You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: metrics.go
    path of file: ./repos/docker-ce/components/engine/builder/dockerfile
    
    the code of the file until where you have to start completion: package dockerfile // import "github.com/docker/docker/builder/dockerfile"

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

var (
	buildsTriggered metrics.Counter
	buildsFailed    metrics.LabeledCounter
)

// Build metrics prometheus messages, these values must be initialized before
// using them. See the example below in the "builds_failed" metric definition.
cons
    
func init() {
	buildMetrics := metrics.NewNamespace("builder", "", nil)

	buildsTriggered = buildMetrics.NewCounter("builds_triggered", "Number of triggered image builds")
	buildsFailed = buildMetrics.NewLabeledCounter("builds_failed", "Number of failed image builds", "reason")
	for _, r := range []string{
		metricsDockerfileSyntaxError,
		metricsDockerfileEmptyError,
		metricsCommandNotSupportedError,
		metricsErrorProcessingCommandsError,
		metricsBuildTargetNotReachableError,
		metricsMissingOnbuildArgumentsError,
		metricsUnknownInstructionError,
		metricsBuildCanceled,
	} {
		buildsFailed.WithValues(r)
	}

	metrics.Register(buildMetrics)
}