Add Base2ExponentialHistogram example (#4518)

sdk/metric/aggregation.go

@@ -48,8 +48,8 @@ func (AggregationDrop) err() error { return nil }
 // make an aggregation selection based on instrument kind that differs from
 // the default. This Aggregation ensures the default is used.
 //
-// See the "go.opentelemetry.io/otel/sdk/metric".DefaultAggregationSelector
-// for information about the default instrument kind selection mapping.
+// See the [DefaultAggregationSelector] for information about the default
+// instrument kind selection mapping.
 type AggregationDefault struct{} // AggregationDefault has no parameters.
 
 var _ Aggregation = AggregationDefault{}
@@ -161,7 +161,7 @@ type AggregationBase2ExponentialHistogram struct {
 	// signed 32-bit integer index could be used.
 	//
 	// MaxScale has a minimum value of -10. Using a value of -10 means only
-	// two buckets will be use.
+	// two buckets will be used.
 	MaxScale int32
 
 	// NoMinMax indicates whether to not record the min and max of the

sdk/metric/example_test.go

@@ -85,6 +85,8 @@ func ExampleView() {
 
 	re := regexp.MustCompile(`[._](ms|byte)$`)
 	var view metric.View = func(i metric.Instrument) (metric.Stream, bool) {
+		// In a custom View function, you need to explicitly copy
+		// the name, description, and unit.
 		s := metric.Stream{Name: i.Name, Description: i.Description, Unit: i.Unit}
 		// Any instrument that does not have a unit suffix defined, but has a
 		// dimensional unit defined, update the name with a unit suffix.
@@ -220,3 +222,26 @@ func ExampleNewView_wildcard() {
 	// name: computation.time.ms
 	// unit: ms
 }
+
+func ExampleNewView_exponentialHistogram() {
+	// Create a view that makes the "latency" instrument
+	// to be reported as an exponential histogram.
+	view := metric.NewView(
+		metric.Instrument{
+			Name:  "latency",
+			Scope: instrumentation.Scope{Name: "http"},
+		},
+		metric.Stream{
+			Aggregation: metric.AggregationBase2ExponentialHistogram{
+				MaxSize:  160,
+				MaxScale: 20,
+			},
+		},
+	)
+
+	// The created view can then be registered with the OpenTelemetry metric
+	// SDK using the WithView option.
+	_ = metric.NewMeterProvider(
+		metric.WithView(view),
+	)
+}