() != 50 {
		fmt.Fprintf(os.Stderr, "expected updated functional gauge value 50, got %d\n", fg.Value())
		os.Exit(1)
	}

	// 8. metrics.GetOrRegisterGauge registers a new gauge or returns an existing one from a registry
	reg := metrics.NewRegistry()
	rg1 := metrics.GetOrRegisterGauge("app.worker_count", reg)
	if rg1 == nil {
		fmt.Fprintf(os.Stderr, "GetOrRegisterGauge returned nil\n")
		os.Exit(1)
	}
	rg1.Update(8)

	rg2 := metrics.GetOrRegisterGauge("app.worker_count", reg)
	if rg2.Value() != 8 {
		fmt.Fprintf(os.Stderr, "expected existing registered gauge value 8, got %d\n", rg2.Value())
		os.Exit(1)
	}
	rg2.Update(16)
	if rg1.Value() != 16 {
		fmt.Fprintf(os.Stderr, "expected both references to reflect updated value 16, got %d\n", rg1.Value())
		os.Exit(1)
	}

	fmt.Println("All go-metrics contract assertions passed.")
}