meter: add Clone method

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

meter/meter.go

@@ -28,17 +28,31 @@ var (
 
 // Meter is an interface for collecting and instrumenting metrics
 type Meter interface {
+	// Name returns meter name
 	Name() string
+	// Init initialize meter
 	Init(opts ...Option) error
+	// Clone create meter copy with new options
+	Clone(opts ...Option) Meter
+	// Counter get or create counter
 	Counter(name string, labels ...string) Counter
+	// FloatCounter get or create float counter
 	FloatCounter(name string, labels ...string) FloatCounter
+	// Gauge get or create gauge
 	Gauge(name string, fn func() float64, labels ...string) Gauge
+	// Set create new meter metrics set
 	Set(opts ...Option) Meter
+	// Histogram get or create histogram
 	Histogram(name string, labels ...string) Histogram
+	// Summary get or create summary
 	Summary(name string, labels ...string) Summary
+	// SummaryExt get or create summary with spcified quantiles and window time
 	SummaryExt(name string, window time.Duration, quantiles []float64, labels ...string) Summary
+	// Write writes metrics to io.Writer
 	Write(w io.Writer, opts ...Option) error
+	// Options returns meter options
 	Options() Options
+	// String return meter type
 	String() string
 }
 

meter/noop.go

@@ -15,6 +15,15 @@ func NewMeter(opts ...Option) Meter {
 	return &noopMeter{opts: NewOptions(opts...)}
 }
 
+// Clone return old meter with new options
+func (r *noopMeter) Clone(opts ...Option) Meter {
+	options := r.opts
+	for _, o := range opts {
+		o(&options)
+	}
+	return &noopMeter{opts: options}
+}
+
 func (r *noopMeter) Name() string {
 	return r.opts.Name
 }