Extract stats/view package.

Extract the exporting and view-related parts of the stats
package into a separate subpackage.

This reinforces the philosophy of separating stats collection
(which is in the stats package) and stats reporting, viewing,
and exporting (what you do with the collected stats).

README.md

@@ -113,7 +113,7 @@ Create and load measures with units:
 
 [embedmd]:# (stats.go measure)
 ```go
-videoSize, err := stats.NewMeasureInt64("my.org/video_size", "processed video size", "MB")
+videoSize, err := stats.NewInt64("my.org/video_size", "processed video size", "MB")
 if err != nil {
 	log.Fatal(err)
 }
@@ -129,18 +129,6 @@ if m == nil {
 }
 ```
 
-Delete measure (this can be useful when replacing a measure by
-another measure with the same name):
-
-[embedmd]:# (stats.go deleteMeasure)
-```go
-if err := stats.DeleteMeasure(m); err != nil {
-	log.Fatal(err)
-}
-```
-However, it is an error to delete a Measure that's used by at least one View. The
-View using the Measure has to be unregistered first.
-
 ### Creating an aggregation
 
 Currently 4 types of aggregations are supported. The CountAggregation is used to count
@@ -151,10 +139,10 @@ sample values.
 
 [embedmd]:# (stats.go aggs)
 ```go
-distAgg := stats.DistributionAggregation([]float64{0, 1 << 32, 2 << 32, 3 << 32})
-countAgg := stats.CountAggregation{}
-sumAgg := stats.SumAggregation{}
-meanAgg := stats.MeanAggregation{}
+distAgg := view.DistributionAggregation([]float64{0, 1 << 32, 2 << 32, 3 << 32})
+countAgg := view.CountAggregation{}
+sumAgg := view.SumAggregation{}
+meanAgg := view.MeanAggregation{}
 ```
 
 ### Create an aggregation window
@@ -163,7 +151,7 @@ Use Cumulative to continuously aggregate the recorded data.
 
 [embedmd]:# (stats.go windows)
 ```go
-cum := stats.Cumulative{}
+cum := view.Cumulative{}
 ```
 
 ### Creating, registering and unregistering a view
@@ -172,7 +160,7 @@ Create and register a view:
 
 [embedmd]:# (stats.go view)
 ```go
-view, err := stats.NewView(
+v, err := view.New(
 	"my.org/video_size_distribution",
 	"distribution of processed video size over time",
 	nil,
@@ -183,7 +171,7 @@ view, err := stats.NewView(
 if err != nil {
 	log.Fatalf("cannot create view: %v", err)
 }
-if err := stats.RegisterView(view); err != nil {
+if err := view.Register(v); err != nil {
 	log.Fatal(err)
 }
 ```
@@ -192,7 +180,7 @@ Find view by name:
 
 [embedmd]:# (stats.go findView)
 ```go
-v := stats.FindView("my.org/video_size_distribution")
+v = view.Find("my.org/video_size_distribution")
 if v == nil {
 	log.Fatalln("view not found")
 }
@@ -202,7 +190,7 @@ Unregister view:
 
 [embedmd]:# (stats.go unregisterView)
 ```go
-if err = stats.UnregisterView(v); err != nil {
+if err = view.Unregister(v); err != nil {
 	log.Fatal(err)
 }
 ```
@@ -214,7 +202,7 @@ a duration less than a certain minimum (maybe 1s) should have no effect.
 
 [embedmd]:# (stats.go reportingPeriod)
 ```go
-stats.SetReportingPeriod(5 * time.Second)
+view.SetReportingPeriod(5 * time.Second)
 ```
 
 ### Recording measurements
@@ -234,7 +222,7 @@ Users need to subscribe to a view in order to retrieve collected data.
 
 [embedmd]:# (stats.go subscribe)
 ```go
-if err := view.Subscribe(); err != nil {
+if err := v.Subscribe(); err != nil {
 	log.Fatal(err)
 }
 ```
@@ -245,7 +233,7 @@ Subscribed views' data will be exported via the registered exporters.
 ```go
 // Register an exporter to be able to retrieve
 // the data from the subscribed views.
-stats.RegisterExporter(&exporter{})
+view.RegisterExporter(&exporter{})
 ```
 
 An example logger exporter is below:
@@ -255,7 +243,7 @@ An example logger exporter is below:
 
 type exporter struct{}
 
-func (e *exporter) ExportView(vd *stats.ViewData) {
+func (e *exporter) ExportView(vd *view.Data) {
 	log.Println(vd)
 }
 

examples/grpc/exporter/exporter.go

@@ -17,7 +17,7 @@ package exporter
 import (
 	"log"
 
-	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
 	"go.opencensus.io/trace"
 )
 
@@ -26,7 +26,7 @@ import (
 type Exporter struct{}
 
 // ExportView logs the view data.
-func (e *Exporter) ExportView(vd *stats.ViewData) {
+func (e *Exporter) ExportView(vd *view.Data) {
 	log.Println(vd)
 }
 

examples/grpc/helloworld_client/main.go

@@ -24,7 +24,7 @@ import (
 	pb "go.opencensus.io/examples/grpc/proto"
 	ocgrpc "go.opencensus.io/plugin/grpc"
 	"go.opencensus.io/plugin/grpc/grpcstats"
-	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
 	"go.opencensus.io/zpages"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
@@ -41,7 +41,7 @@ func main() {
 
 	// Register stats and trace exporters to export
 	// the collected data.
-	stats.RegisterExporter(&exporter.Exporter{})
+	view.RegisterExporter(&exporter.Exporter{})
 
 	// Subscribe to collect client request count.
 	if err := grpcstats.RPCClientRequestCountView.Subscribe(); err != nil {
@@ -62,7 +62,7 @@ func main() {
 	if len(os.Args) > 1 {
 		name = os.Args[1]
 	}
-	stats.SetReportingPeriod(time.Second)
+	view.SetReportingPeriod(time.Second)
 	for {
 		r, err := c.SayHello(context.Background(), &pb.HelloRequest{Name: name})
 		if err != nil {

examples/grpc/helloworld_server/main.go

@@ -25,7 +25,7 @@ import (
 	pb "go.opencensus.io/examples/grpc/proto"
 	ocgrpc "go.opencensus.io/plugin/grpc"
 	"go.opencensus.io/plugin/grpc/grpcstats"
-	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
 	"go.opencensus.io/zpages"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
@@ -47,7 +47,7 @@ func main() {
 	go func() { log.Fatal(http.ListenAndServe(":8081", nil)) }()
 	// Register stats and trace exporters to export
 	// the collected data.
-	stats.RegisterExporter(&exporter.Exporter{})
+	view.RegisterExporter(&exporter.Exporter{})
 
 	// Subscribe to collect server request count.
 	if err := grpcstats.RPCServerRequestCountView.Subscribe(); err != nil {

examples/stats/helloworld/main.go

@@ -23,42 +23,43 @@ import (
 	"time"
 
 	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
 )
 
 func main() {
 	ctx := context.Background()
 
 	// Register an exporter to be able to retrieve
 	// the data from the subscribed views.
-	stats.RegisterExporter(&exporter{})
+	view.RegisterExporter(&exporter{})
 
 	// Create measures. The program will record measures for the size of
 	// processed videos and the nubmer of videos marked as spam.
-	videoSize, err := stats.NewMeasureInt64("my.org/measure/video_size", "size of processed videos", "MBy")
+	videoSize, err := stats.NewInt64("my.org/measure/video_size", "size of processed videos", "MBy")
 	if err != nil {
 		log.Fatalf("Video size measure not created: %v", err)
 	}
 
 	// Create view to see the processed video size
 	// distribution over 10 seconds.
-	view, err := stats.NewView(
+	v, err := view.New(
 		"my.org/views/video_size",
 		"processed video size over time",
 		nil,
 		videoSize,
-		stats.DistributionAggregation([]float64{0, 1 << 16, 1 << 32}),
-		stats.Cumulative{},
+		view.DistributionAggregation([]float64{0, 1 << 16, 1 << 32}),
+		view.Cumulative{},
 	)
 	if err != nil {
 		log.Fatalf("Cannot create view: %v", err)
 	}
 
 	// Set reporting period to report data at every second.
-	stats.SetReportingPeriod(1 * time.Second)
+	view.SetReportingPeriod(1 * time.Second)
 
 	// Subscribe will allow view data to be exported.
 	// Once no longer need, you can unsubscribe from the view.
-	if err := view.Subscribe(); err != nil {
+	if err := v.Subscribe(); err != nil {
 		log.Fatalf("Cannot subscribe to the view: %v", err)
 	}
 
@@ -73,6 +74,6 @@ func main() {
 
 type exporter struct{}
 
-func (e *exporter) ExportView(vd *stats.ViewData) {
+func (e *exporter) ExportView(vd *view.Data) {
 	log.Println(vd)
 }

examples/stats/prometheus/main.go

@@ -25,6 +25,7 @@ import (
 
 	"go.opencensus.io/exporter/prometheus"
 	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
 )
 
 func main() {
@@ -34,23 +35,23 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	stats.RegisterExporter(exporter)
+	view.RegisterExporter(exporter)
 
 	// Create measures. The program will record measures for the size of
 	// processed videos and the number of videos marked as spam.
-	videoCount, err := stats.NewMeasureInt64("my.org/measures/video_count", "number of processed videos", "")
+	videoCount, err := stats.NewInt64("my.org/measures/video_count", "number of processed videos", "")
 	if err != nil {
 		log.Fatalf("Video count measure not created: %v", err)
 	}
 
 	// 1. Create view to see the number of processed videos cumulatively.
-	viewCount, err := stats.NewView(
+	viewCount, err := view.New(
 		"video_count",
 		"number of videos processed over time",
 		nil,
 		videoCount,
-		stats.CountAggregation{},
-		stats.Cumulative{},
+		view.CountAggregation{},
+		view.Cumulative{},
 	)
 	if err != nil {
 		log.Fatalf("Cannot create view: %v", err)
@@ -64,19 +65,19 @@ func main() {
 
 	// Create measures. The program will record measures for the size of
 	// processed videos and the number of videos marked as spam.
-	videoSize, err := stats.NewMeasureInt64("my.org/measures/video_size_cum", "size of processed video", "MBy")
+	videoSize, err := stats.NewInt64("my.org/measures/video_size_cum", "size of processed video", "MBy")
 	if err != nil {
 		log.Fatalf("Video size measure not created: %v", err)
 	}
 
 	// 2. Create view to see the amount of video processed
-	viewSize, err := stats.NewView(
+	viewSize, err := view.New(
 		"video_cum",
 		"processed video size over time",
 		nil,
 		videoSize,
-		stats.DistributionAggregation([]float64{0, 1 << 16, 1 << 32}),
-		stats.Cumulative{},
+		view.DistributionAggregation([]float64{0, 1 << 16, 1 << 32}),
+		view.Cumulative{},
 	)
 	if err != nil {
 		log.Fatalf("Cannot create view: %v", err)
@@ -89,7 +90,7 @@ func main() {
 	}
 
 	// Set reporting period to report data at every second.
-	stats.SetReportingPeriod(1 * time.Second)
+	view.SetReportingPeriod(1 * time.Second)
 
 	// Record some data points...
 	go func() {

examples/stats/stackdriver/main.go

@@ -25,6 +25,7 @@ import (
 
 	"go.opencensus.io/exporter/stackdriver"
 	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
 )
 
 func main() {
@@ -46,34 +47,34 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	stats.RegisterExporter(exporter)
+	view.RegisterExporter(exporter)
 
 	// Create measures. The program will record measures for the size of
 	// processed videos and the nubmer of videos marked as spam.
-	videoSize, err := stats.NewMeasureInt64("my.org/measure/video_size", "size of processed videos", "MBy")
+	videoSize, err := stats.NewInt64("my.org/measure/video_size", "size of processed videos", "MBy")
 	if err != nil {
 		log.Fatalf("Video size measure not created: %v", err)
 	}
 
 	// Create view to see the processed video size cumulatively.
-	view, err := stats.NewView(
+	v, err := view.New(
 		"my.org/views/video_size_cum",
 		"processed video size over time",
 		nil,
 		videoSize,
-		stats.DistributionAggregation([]float64{0, 1 << 16, 1 << 32}),
-		stats.Cumulative{},
+		view.DistributionAggregation([]float64{0, 1 << 16, 1 << 32}),
+		view.Cumulative{},
 	)
 	if err != nil {
 		log.Fatalf("Cannot create view: %v", err)
 	}
 
 	// Set reporting period to report data at every second.
-	stats.SetReportingPeriod(1 * time.Second)
+	view.SetReportingPeriod(1 * time.Second)
 
 	// Subscribe will allow view data to be exported.
 	// Once no longer need, you can unsubscribe from the view.
-	if err := view.Subscribe(); err != nil {
+	if err := v.Subscribe(); err != nil {
 		log.Fatalf("Cannot subscribe to the view: %v", err)
 	}