don't re-instantiate nop instruments everywhere (#610)

Author: lucix-aws

.changelog/ae0ef34a003c42149a078ca1288c1360.json

@@ -1,8 +1,8 @@
 {
     "id": "ae0ef34a-003c-4214-9a07-8ca1288c1360",
     "type": "bugfix",
-    "description": "Avoid unnecessary allocation overhead from httptrace.WithClientTrace when the client isn't using a metrics sink.",
+    "description": "Avoid unnecessary allocation overhead from the metrics system when not in use.",
     "modules": [
         "."
     ]
-}
+}

metrics/nop.go

@@ -19,72 +19,72 @@ var _ Meter = (*NopMeter)(nil)
 
 // Int64Counter creates a no-op instrument.
 func (NopMeter) Int64Counter(string, ...InstrumentOption) (Int64Counter, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Int64UpDownCounter creates a no-op instrument.
 func (NopMeter) Int64UpDownCounter(string, ...InstrumentOption) (Int64UpDownCounter, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Int64Gauge creates a no-op instrument.
 func (NopMeter) Int64Gauge(string, ...InstrumentOption) (Int64Gauge, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Int64Histogram creates a no-op instrument.
 func (NopMeter) Int64Histogram(string, ...InstrumentOption) (Int64Histogram, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Int64AsyncCounter creates a no-op instrument.
 func (NopMeter) Int64AsyncCounter(string, Int64Callback, ...InstrumentOption) (AsyncInstrument, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Int64AsyncUpDownCounter creates a no-op instrument.
 func (NopMeter) Int64AsyncUpDownCounter(string, Int64Callback, ...InstrumentOption) (AsyncInstrument, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Int64AsyncGauge creates a no-op instrument.
 func (NopMeter) Int64AsyncGauge(string, Int64Callback, ...InstrumentOption) (AsyncInstrument, error) {
-	return nopInstrument[int64]{}, nil
+	return nopInstrumentInt64, nil
 }
 
 // Float64Counter creates a no-op instrument.
 func (NopMeter) Float64Counter(string, ...InstrumentOption) (Float64Counter, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 // Float64UpDownCounter creates a no-op instrument.
 func (NopMeter) Float64UpDownCounter(string, ...InstrumentOption) (Float64UpDownCounter, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 // Float64Gauge creates a no-op instrument.
 func (NopMeter) Float64Gauge(string, ...InstrumentOption) (Float64Gauge, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 // Float64Histogram creates a no-op instrument.
 func (NopMeter) Float64Histogram(string, ...InstrumentOption) (Float64Histogram, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 // Float64AsyncCounter creates a no-op instrument.
 func (NopMeter) Float64AsyncCounter(string, Float64Callback, ...InstrumentOption) (AsyncInstrument, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 // Float64AsyncUpDownCounter creates a no-op instrument.
 func (NopMeter) Float64AsyncUpDownCounter(string, Float64Callback, ...InstrumentOption) (AsyncInstrument, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 // Float64AsyncGauge creates a no-op instrument.
 func (NopMeter) Float64AsyncGauge(string, Float64Callback, ...InstrumentOption) (AsyncInstrument, error) {
-	return nopInstrument[float64]{}, nil
+	return nopInstrumentFloat64, nil
 }
 
 type nopInstrument[N any] struct{}
@@ -93,3 +93,6 @@ func (nopInstrument[N]) Add(context.Context, N, ...RecordMetricOption)    {}
 func (nopInstrument[N]) Sample(context.Context, N, ...RecordMetricOption) {}
 func (nopInstrument[N]) Record(context.Context, N, ...RecordMetricOption) {}
 func (nopInstrument[_]) Stop()                                            {}
+
+var nopInstrumentInt64 = nopInstrument[int64]{}
+var nopInstrumentFloat64 = nopInstrument[float64]{}