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

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 metrics.NewGauge in 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
Demonstrate these symbols/APIs:
  - metrics.NewGauge

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:b6ed77ca4daeebbda0a4ecec014b4e58e3491e38f7fa1f33140e89099017725d","contract":["metrics.NewGauge constructs a StandardGauge initialized to zero","metrics.NewGauge updates and retrieves arbitrary int64 values","metrics.NewGauge snapshot preserves point-in-time value isolated from subsequent updates","metrics.NewGauge snapshot panics when Update is called"],"goal":"verify metrics.NewGauge in 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,"symbols":["metrics.NewGauge"]},"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","symbols":["metrics.NewGauge"],"verifierAdapter":"golang@1"}

package sample

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

// MetricTracker manages an in-memory gauge metric.
type MetricTracker struct {
	gauge metrics.Gauge
}

// NewMetricTracker initializes a new MetricTracker with a StandardGauge.
func NewMetricTracker() *MetricTracker {
	return &MetricTracker{
		gauge: metrics.NewGauge(),
	}
}

// SetValue sets the current gauge value.
func (m *MetricTracker) SetValue(v int64) {
	m.gauge.Update(v)
}

// GetValue returns the current gauge value.
func (m *MetricTracker) GetValue() int64 {
	return m.gauge.Value()
}

// Snapshot returns a point-in-time read-only snapshot of the gauge.
func (m *MetricTracker) Snapshot() metrics.Gauge {
	return m.gauge.Snapshot()
}

// Underlying returns the underlying metrics.Gauge instance.
func (m *MetricTracker) Underlying() metrics.Gauge {
	return m.gauge
}

module example.com/sample

go 1.22.0

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=

{
  "schemaVersion": 1,
  "goal": "verify metrics.NewGauge in 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"
  ],
  "symbols": [
    "metrics.NewGauge"
  ]
}

package main

import (
	"fmt"
	"os"

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

func main() {
	// Assertion 1: metrics.NewGauge constructs a gauge initialized to 0
	g := metrics.NewGauge()
	if g == nil {
		fmt.Fprintf(os.Stderr, "FAIL: metrics.NewGauge returned nil\n")
		os.Exit(1)
	}
	if val := g.Value(); val != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: expected initial value 0, got %d\n", val)
		os.Exit(1)
	}

	// Assertion 2: Update sets gauge value and Value retrieves it
	g.Update(42)
	if val := g.Value(); val != 42 {
		fmt.Fprintf(os.Stderr, "FAIL: expected value 42 after Update, got %d\n", val)
		os.Exit(1)
	}

	g.Update(-100)
	if val := g.Value(); val != -100 {
		fmt.Fprintf(os.Stderr, "FAIL: expected value -100 after Update, got %d\n", val)
		os.Exit(1)
	}

	// Assertion 3: Snapshot captures current value and is isolated from subsequent updates
	g.Update(500)
	snap := g.Snapshot()
	if snap == nil {
		fmt.Fprintf(os.Stderr, "FAIL: Snapshot returned nil\n")
		os.Exit(1)
	}
	if snapVal := snap.Value(); snapVal != 500 {
		fmt.Fprintf(os.Stderr, "FAIL: expected snapshot value 500, got %d\n", snapVal)
		os.Exit(1)
	}

	// Update original gauge and verify snapshot remains unchanged
	g.Update(999)
	if originalVal := g.Value(); originalVal != 999 {
		fmt.Fprintf(os.Stderr, "FAIL: expected original gauge 999, got %d\n", originalVal)
		os.Exit(1)
	}
	if snapVal := snap.Value(); snapVal != 500 {
		fmt.Fprintf(os.Stderr, "FAIL: expected snapshot value to remain 500, got %d\n", snapVal)
		os.Exit(1)
	}

	// Assertion 4: Calling Update on a GaugeSnapshot panics
	panicked := false
	func() {
		defer func() {
			if r := recover(); r != nil {
				panicked = true
				if msg, ok := r.(string); !ok || msg != "Update called on a GaugeSnapshot" {
					fmt.Fprintf(os.Stderr, "FAIL: unexpected panic message: %v\n", r)
					os.Exit(1)
				}
			}
		}()
		snap.Update(1234)
	}()
	if !panicked {
		fmt.Fprintf(os.Stderr, "FAIL: expected panic when calling Update on GaugeSnapshot\n")
		os.Exit(1)
	}

	// Assertion 5: MetricTracker abstraction integrates metrics.NewGauge correctly
	tracker := sample.NewMetricTracker()
	if tracker.GetValue() != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: tracker initial value expected 0, got %d\n", tracker.GetValue())
		os.Exit(1)
	}
	tracker.SetValue(777)
	if tracker.GetValue() != 777 {
		fmt.Fprintf(os.Stderr, "FAIL: tracker value expected 777, got %d\n", tracker.GetValue())
		os.Exit(1)
	}
	tSnap := tracker.Snapshot()
	tracker.SetValue(888)
	if tSnap.Value() != 777 {
		fmt.Fprintf(os.Stderr, "FAIL: tracker snapshot expected 777, got %d\n", tSnap.Value())
		os.Exit(1)
	}

	fmt.Println("PASS: metrics.NewGauge contract passed")
}