From f90057a4fabdb83f2c3cb810f02a4daf8a0375ca Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 10:31:50 +1100
Subject: [PATCH 1/9] move Metric Aggregator/Aggregation/AggretorSelector from
 otel/sdk/export/metric to otel/metric

---
 exporters/metric/prometheus/prometheus.go     |   2 +-
 exporters/otlp/internal/transform/metric.go   |   2 +-
 .../otlp/internal/transform/metric_test.go    |   8 +-
 exporters/otlp/otlp.go                        |   2 +-
 exporters/otlp/otlp_metric_test.go            |   4 +-
 exporters/stdout/metric.go                    |   2 +-
 exporters/stdout/metric_test.go               |   2 +-
 .../aggregation/aggregation.go                |   0
 metric/metric_aggregator.go                   | 108 ++++++++++++++++++
 sdk/export/metric/exportkind_test.go          |   2 +-
 sdk/export/metric/metric.go                   |  99 +---------------
 sdk/export/metric/metrictest/test.go          |  18 +--
 sdk/metric/aggregator/aggregator.go           |   5 +-
 sdk/metric/aggregator/aggregator_test.go      |   2 +-
 sdk/metric/aggregator/aggregatortest/test.go  |  15 ++-
 sdk/metric/aggregator/exact/exact.go          |   9 +-
 sdk/metric/aggregator/exact/exact_test.go     |   5 +-
 sdk/metric/aggregator/histogram/histogram.go  |   9 +-
 .../aggregator/histogram/histogram_test.go    |   3 +-
 sdk/metric/aggregator/lastvalue/lastvalue.go  |   9 +-
 .../aggregator/lastvalue/lastvalue_test.go    |   7 +-
 sdk/metric/aggregator/minmaxsumcount/mmsc.go  |   9 +-
 .../aggregator/minmaxsumcount/mmsc_test.go    |   5 +-
 sdk/metric/aggregator/sum/sum.go              |  10 +-
 sdk/metric/aggregator/sum/sum_test.go         |   3 +-
 sdk/metric/benchmark_test.go                  |   2 +-
 .../controller/basic/controller_test.go       |   2 +-
 sdk/metric/controller/basic/push_test.go      |   2 +-
 sdk/metric/correct_test.go                    |   6 +-
 sdk/metric/processor/basic/basic.go           |  12 +-
 sdk/metric/processor/basic/basic_test.go      |   8 +-
 sdk/metric/processor/processortest/test.go    |  16 +--
 sdk/metric/sdk.go                             |  10 +-
 sdk/metric/selector/simple/simple.go          |  23 ++--
 sdk/metric/selector/simple/simple_test.go     |   7 +-
 sdk/metric/stress_test.go                     |   4 +-
 36 files changed, 220 insertions(+), 212 deletions(-)
 rename {sdk/export/metric => metric}/aggregation/aggregation.go (100%)
 create mode 100644 metric/metric_aggregator.go

diff --git a/exporters/metric/prometheus/prometheus.go b/exporters/metric/prometheus/prometheus.go
index e74f6524737..8c966d99b76 100644
--- a/exporters/metric/prometheus/prometheus.go
+++ b/exporters/metric/prometheus/prometheus.go
@@ -29,9 +29,9 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 	controller "go.opentelemetry.io/otel/sdk/metric/controller/basic"
 	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
diff --git a/exporters/otlp/internal/transform/metric.go b/exporters/otlp/internal/transform/metric.go
index ca913457950..f041a5f08e1 100644
--- a/exporters/otlp/internal/transform/metric.go
+++ b/exporters/otlp/internal/transform/metric.go
@@ -29,9 +29,9 @@ import (
 	resourcepb "go.opentelemetry.io/otel/exporters/otlp/internal/opentelemetry-proto-gen/resource/v1"
 
 	"go.opentelemetry.io/otel/label"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
diff --git a/exporters/otlp/internal/transform/metric_test.go b/exporters/otlp/internal/transform/metric_test.go
index a6698666550..8b85c709db6 100644
--- a/exporters/otlp/internal/transform/metric_test.go
+++ b/exporters/otlp/internal/transform/metric_test.go
@@ -28,9 +28,9 @@ import (
 	metricpb "go.opentelemetry.io/otel/exporters/otlp/internal/opentelemetry-proto-gen/metrics/v1"
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/export/metric/metrictest"
 	arrAgg "go.opentelemetry.io/otel/sdk/metric/aggregator/exact"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
@@ -328,10 +328,10 @@ func (t *testAgg) Aggregation() aggregation.Aggregation {
 func (t *testAgg) Update(ctx context.Context, number number.Number, descriptor *metric.Descriptor) error {
 	return nil
 }
-func (t *testAgg) SynchronizedMove(destination export.Aggregator, descriptor *metric.Descriptor) error {
+func (t *testAgg) SynchronizedMove(destination metric.Aggregator, descriptor *metric.Descriptor) error {
 	return nil
 }
-func (t *testAgg) Merge(aggregator export.Aggregator, descriptor *metric.Descriptor) error {
+func (t *testAgg) Merge(aggregator metric.Aggregator, descriptor *metric.Descriptor) error {
 	return nil
 }
 
@@ -373,7 +373,7 @@ func (te *testErrMinMaxSumCount) Count() (uint64, error) {
 	return 0, te.err
 }
 
-var _ export.Aggregator = &testAgg{}
+var _ metric.Aggregator = &testAgg{}
 var _ aggregation.Aggregation = &testAgg{}
 var _ aggregation.Sum = &testErrSum{}
 var _ aggregation.LastValue = &testErrLastValue{}
diff --git a/exporters/otlp/otlp.go b/exporters/otlp/otlp.go
index 3380d6c2933..6bc488fe5d0 100644
--- a/exporters/otlp/otlp.go
+++ b/exporters/otlp/otlp.go
@@ -20,8 +20,8 @@ import (
 	"sync"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	metricsdk "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	tracesdk "go.opentelemetry.io/otel/sdk/export/trace"
 )
 
diff --git a/exporters/otlp/otlp_metric_test.go b/exporters/otlp/otlp_metric_test.go
index 3da92f098ab..59598a7bfa5 100644
--- a/exporters/otlp/otlp_metric_test.go
+++ b/exporters/otlp/otlp_metric_test.go
@@ -29,9 +29,9 @@ import (
 	resourcepb "go.opentelemetry.io/otel/exporters/otlp/internal/opentelemetry-proto-gen/resource/v1"
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	metricsdk "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/export/metric/metrictest"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/sum"
@@ -752,7 +752,7 @@ func runMetricExportTests(t *testing.T, opts []otlp.ExporterOption, rs []record,
 		desc := metric.NewDescriptor(r.name, r.iKind, r.nKind, r.opts...)
 		labs := label.NewSet(lcopy...)
 
-		var agg, ckpt metricsdk.Aggregator
+		var agg, ckpt metric.Aggregator
 		if r.iKind.Adding() {
 			agg, ckpt = metrictest.Unslice2(sum.New(2))
 		} else {
diff --git a/exporters/stdout/metric.go b/exporters/stdout/metric.go
index 9b183a0022d..5d640c44083 100644
--- a/exporters/stdout/metric.go
+++ b/exporters/stdout/metric.go
@@ -23,8 +23,8 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	exportmetric "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 )
 
 type metricExporter struct {
diff --git a/exporters/stdout/metric_test.go b/exporters/stdout/metric_test.go
index d5ebcfca864..d134c7dab2a 100644
--- a/exporters/stdout/metric_test.go
+++ b/exporters/stdout/metric_test.go
@@ -212,7 +212,7 @@ func TestStdoutValueRecorderFormat(t *testing.T) {
 func TestStdoutNoData(t *testing.T) {
 	desc := metric.NewDescriptor("test.name", metric.ValueRecorderInstrumentKind, number.Float64Kind)
 
-	runTwoAggs := func(agg, ckpt export.Aggregator) {
+	runTwoAggs := func(agg, ckpt metric.Aggregator) {
 		t.Run(fmt.Sprintf("%T", agg), func(t *testing.T) {
 			t.Parallel()
 
diff --git a/sdk/export/metric/aggregation/aggregation.go b/metric/aggregation/aggregation.go
similarity index 100%
rename from sdk/export/metric/aggregation/aggregation.go
rename to metric/aggregation/aggregation.go
diff --git a/metric/metric_aggregator.go b/metric/metric_aggregator.go
new file mode 100644
index 00000000000..21074bb62f4
--- /dev/null
+++ b/metric/metric_aggregator.go
@@ -0,0 +1,108 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metric // import "go.opentelemetry.io/otel/metric"
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/metric/aggregation"
+	"go.opentelemetry.io/otel/metric/number"
+)
+
+// Aggregator implements a specific aggregation behavior, e.g., a
+// behavior to track a sequence of updates to an instrument.  Sum-only
+// instruments commonly use a simple Sum aggregator, but for the
+// distribution instruments (ValueRecorder, ValueObserver) there are a
+// number of possible aggregators with different cost and accuracy
+// tradeoffs.
+//
+// Note that any Aggregator may be attached to any instrument--this is
+// the result of the OpenTelemetry API/SDK separation.  It is possible
+// to attach a Sum aggregator to a ValueRecorder instrument or a
+// MinMaxSumCount aggregator to a Counter instrument.
+type Aggregator interface {
+	// Aggregation returns an Aggregation interface to access the
+	// current state of this Aggregator.  The caller is
+	// responsible for synchronization and must not call any the
+	// other methods in this interface concurrently while using
+	// the Aggregation.
+	Aggregation() aggregation.Aggregation
+
+	// Update receives a new measured value and incorporates it
+	// into the aggregation.  Update() calls may be called
+	// concurrently.
+	//
+	// Descriptor.NumberKind() should be consulted to determine
+	// whether the provided number is an int64 or float64.
+	//
+	// The Context argument comes from user-level code and could be
+	// inspected for a `correlation.Map` or `trace.SpanContext`.
+	Update(ctx context.Context, number number.Number, descriptor *Descriptor) error
+
+	// SynchronizedMove is called during collection to finish one
+	// period of aggregation by atomically saving the
+	// currently-updating state into the argument Aggregator AND
+	// resetting the current value to the zero state.
+	//
+	// SynchronizedMove() is called concurrently with Update().  These
+	// two methods must be synchronized with respect to each
+	// other, for correctness.
+	//
+	// After saving a synchronized copy, the Aggregator can be converted
+	// into one or more of the interfaces in the `aggregation` sub-package,
+	// according to kind of Aggregator that was selected.
+	//
+	// This method will return an InconsistentAggregatorError if
+	// this Aggregator cannot be copied into the destination due
+	// to an incompatible type.
+	//
+	// This call has no Context argument because it is expected to
+	// perform only computation.
+	//
+	// When called with a nil `destination`, this Aggregator is reset
+	// and the current value is discarded.
+	SynchronizedMove(destination Aggregator, descriptor *Descriptor) error
+
+	// Merge combines the checkpointed state from the argument
+	// Aggregator into this Aggregator.  Merge is not synchronized
+	// with respect to Update or SynchronizedMove.
+	//
+	// The owner of an Aggregator being merged is responsible for
+	// synchronization of both Aggregator states.
+	Merge(aggregator Aggregator, descriptor *Descriptor) error
+}
+
+// AggregatorSelector supports selecting the kind of Aggregator to
+// use at runtime for a specific metric instrument.
+type AggregatorSelector interface {
+	// AggregatorFor allocates a variable number of aggregators of
+	// a kind suitable for the requested export.  This method
+	// initializes a `...*Aggregator`, to support making a single
+	// allocation.
+	//
+	// When the call returns without initializing the *Aggregator
+	// to a non-nil value, the metric instrument is explicitly
+	// disabled.
+	//
+	// This must return a consistent type to avoid confusion in
+	// later stages of the metrics export process, i.e., when
+	// Merging or Checkpointing aggregators for a specific
+	// instrument.
+	//
+	// Note: This is context-free because the aggregator should
+	// not relate to the incoming context.  This call should not
+	// block.
+	AggregatorFor(descriptor *Descriptor, aggregator ...*Aggregator)
+}
diff --git a/sdk/export/metric/exportkind_test.go b/sdk/export/metric/exportkind_test.go
index acaa12cd1dc..87ee959fe55 100644
--- a/sdk/export/metric/exportkind_test.go
+++ b/sdk/export/metric/exportkind_test.go
@@ -20,8 +20,8 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 )
 
 func TestExportKindIncludes(t *testing.T) {
diff --git a/sdk/export/metric/metric.go b/sdk/export/metric/metric.go
index 525fe8f3a63..b1f01a6ec93 100644
--- a/sdk/export/metric/metric.go
+++ b/sdk/export/metric/metric.go
@@ -23,8 +23,7 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
-	"go.opentelemetry.io/otel/metric/number"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
@@ -63,7 +62,7 @@ type Processor interface {
 	// Note that the SDK only calls AggregatorFor when new records
 	// require an Aggregator. This does not provide a way to
 	// disable metrics with active records.
-	AggregatorSelector
+	metric.AggregatorSelector
 
 	// Process is called by the SDK once per internal record,
 	// passing the export Accumulation (a Descriptor, the corresponding
@@ -75,29 +74,6 @@ type Processor interface {
 	Process(accum Accumulation) error
 }
 
-// AggregatorSelector supports selecting the kind of Aggregator to
-// use at runtime for a specific metric instrument.
-type AggregatorSelector interface {
-	// AggregatorFor allocates a variable number of aggregators of
-	// a kind suitable for the requested export.  This method
-	// initializes a `...*Aggregator`, to support making a single
-	// allocation.
-	//
-	// When the call returns without initializing the *Aggregator
-	// to a non-nil value, the metric instrument is explicitly
-	// disabled.
-	//
-	// This must return a consistent type to avoid confusion in
-	// later stages of the metrics export process, i.e., when
-	// Merging or Checkpointing aggregators for a specific
-	// instrument.
-	//
-	// Note: This is context-free because the aggregator should
-	// not relate to the incoming context.  This call should not
-	// block.
-	AggregatorFor(descriptor *metric.Descriptor, aggregator ...*Aggregator)
-}
-
 // Checkpointer is the interface used by a Controller to coordinate
 // the Processor with Accumulator(s) and Exporter(s).  The
 // StartCollection() and FinishCollection() methods start and finish a
@@ -125,69 +101,6 @@ type Checkpointer interface {
 	FinishCollection() error
 }
 
-// Aggregator implements a specific aggregation behavior, e.g., a
-// behavior to track a sequence of updates to an instrument.  Sum-only
-// instruments commonly use a simple Sum aggregator, but for the
-// distribution instruments (ValueRecorder, ValueObserver) there are a
-// number of possible aggregators with different cost and accuracy
-// tradeoffs.
-//
-// Note that any Aggregator may be attached to any instrument--this is
-// the result of the OpenTelemetry API/SDK separation.  It is possible
-// to attach a Sum aggregator to a ValueRecorder instrument or a
-// MinMaxSumCount aggregator to a Counter instrument.
-type Aggregator interface {
-	// Aggregation returns an Aggregation interface to access the
-	// current state of this Aggregator.  The caller is
-	// responsible for synchronization and must not call any the
-	// other methods in this interface concurrently while using
-	// the Aggregation.
-	Aggregation() aggregation.Aggregation
-
-	// Update receives a new measured value and incorporates it
-	// into the aggregation.  Update() calls may be called
-	// concurrently.
-	//
-	// Descriptor.NumberKind() should be consulted to determine
-	// whether the provided number is an int64 or float64.
-	//
-	// The Context argument comes from user-level code and could be
-	// inspected for a `correlation.Map` or `trace.SpanContext`.
-	Update(ctx context.Context, number number.Number, descriptor *metric.Descriptor) error
-
-	// SynchronizedMove is called during collection to finish one
-	// period of aggregation by atomically saving the
-	// currently-updating state into the argument Aggregator AND
-	// resetting the current value to the zero state.
-	//
-	// SynchronizedMove() is called concurrently with Update().  These
-	// two methods must be synchronized with respect to each
-	// other, for correctness.
-	//
-	// After saving a synchronized copy, the Aggregator can be converted
-	// into one or more of the interfaces in the `aggregation` sub-package,
-	// according to kind of Aggregator that was selected.
-	//
-	// This method will return an InconsistentAggregatorError if
-	// this Aggregator cannot be copied into the destination due
-	// to an incompatible type.
-	//
-	// This call has no Context argument because it is expected to
-	// perform only computation.
-	//
-	// When called with a nil `destination`, this Aggregator is reset
-	// and the current value is discarded.
-	SynchronizedMove(destination Aggregator, descriptor *metric.Descriptor) error
-
-	// Merge combines the checkpointed state from the argument
-	// Aggregator into this Aggregator.  Merge is not synchronized
-	// with respect to Update or SynchronizedMove.
-	//
-	// The owner of an Aggregator being merged is responsible for
-	// synchronization of both Aggregator states.
-	Merge(aggregator Aggregator, descriptor *metric.Descriptor) error
-}
-
 // Subtractor is an optional interface implemented by some
 // Aggregators.  An Aggregator must support `Subtract()` in order to
 // be configured for a Precomputed-Sum instrument (SumObserver,
@@ -195,7 +108,7 @@ type Aggregator interface {
 type Subtractor interface {
 	// Subtract subtracts the `operand` from this Aggregator and
 	// outputs the value in `result`.
-	Subtract(operand, result Aggregator, descriptor *metric.Descriptor) error
+	Subtract(operand, result metric.Aggregator, descriptor *metric.Descriptor) error
 }
 
 // Exporter handles presentation of the checkpoint of aggregate
@@ -275,7 +188,7 @@ type Metadata struct {
 // and label set, as prepared by an Accumulator for the Processor.
 type Accumulation struct {
 	Metadata
-	aggregator Aggregator
+	aggregator metric.Aggregator
 }
 
 // Record contains the exported data for a single metric instrument
@@ -308,7 +221,7 @@ func (m Metadata) Resource() *resource.Resource {
 // Accumulations to send to Processors. The Descriptor, Labels, Resource,
 // and Aggregator represent aggregate metric events received over a single
 // collection period.
-func NewAccumulation(descriptor *metric.Descriptor, labels *label.Set, resource *resource.Resource, aggregator Aggregator) Accumulation {
+func NewAccumulation(descriptor *metric.Descriptor, labels *label.Set, resource *resource.Resource, aggregator metric.Aggregator) Accumulation {
 	return Accumulation{
 		Metadata: Metadata{
 			descriptor: descriptor,
@@ -321,7 +234,7 @@ func NewAccumulation(descriptor *metric.Descriptor, labels *label.Set, resource
 
 // Aggregator returns the checkpointed aggregator. It is safe to
 // access the checkpointed state without locking.
-func (r Accumulation) Aggregator() Aggregator {
+func (r Accumulation) Aggregator() metric.Aggregator {
 	return r.aggregator
 }
 
diff --git a/sdk/export/metric/metrictest/test.go b/sdk/export/metric/metrictest/test.go
index 9905300d893..ca3a45d3d1a 100644
--- a/sdk/export/metric/metrictest/test.go
+++ b/sdk/export/metric/metrictest/test.go
@@ -23,9 +23,9 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
@@ -46,7 +46,7 @@ type CheckpointSet struct {
 // NoopAggregator is useful for testing Exporters.
 type NoopAggregator struct{}
 
-var _ export.Aggregator = (*NoopAggregator)(nil)
+var _ metric.Aggregator = (*NoopAggregator)(nil)
 
 // Update implements export.Aggregator.
 func (NoopAggregator) Update(context.Context, number.Number, *metric.Descriptor) error {
@@ -54,12 +54,12 @@ func (NoopAggregator) Update(context.Context, number.Number, *metric.Descriptor)
 }
 
 // SynchronizedMove implements export.Aggregator.
-func (NoopAggregator) SynchronizedMove(export.Aggregator, *metric.Descriptor) error {
+func (NoopAggregator) SynchronizedMove(metric.Aggregator, *metric.Descriptor) error {
 	return nil
 }
 
 // Merge implements export.Aggregator.
-func (NoopAggregator) Merge(export.Aggregator, *metric.Descriptor) error {
+func (NoopAggregator) Merge(metric.Aggregator, *metric.Descriptor) error {
 	return nil
 }
 
@@ -92,7 +92,7 @@ func (p *CheckpointSet) Reset() {
 //
 // If there is an existing record with the same descriptor and labels,
 // the stored aggregator will be returned and should be merged.
-func (p *CheckpointSet) Add(desc *metric.Descriptor, newAgg export.Aggregator, labels ...label.KeyValue) (agg export.Aggregator, added bool) {
+func (p *CheckpointSet) Add(desc *metric.Descriptor, newAgg metric.Aggregator, labels ...label.KeyValue) (agg metric.Aggregator, added bool) {
 	elabels := label.NewSet(labels...)
 
 	key := mapkey{
@@ -100,7 +100,7 @@ func (p *CheckpointSet) Add(desc *metric.Descriptor, newAgg export.Aggregator, l
 		distinct: elabels.Equivalent(),
 	}
 	if record, ok := p.records[key]; ok {
-		return record.Aggregation().(export.Aggregator), false
+		return record.Aggregation().(metric.Aggregator), false
 	}
 
 	rec := export.NewRecord(desc, &elabels, p.resource, newAgg.Aggregation(), time.Time{}, time.Time{})
@@ -121,7 +121,7 @@ func (p *CheckpointSet) ForEach(_ export.ExportKindSelector, f func(export.Recor
 }
 
 // Takes a slice of []some.Aggregator and returns a slice of []export.Aggregator
-func Unslice2(sl interface{}) (one, two export.Aggregator) {
+func Unslice2(sl interface{}) (one, two metric.Aggregator) {
 	slv := reflect.ValueOf(sl)
 	if slv.Type().Kind() != reflect.Slice {
 		panic("Invalid Unslice2")
@@ -129,7 +129,7 @@ func Unslice2(sl interface{}) (one, two export.Aggregator) {
 	if slv.Len() != 2 {
 		panic("Invalid Unslice2: length > 2")
 	}
-	one = slv.Index(0).Addr().Interface().(export.Aggregator)
-	two = slv.Index(1).Addr().Interface().(export.Aggregator)
+	one = slv.Index(0).Addr().Interface().(metric.Aggregator)
+	two = slv.Index(1).Addr().Interface().(metric.Aggregator)
 	return
 }
diff --git a/sdk/metric/aggregator/aggregator.go b/sdk/metric/aggregator/aggregator.go
index afda991e863..f0c06d29e97 100644
--- a/sdk/metric/aggregator/aggregator.go
+++ b/sdk/metric/aggregator/aggregator.go
@@ -19,15 +19,14 @@ import (
 	"math"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 )
 
 // NewInconsistentAggregatorError formats an error describing an attempt to
 // Checkpoint or Merge different-type aggregators.  The result can be unwrapped as
 // an ErrInconsistentType.
-func NewInconsistentAggregatorError(a1, a2 export.Aggregator) error {
+func NewInconsistentAggregatorError(a1, a2 metric.Aggregator) error {
 	return fmt.Errorf("%w: %T and %T", aggregation.ErrInconsistentType, a1, a2)
 }
 
diff --git a/sdk/metric/aggregator/aggregator_test.go b/sdk/metric/aggregator/aggregator_test.go
index 674d08cd03c..d15f268b3b8 100644
--- a/sdk/metric/aggregator/aggregator_test.go
+++ b/sdk/metric/aggregator/aggregator_test.go
@@ -22,8 +22,8 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/sum"
diff --git a/sdk/metric/aggregator/aggregatortest/test.go b/sdk/metric/aggregator/aggregatortest/test.go
index 268bea0d331..41125ec423a 100644
--- a/sdk/metric/aggregator/aggregatortest/test.go
+++ b/sdk/metric/aggregator/aggregatortest/test.go
@@ -27,9 +27,8 @@ import (
 
 	ottest "go.opentelemetry.io/otel/internal/internaltest"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 )
 
@@ -43,7 +42,7 @@ type Profile struct {
 type NoopAggregator struct{}
 type NoopAggregation struct{}
 
-var _ export.Aggregator = NoopAggregator{}
+var _ metric.Aggregator = NoopAggregator{}
 var _ aggregation.Aggregation = NoopAggregation{}
 
 func newProfiles() []Profile {
@@ -149,7 +148,7 @@ func (n *Numbers) Points() []number.Number {
 }
 
 // Performs the same range test the SDK does on behalf of the aggregator.
-func CheckedUpdate(t *testing.T, agg export.Aggregator, number number.Number, descriptor *metric.Descriptor) {
+func CheckedUpdate(t *testing.T, agg metric.Aggregator, number number.Number, descriptor *metric.Descriptor) {
 	ctx := context.Background()
 
 	// Note: Aggregator tests are written assuming that the SDK
@@ -165,7 +164,7 @@ func CheckedUpdate(t *testing.T, agg export.Aggregator, number number.Number, de
 	}
 }
 
-func CheckedMerge(t *testing.T, aggInto, aggFrom export.Aggregator, descriptor *metric.Descriptor) {
+func CheckedMerge(t *testing.T, aggInto, aggFrom metric.Aggregator, descriptor *metric.Descriptor) {
 	if err := aggInto.Merge(aggFrom, descriptor); err != nil {
 		t.Error("Unexpected Merge failure", err)
 	}
@@ -183,15 +182,15 @@ func (NoopAggregator) Update(context.Context, number.Number, *metric.Descriptor)
 	return nil
 }
 
-func (NoopAggregator) SynchronizedMove(export.Aggregator, *metric.Descriptor) error {
+func (NoopAggregator) SynchronizedMove(metric.Aggregator, *metric.Descriptor) error {
 	return nil
 }
 
-func (NoopAggregator) Merge(export.Aggregator, *metric.Descriptor) error {
+func (NoopAggregator) Merge(metric.Aggregator, *metric.Descriptor) error {
 	return nil
 }
 
-func SynchronizedMoveResetTest(t *testing.T, mkind metric.InstrumentKind, nf func(*metric.Descriptor) export.Aggregator) {
+func SynchronizedMoveResetTest(t *testing.T, mkind metric.InstrumentKind, nf func(*metric.Descriptor) metric.Aggregator) {
 	t.Run("reset on nil", func(t *testing.T) {
 		// Ensures that SynchronizedMove(nil, descriptor) discards and
 		// resets the aggregator.
diff --git a/sdk/metric/aggregator/exact/exact.go b/sdk/metric/aggregator/exact/exact.go
index c2c7adaf256..4302ebc6e8f 100644
--- a/sdk/metric/aggregator/exact/exact.go
+++ b/sdk/metric/aggregator/exact/exact.go
@@ -20,9 +20,8 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 )
 
@@ -35,7 +34,7 @@ type (
 	}
 )
 
-var _ export.Aggregator = &Aggregator{}
+var _ metric.Aggregator = &Aggregator{}
 var _ aggregation.Points = &Aggregator{}
 var _ aggregation.Count = &Aggregator{}
 
@@ -68,7 +67,7 @@ func (c *Aggregator) Points() ([]aggregation.Point, error) {
 
 // SynchronizedMove saves the current state to oa and resets the current state to
 // the empty set, taking a lock to prevent concurrent Update() calls.
-func (c *Aggregator) SynchronizedMove(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) SynchronizedMove(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 
 	if oa != nil && o == nil {
@@ -102,7 +101,7 @@ func (c *Aggregator) Update(_ context.Context, number number.Number, desc *metri
 }
 
 // Merge combines two data sets into one.
-func (c *Aggregator) Merge(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) Merge(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 	if o == nil {
 		return aggregator.NewInconsistentAggregatorError(c, oa)
diff --git a/sdk/metric/aggregator/exact/exact_test.go b/sdk/metric/aggregator/exact/exact_test.go
index 9a90d03ed68..1da7b117470 100644
--- a/sdk/metric/aggregator/exact/exact_test.go
+++ b/sdk/metric/aggregator/exact/exact_test.go
@@ -23,9 +23,8 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/aggregatortest"
 )
 
@@ -293,7 +292,7 @@ func TestSynchronizedMoveReset(t *testing.T) {
 	aggregatortest.SynchronizedMoveResetTest(
 		t,
 		metric.ValueRecorderInstrumentKind,
-		func(desc *metric.Descriptor) export.Aggregator {
+		func(desc *metric.Descriptor) metric.Aggregator {
 			return &New(1)[0]
 		},
 	)
diff --git a/sdk/metric/aggregator/histogram/histogram.go b/sdk/metric/aggregator/histogram/histogram.go
index ea3ecdbb5b2..a07e18b1c59 100644
--- a/sdk/metric/aggregator/histogram/histogram.go
+++ b/sdk/metric/aggregator/histogram/histogram.go
@@ -20,9 +20,8 @@ import (
 	"sync"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 )
 
@@ -97,7 +96,7 @@ var defaultInt64ExplicitBoundaries = func(bounds []float64) (asint []float64) {
 	return
 }(defaultFloat64ExplicitBoundaries)
 
-var _ export.Aggregator = &Aggregator{}
+var _ metric.Aggregator = &Aggregator{}
 var _ aggregation.Sum = &Aggregator{}
 var _ aggregation.Count = &Aggregator{}
 var _ aggregation.Histogram = &Aggregator{}
@@ -174,7 +173,7 @@ func (c *Aggregator) Histogram() (aggregation.Buckets, error) {
 // the empty set.  Since no locks are taken, there is a chance that
 // the independent Sum, Count and Bucket Count are not consistent with each
 // other.
-func (c *Aggregator) SynchronizedMove(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) SynchronizedMove(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 
 	if oa != nil && o == nil {
@@ -254,7 +253,7 @@ func (c *Aggregator) Update(_ context.Context, number number.Number, desc *metri
 }
 
 // Merge combines two histograms that have the same buckets into a single one.
-func (c *Aggregator) Merge(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) Merge(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 	if o == nil {
 		return aggregator.NewInconsistentAggregatorError(c, oa)
diff --git a/sdk/metric/aggregator/histogram/histogram_test.go b/sdk/metric/aggregator/histogram/histogram_test.go
index ddc2195167e..2edef165137 100644
--- a/sdk/metric/aggregator/histogram/histogram_test.go
+++ b/sdk/metric/aggregator/histogram/histogram_test.go
@@ -25,7 +25,6 @@ import (
 
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/aggregatortest"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 )
@@ -240,7 +239,7 @@ func TestSynchronizedMoveReset(t *testing.T) {
 	aggregatortest.SynchronizedMoveResetTest(
 		t,
 		metric.ValueRecorderInstrumentKind,
-		func(desc *metric.Descriptor) export.Aggregator {
+		func(desc *metric.Descriptor) metric.Aggregator {
 			return &histogram.New(1, desc, histogram.WithExplicitBoundaries(testBoundaries))[0]
 		},
 	)
diff --git a/sdk/metric/aggregator/lastvalue/lastvalue.go b/sdk/metric/aggregator/lastvalue/lastvalue.go
index 3cc5f7055cf..e43636bc712 100644
--- a/sdk/metric/aggregator/lastvalue/lastvalue.go
+++ b/sdk/metric/aggregator/lastvalue/lastvalue.go
@@ -21,9 +21,8 @@ import (
 	"unsafe"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 )
 
@@ -51,7 +50,7 @@ type (
 	}
 )
 
-var _ export.Aggregator = &Aggregator{}
+var _ metric.Aggregator = &Aggregator{}
 var _ aggregation.LastValue = &Aggregator{}
 
 // An unset lastValue has zero timestamp and zero value.
@@ -92,7 +91,7 @@ func (g *Aggregator) LastValue() (number.Number, time.Time, error) {
 }
 
 // SynchronizedMove atomically saves the current value.
-func (g *Aggregator) SynchronizedMove(oa export.Aggregator, _ *metric.Descriptor) error {
+func (g *Aggregator) SynchronizedMove(oa metric.Aggregator, _ *metric.Descriptor) error {
 	if oa == nil {
 		atomic.StorePointer(&g.value, unsafe.Pointer(unsetLastValue))
 		return nil
@@ -117,7 +116,7 @@ func (g *Aggregator) Update(_ context.Context, number number.Number, desc *metri
 
 // Merge combines state from two aggregators.  The most-recently set
 // value is chosen.
-func (g *Aggregator) Merge(oa export.Aggregator, desc *metric.Descriptor) error {
+func (g *Aggregator) Merge(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 	if o == nil {
 		return aggregator.NewInconsistentAggregatorError(g, oa)
diff --git a/sdk/metric/aggregator/lastvalue/lastvalue_test.go b/sdk/metric/aggregator/lastvalue/lastvalue_test.go
index 94baa69b71d..e8739a383db 100644
--- a/sdk/metric/aggregator/lastvalue/lastvalue_test.go
+++ b/sdk/metric/aggregator/lastvalue/lastvalue_test.go
@@ -26,15 +26,14 @@ import (
 
 	ottest "go.opentelemetry.io/otel/internal/internaltest"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/aggregatortest"
 )
 
 const count = 100
 
-var _ export.Aggregator = &Aggregator{}
+var _ metric.Aggregator = &Aggregator{}
 
 // Ensure struct alignment prior to running tests.
 func TestMain(m *testing.M) {
@@ -137,7 +136,7 @@ func TestSynchronizedMoveReset(t *testing.T) {
 	aggregatortest.SynchronizedMoveResetTest(
 		t,
 		metric.ValueObserverInstrumentKind,
-		func(desc *metric.Descriptor) export.Aggregator {
+		func(desc *metric.Descriptor) metric.Aggregator {
 			return &New(1)[0]
 		},
 	)
diff --git a/sdk/metric/aggregator/minmaxsumcount/mmsc.go b/sdk/metric/aggregator/minmaxsumcount/mmsc.go
index e21fd75ab73..9c886e9af1f 100644
--- a/sdk/metric/aggregator/minmaxsumcount/mmsc.go
+++ b/sdk/metric/aggregator/minmaxsumcount/mmsc.go
@@ -19,9 +19,8 @@ import (
 	"sync"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 )
 
@@ -42,7 +41,7 @@ type (
 	}
 )
 
-var _ export.Aggregator = &Aggregator{}
+var _ metric.Aggregator = &Aggregator{}
 var _ aggregation.MinMaxSumCount = &Aggregator{}
 
 // New returns a new aggregator for computing the min, max, sum, and
@@ -103,7 +102,7 @@ func (c *Aggregator) Max() (number.Number, error) {
 
 // SynchronizedMove saves the current state into oa and resets the current state to
 // the empty set.
-func (c *Aggregator) SynchronizedMove(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) SynchronizedMove(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 
 	if oa != nil && o == nil {
@@ -146,7 +145,7 @@ func (c *Aggregator) Update(_ context.Context, number number.Number, desc *metri
 }
 
 // Merge combines two data sets into one.
-func (c *Aggregator) Merge(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) Merge(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 	if o == nil {
 		return aggregator.NewInconsistentAggregatorError(c, oa)
diff --git a/sdk/metric/aggregator/minmaxsumcount/mmsc_test.go b/sdk/metric/aggregator/minmaxsumcount/mmsc_test.go
index 085c7a546d2..cb8448b6c3b 100644
--- a/sdk/metric/aggregator/minmaxsumcount/mmsc_test.go
+++ b/sdk/metric/aggregator/minmaxsumcount/mmsc_test.go
@@ -23,9 +23,8 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/aggregatortest"
 )
 
@@ -241,7 +240,7 @@ func TestSynchronizedMoveReset(t *testing.T) {
 	aggregatortest.SynchronizedMoveResetTest(
 		t,
 		metric.ValueRecorderInstrumentKind,
-		func(desc *metric.Descriptor) export.Aggregator {
+		func(desc *metric.Descriptor) metric.Aggregator {
 			return &New(1, desc)[0]
 		},
 	)
diff --git a/sdk/metric/aggregator/sum/sum.go b/sdk/metric/aggregator/sum/sum.go
index fc96ddb4cba..1264cabef8f 100644
--- a/sdk/metric/aggregator/sum/sum.go
+++ b/sdk/metric/aggregator/sum/sum.go
@@ -18,9 +18,9 @@ import (
 	"context"
 
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator"
 )
 
@@ -31,7 +31,7 @@ type Aggregator struct {
 	value number.Number
 }
 
-var _ export.Aggregator = &Aggregator{}
+var _ metric.Aggregator = &Aggregator{}
 var _ export.Subtractor = &Aggregator{}
 var _ aggregation.Sum = &Aggregator{}
 
@@ -60,7 +60,7 @@ func (c *Aggregator) Sum() (number.Number, error) {
 
 // SynchronizedMove atomically saves the current value into oa and resets the
 // current sum to zero.
-func (c *Aggregator) SynchronizedMove(oa export.Aggregator, _ *metric.Descriptor) error {
+func (c *Aggregator) SynchronizedMove(oa metric.Aggregator, _ *metric.Descriptor) error {
 	if oa == nil {
 		c.value.SetRawAtomic(0)
 		return nil
@@ -80,7 +80,7 @@ func (c *Aggregator) Update(_ context.Context, num number.Number, desc *metric.D
 }
 
 // Merge combines two counters by adding their sums.
-func (c *Aggregator) Merge(oa export.Aggregator, desc *metric.Descriptor) error {
+func (c *Aggregator) Merge(oa metric.Aggregator, desc *metric.Descriptor) error {
 	o, _ := oa.(*Aggregator)
 	if o == nil {
 		return aggregator.NewInconsistentAggregatorError(c, oa)
@@ -89,7 +89,7 @@ func (c *Aggregator) Merge(oa export.Aggregator, desc *metric.Descriptor) error
 	return nil
 }
 
-func (c *Aggregator) Subtract(opAgg, resAgg export.Aggregator, descriptor *metric.Descriptor) error {
+func (c *Aggregator) Subtract(opAgg, resAgg metric.Aggregator, descriptor *metric.Descriptor) error {
 	op, _ := opAgg.(*Aggregator)
 	if op == nil {
 		return aggregator.NewInconsistentAggregatorError(c, opAgg)
diff --git a/sdk/metric/aggregator/sum/sum_test.go b/sdk/metric/aggregator/sum/sum_test.go
index e63d2f9d690..10beaba63e6 100644
--- a/sdk/metric/aggregator/sum/sum_test.go
+++ b/sdk/metric/aggregator/sum/sum_test.go
@@ -24,7 +24,6 @@ import (
 	ottest "go.opentelemetry.io/otel/internal/internaltest"
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/aggregatortest"
 )
 
@@ -147,7 +146,7 @@ func TestSynchronizedMoveReset(t *testing.T) {
 	aggregatortest.SynchronizedMoveResetTest(
 		t,
 		metric.SumObserverInstrumentKind,
-		func(desc *metric.Descriptor) export.Aggregator {
+		func(desc *metric.Descriptor) metric.Aggregator {
 			return &New(1)[0]
 		},
 	)
diff --git a/sdk/metric/benchmark_test.go b/sdk/metric/benchmark_test.go
index 576d5c546a9..db5f6902dc7 100644
--- a/sdk/metric/benchmark_test.go
+++ b/sdk/metric/benchmark_test.go
@@ -32,7 +32,7 @@ type benchFixture struct {
 	meter       metric.Meter
 	accumulator *sdk.Accumulator
 	B           *testing.B
-	export.AggregatorSelector
+	metric.AggregatorSelector
 }
 
 func newFixture(b *testing.B) *benchFixture {
diff --git a/sdk/metric/controller/basic/controller_test.go b/sdk/metric/controller/basic/controller_test.go
index a1b3a7640b5..9fbaabf6e80 100644
--- a/sdk/metric/controller/basic/controller_test.go
+++ b/sdk/metric/controller/basic/controller_test.go
@@ -24,8 +24,8 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	controller "go.opentelemetry.io/otel/sdk/metric/controller/basic"
 	"go.opentelemetry.io/otel/sdk/metric/controller/controllertest"
 	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
diff --git a/sdk/metric/controller/basic/push_test.go b/sdk/metric/controller/basic/push_test.go
index 4add5f3f523..b3bf033c4ed 100644
--- a/sdk/metric/controller/basic/push_test.go
+++ b/sdk/metric/controller/basic/push_test.go
@@ -28,8 +28,8 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	controller "go.opentelemetry.io/otel/sdk/metric/controller/basic"
 	"go.opentelemetry.io/otel/sdk/metric/controller/controllertest"
 	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
diff --git a/sdk/metric/correct_test.go b/sdk/metric/correct_test.go
index 3cc6ef22596..0b62bd42b0d 100644
--- a/sdk/metric/correct_test.go
+++ b/sdk/metric/correct_test.go
@@ -26,9 +26,9 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	metricsdk "go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/metric/processor/processortest"
 	"go.opentelemetry.io/otel/sdk/resource"
@@ -80,11 +80,11 @@ type correctnessProcessor struct {
 }
 
 type testSelector struct {
-	selector    export.AggregatorSelector
+	selector    metric.AggregatorSelector
 	newAggCount int
 }
 
-func (ts *testSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...*export.Aggregator) {
+func (ts *testSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...*metric.Aggregator) {
 	ts.newAggCount += len(aggPtrs)
 	processortest.AggregatorSelector().AggregatorFor(desc, aggPtrs...)
 }
diff --git a/sdk/metric/processor/basic/basic.go b/sdk/metric/processor/basic/basic.go
index 2e2a7c5df41..ce7359049ca 100644
--- a/sdk/metric/processor/basic/basic.go
+++ b/sdk/metric/processor/basic/basic.go
@@ -22,15 +22,15 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
 type (
 	Processor struct {
 		export.ExportKindSelector
-		export.AggregatorSelector
+		metric.AggregatorSelector
 
 		state
 	}
@@ -79,17 +79,17 @@ type (
 		// (if !currentOwned) or it refers to an Aggregator
 		// owned by the processor used to accumulate multiple
 		// values in a single collection round.
-		current export.Aggregator
+		current metric.Aggregator
 
 		// delta, if non-nil, refers to an Aggregator owned by
 		// the processor used to compute deltas between
 		// precomputed sums.
-		delta export.Aggregator
+		delta metric.Aggregator
 
 		// cumulative, if non-nil, refers to an Aggregator owned
 		// by the processor used to store the last cumulative
 		// value.
-		cumulative export.Aggregator
+		cumulative metric.Aggregator
 	}
 
 	state struct {
@@ -127,7 +127,7 @@ var ErrInvalidExportKind = fmt.Errorf("invalid export kind")
 // is consulted to determine the kind(s) of exporter that will consume
 // data, so that this Processor can prepare to compute Delta or
 // Cumulative Aggregations as needed.
-func New(aselector export.AggregatorSelector, eselector export.ExportKindSelector, opts ...Option) *Processor {
+func New(aselector metric.AggregatorSelector, eselector export.ExportKindSelector, opts ...Option) *Processor {
 	now := time.Now()
 	p := &Processor{
 		AggregatorSelector: aselector,
diff --git a/sdk/metric/processor/basic/basic_test.go b/sdk/metric/processor/basic/basic_test.go
index 11b59717ea5..5b578eb7604 100644
--- a/sdk/metric/processor/basic/basic_test.go
+++ b/sdk/metric/processor/basic/basic_test.go
@@ -26,9 +26,9 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/export/metric/metrictest"
 	sdk "go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
@@ -103,9 +103,9 @@ func asNumber(nkind number.Kind, value int64) number.Number {
 	return number.NewFloat64Number(float64(value))
 }
 
-func updateFor(t *testing.T, desc *metric.Descriptor, selector export.AggregatorSelector, res *resource.Resource, value int64, labs ...label.KeyValue) export.Accumulation {
+func updateFor(t *testing.T, desc *metric.Descriptor, selector metric.AggregatorSelector, res *resource.Resource, value int64, labs ...label.KeyValue) export.Accumulation {
 	ls := label.NewSet(labs...)
-	var agg export.Aggregator
+	var agg metric.Aggregator
 	selector.AggregatorFor(desc, &agg)
 	require.NoError(t, agg.Update(context.Background(), asNumber(desc.NumberKind(), value), desc))
 
@@ -155,7 +155,7 @@ func testProcessor(
 
 			err := processor.FinishCollection()
 			if err == aggregation.ErrNoSubtraction {
-				var subr export.Aggregator
+				var subr metric.Aggregator
 				selector.AggregatorFor(&desc1, &subr)
 				_, canSub := subr.(export.Subtractor)
 
diff --git a/sdk/metric/processor/processortest/test.go b/sdk/metric/processor/processortest/test.go
index 9b767291b58..89a913bc1bd 100644
--- a/sdk/metric/processor/processortest/test.go
+++ b/sdk/metric/processor/processortest/test.go
@@ -23,9 +23,9 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/exact"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
@@ -49,7 +49,7 @@ type (
 	mapValue struct {
 		labels     *label.Set
 		resource   *resource.Resource
-		aggregator export.Aggregator
+		aggregator metric.Aggregator
 	}
 
 	// Output implements export.CheckpointSet.
@@ -74,7 +74,7 @@ type (
 	// Processor is a testing implementation of export.Processor that
 	// assembles its results as a map[string]float64.
 	Processor struct {
-		export.AggregatorSelector
+		metric.AggregatorSelector
 		output *Output
 	}
 
@@ -101,7 +101,7 @@ type (
 //
 // Where in the example A=1,B=2 is the encoded labels and R=V is the
 // encoded resource value.
-func NewProcessor(selector export.AggregatorSelector, encoder label.Encoder) *Processor {
+func NewProcessor(selector metric.AggregatorSelector, encoder label.Encoder) *Processor {
 	return &Processor{
 		AggregatorSelector: selector,
 		output:             NewOutput(encoder),
@@ -156,12 +156,12 @@ func (c *testCheckpointer) CheckpointSet() export.CheckpointSet {
 // AggregatorSelector returns a policy that is consistent with the
 // test descriptors above.  I.e., it returns sum.New() for counter
 // instruments and lastvalue.New() for lastValue instruments.
-func AggregatorSelector() export.AggregatorSelector {
+func AggregatorSelector() metric.AggregatorSelector {
 	return testAggregatorSelector{}
 }
 
 // AggregatorFor implements export.AggregatorSelector.
-func (testAggregatorSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...*export.Aggregator) {
+func (testAggregatorSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...*metric.Aggregator) {
 
 	switch {
 	case strings.HasSuffix(desc.Name(), ".disabled"):
@@ -237,7 +237,7 @@ func (o *Output) AddRecord(rec export.Record) error {
 		resource: rec.Resource().Equivalent(),
 	}
 	if _, ok := o.m[key]; !ok {
-		var agg export.Aggregator
+		var agg metric.Aggregator
 		testAggregatorSelector{}.AggregatorFor(rec.Descriptor(), &agg)
 		o.m[key] = mapValue{
 			aggregator: agg,
@@ -245,7 +245,7 @@ func (o *Output) AddRecord(rec export.Record) error {
 			resource:   rec.Resource(),
 		}
 	}
-	return o.m[key].aggregator.Merge(rec.Aggregation().(export.Aggregator), rec.Descriptor())
+	return o.m[key].aggregator.Merge(rec.Aggregation().(metric.Aggregator), rec.Descriptor())
 }
 
 // Map returns the calculated values for test validation from a set of
diff --git a/sdk/metric/sdk.go b/sdk/metric/sdk.go
index 14b381c3384..9ae8d77735a 100644
--- a/sdk/metric/sdk.go
+++ b/sdk/metric/sdk.go
@@ -118,8 +118,8 @@ type (
 		// current implements the actual RecordOne() API,
 		// depending on the type of aggregation.  If nil, the
 		// metric was disabled by the exporter.
-		current    export.Aggregator
-		checkpoint export.Aggregator
+		current    metric.Aggregator
+		checkpoint metric.Aggregator
 	}
 
 	instrument struct {
@@ -137,7 +137,7 @@ type (
 	labeledRecorder struct {
 		observedEpoch int64
 		labels        *label.Set
-		observed      export.Aggregator
+		observed      metric.Aggregator
 	}
 )
 
@@ -179,7 +179,7 @@ func (a *asyncInstrument) observe(num number.Number, labels *label.Set) {
 	}
 }
 
-func (a *asyncInstrument) getRecorder(labels *label.Set) export.Aggregator {
+func (a *asyncInstrument) getRecorder(labels *label.Set) metric.Aggregator {
 	lrec, ok := a.recorders[labels.Equivalent()]
 	if ok {
 		// Note: SynchronizedMove(nil) can't return an error
@@ -188,7 +188,7 @@ func (a *asyncInstrument) getRecorder(labels *label.Set) export.Aggregator {
 		a.recorders[labels.Equivalent()] = lrec
 		return lrec.observed
 	}
-	var rec export.Aggregator
+	var rec metric.Aggregator
 	a.meter.processor.AggregatorFor(&a.descriptor, &rec)
 	if a.recorders == nil {
 		a.recorders = make(map[label.Distinct]*labeledRecorder)
diff --git a/sdk/metric/selector/simple/simple.go b/sdk/metric/selector/simple/simple.go
index bb5760994ac..6ffef0a9187 100644
--- a/sdk/metric/selector/simple/simple.go
+++ b/sdk/metric/selector/simple/simple.go
@@ -16,7 +16,6 @@ package simple // import "go.opentelemetry.io/otel/sdk/metric/selector/simple"
 
 import (
 	"go.opentelemetry.io/otel/metric"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/exact"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
@@ -33,9 +32,9 @@ type (
 )
 
 var (
-	_ export.AggregatorSelector = selectorInexpensive{}
-	_ export.AggregatorSelector = selectorExact{}
-	_ export.AggregatorSelector = selectorHistogram{}
+	_ metric.AggregatorSelector = selectorInexpensive{}
+	_ metric.AggregatorSelector = selectorExact{}
+	_ metric.AggregatorSelector = selectorHistogram{}
 )
 
 // NewWithInexpensiveDistribution returns a simple aggregator selector
@@ -43,7 +42,7 @@ var (
 // instruments.  This selector is faster and uses less memory than the
 // others in this package because minmaxsumcount aggregators maintain
 // the least information about the distribution among these choices.
-func NewWithInexpensiveDistribution() export.AggregatorSelector {
+func NewWithInexpensiveDistribution() metric.AggregatorSelector {
 	return selectorInexpensive{}
 }
 
@@ -52,32 +51,32 @@ func NewWithInexpensiveDistribution() export.AggregatorSelector {
 // selector uses more memory than the others in this package because
 // exact aggregators maintain the most information about the
 // distribution among these choices.
-func NewWithExactDistribution() export.AggregatorSelector {
+func NewWithExactDistribution() metric.AggregatorSelector {
 	return selectorExact{}
 }
 
 // NewWithHistogramDistribution returns a simple aggregator selector
 // that uses histogram aggregators for `ValueRecorder` instruments.
 // This selector is a good default choice for most metric exporters.
-func NewWithHistogramDistribution(options ...histogram.Option) export.AggregatorSelector {
+func NewWithHistogramDistribution(options ...histogram.Option) metric.AggregatorSelector {
 	return selectorHistogram{options: options}
 }
 
-func sumAggs(aggPtrs []*export.Aggregator) {
+func sumAggs(aggPtrs []*metric.Aggregator) {
 	aggs := sum.New(len(aggPtrs))
 	for i := range aggPtrs {
 		*aggPtrs[i] = &aggs[i]
 	}
 }
 
-func lastValueAggs(aggPtrs []*export.Aggregator) {
+func lastValueAggs(aggPtrs []*metric.Aggregator) {
 	aggs := lastvalue.New(len(aggPtrs))
 	for i := range aggPtrs {
 		*aggPtrs[i] = &aggs[i]
 	}
 }
 
-func (selectorInexpensive) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*export.Aggregator) {
+func (selectorInexpensive) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*metric.Aggregator) {
 	switch descriptor.InstrumentKind() {
 	case metric.ValueObserverInstrumentKind:
 		lastValueAggs(aggPtrs)
@@ -91,7 +90,7 @@ func (selectorInexpensive) AggregatorFor(descriptor *metric.Descriptor, aggPtrs
 	}
 }
 
-func (selectorExact) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*export.Aggregator) {
+func (selectorExact) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*metric.Aggregator) {
 	switch descriptor.InstrumentKind() {
 	case metric.ValueObserverInstrumentKind:
 		lastValueAggs(aggPtrs)
@@ -105,7 +104,7 @@ func (selectorExact) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*ex
 	}
 }
 
-func (s selectorHistogram) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*export.Aggregator) {
+func (s selectorHistogram) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*metric.Aggregator) {
 	switch descriptor.InstrumentKind() {
 	case metric.ValueObserverInstrumentKind:
 		lastValueAggs(aggPtrs)
diff --git a/sdk/metric/selector/simple/simple_test.go b/sdk/metric/selector/simple/simple_test.go
index cd7dab46357..607722fd2ab 100644
--- a/sdk/metric/selector/simple/simple_test.go
+++ b/sdk/metric/selector/simple/simple_test.go
@@ -21,7 +21,6 @@ import (
 
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/metric/number"
-	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/exact"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
@@ -39,13 +38,13 @@ var (
 	testValueObserverDesc     = metric.NewDescriptor("valueobserver", metric.ValueObserverInstrumentKind, number.Int64Kind)
 )
 
-func oneAgg(sel export.AggregatorSelector, desc *metric.Descriptor) export.Aggregator {
-	var agg export.Aggregator
+func oneAgg(sel metric.AggregatorSelector, desc *metric.Descriptor) metric.Aggregator {
+	var agg metric.Aggregator
 	sel.AggregatorFor(desc, &agg)
 	return agg
 }
 
-func testFixedSelectors(t *testing.T, sel export.AggregatorSelector) {
+func testFixedSelectors(t *testing.T, sel metric.AggregatorSelector) {
 	require.IsType(t, (*lastvalue.Aggregator)(nil), oneAgg(sel, &testValueObserverDesc))
 	require.IsType(t, (*sum.Aggregator)(nil), oneAgg(sel, &testCounterDesc))
 	require.IsType(t, (*sum.Aggregator)(nil), oneAgg(sel, &testUpDownCounterDesc))
diff --git a/sdk/metric/stress_test.go b/sdk/metric/stress_test.go
index 4878435bde3..94f330807b4 100644
--- a/sdk/metric/stress_test.go
+++ b/sdk/metric/stress_test.go
@@ -33,9 +33,9 @@ import (
 
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/metric/aggregation"
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/processor/processortest"
 )
 
@@ -58,7 +58,7 @@ type (
 		impl     testImpl
 		T        *testing.T
 
-		export.AggregatorSelector
+		metric.AggregatorSelector
 
 		lock  sync.Mutex
 		lused map[string]bool

From fec26e5714665bf16244eb624b76d5e55deedc9a Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 10:32:24 +1100
Subject: [PATCH 2/9] add View type and meter.RegisterView method to public
 Metric API

---
 internal/global/meter.go         |  5 ++
 metric/metric.go                 | 12 +++++
 metric/metric_sdkapi.go          |  3 ++
 metric/metric_test.go            | 15 ++++++
 metric/metric_view.go            | 85 ++++++++++++++++++++++++++++++++
 metric/registry/registry.go      |  5 ++
 metric/viewlabelconfig_string.go | 25 ++++++++++
 oteltest/meter.go                |  4 ++
 sdk/metric/sdk.go                |  4 ++
 9 files changed, 158 insertions(+)
 create mode 100644 metric/metric_view.go
 create mode 100644 metric/viewlabelconfig_string.go

diff --git a/internal/global/meter.go b/internal/global/meter.go
index 8b288df780f..ca2bde6e0cd 100644
--- a/internal/global/meter.go
+++ b/internal/global/meter.go
@@ -185,6 +185,11 @@ func (m *meterImpl) setDelegate(name, version string, provider metric.MeterProvi
 	m.asyncInsts = nil
 }
 
+// RegisterView is a no-op here.
+func (m *meterImpl) RegisterView(metric.View) {
+	// Should we panic here?
+}
+
 func (m *meterImpl) NewSyncInstrument(desc metric.Descriptor) (metric.SyncImpl, error) {
 	m.lock.Lock()
 	defer m.lock.Unlock()
diff --git a/metric/metric.go b/metric/metric.go
index 0b988abba88..979d8c36bed 100644
--- a/metric/metric.go
+++ b/metric/metric.go
@@ -41,6 +41,13 @@ type Meter struct {
 	name, version string
 }
 
+// RegisterView registers a view for a synchronous instrument.
+func (m Meter) RegisterView(v View) {
+	if m.impl != nil {
+		m.impl.RegisterView(v)
+	}
+}
+
 // RecordBatch atomically records a batch of measurements.
 func (m Meter) RecordBatch(ctx context.Context, ls []label.KeyValue, ms ...Measurement) {
 	if m.impl == nil {
@@ -328,6 +335,11 @@ func Must(meter Meter) MeterMust {
 	return MeterMust{meter: meter}
 }
 
+// RegisterView calls `Meter.RegisterView`
+func (mm MeterMust) RegisterView(v View) {
+	mm.meter.RegisterView(v)
+}
+
 // NewInt64Counter calls `Meter.NewInt64Counter` and returns the
 // instrument, panicking if it encounters an error.
 func (mm MeterMust) NewInt64Counter(name string, cos ...InstrumentOption) Int64Counter {
diff --git a/metric/metric_sdkapi.go b/metric/metric_sdkapi.go
index 77d6adb173b..c87eb415723 100644
--- a/metric/metric_sdkapi.go
+++ b/metric/metric_sdkapi.go
@@ -24,6 +24,9 @@ import (
 // MeterImpl is the interface an SDK must implement to supply a Meter
 // implementation.
 type MeterImpl interface {
+	// RegisterView registers a view for a synchronous instrument.
+	RegisterView(v View)
+
 	// RecordBatch atomically records a batch of measurements.
 	RecordBatch(ctx context.Context, labels []label.KeyValue, measurement ...Measurement)
 
diff --git a/metric/metric_test.go b/metric/metric_test.go
index 3250f0e1588..774234a4b6e 100644
--- a/metric/metric_test.go
+++ b/metric/metric_test.go
@@ -206,6 +206,18 @@ func TestOptions(t *testing.T) {
 	}
 }
 
+func TestViewPanic(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("The code did not panic")
+		}
+	}()
+
+	_, meter := oteltest.NewMeter()
+	c := Must(meter).NewFloat64Counter("test.counter.float")
+	meter.RegisterView(metric.NewView(c.SyncImpl(), metric.DropAll, nil, nil))
+}
+
 func TestCounter(t *testing.T) {
 	// N.B. the API does not check for negative
 	// values, that's the SDK's responsibility.
@@ -435,6 +447,9 @@ type testWrappedMeter struct {
 
 var _ metric.MeterImpl = testWrappedMeter{}
 
+func (testWrappedMeter) RegisterView(metric.View) {
+}
+
 func (testWrappedMeter) RecordBatch(context.Context, []label.KeyValue, ...metric.Measurement) {
 }
 
diff --git a/metric/metric_view.go b/metric/metric_view.go
new file mode 100644
index 00000000000..7c8e2923817
--- /dev/null
+++ b/metric/metric_view.go
@@ -0,0 +1,85 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metric // import "go.opentelemetry.io/otel/metric"
+
+import (
+	"go.opentelemetry.io/otel/label"
+)
+
+//go:generate stringer -type=ViewLabelConfig
+
+// ViewLabelConfig is the option to control how to track the set of labels
+// for a given view.
+// See available values for more details.
+type ViewLabelConfig uint8
+
+const (
+	// Drop all label keys, and aggregate all measurements from the metric
+	// instrument together regardless of their label sets.
+	//
+	// Note: the DropAll is the same as LabelKeys with empty keys.
+	DropAll ViewLabelConfig = iota
+
+	// Record all label keys. This is the default option without explicitly
+	// registering a view.
+	Ungroup
+
+	// Specify a set of label keys to track at view creation time, and drop
+	// other keys from the label sets of recorded measurements before
+	// aggregating.
+	//
+	// Note: some label values may be undefined if the measurements don't
+	// provide all label values.
+	LabelKeys
+)
+
+// View supports configuring non-default aggregation behaviors on the level
+// of an individual synchronous instrument.
+type View struct {
+	inst               SyncImpl
+	labelConfig        ViewLabelConfig
+	labelKeys          []label.Key
+	aggregatorSelector AggregatorSelector
+}
+
+// SyncImpl returns the associated synchronous instrument interface for a given view.
+func (v View) SyncImpl() SyncImpl {
+	return v.inst
+}
+
+// LabelConfig returns the label tracking option for a given view.
+func (v View) LabelConfig() ViewLabelConfig {
+	return v.labelConfig
+}
+
+// LabelKeys returns the pre-configured label keys for a given view.
+func (v View) LabelKeys() []label.Key {
+	return v.labelKeys
+}
+
+// AggregatorFactory returns the AggregatorFactory instance for a given view.
+func (v View) AggregatorFactory() AggregatorSelector {
+	return v.aggregatorSelector
+}
+
+// NewView returns a view object for the given parameters.
+func NewView(inst SyncImpl, labelConfig ViewLabelConfig, labelKeys []label.Key, selector AggregatorSelector) View {
+	return View{
+		inst:               inst,
+		labelConfig:        labelConfig,
+		labelKeys:          labelKeys,
+		aggregatorSelector: selector,
+	}
+}
diff --git a/metric/registry/registry.go b/metric/registry/registry.go
index f1d9819c319..830c6ac86bb 100644
--- a/metric/registry/registry.go
+++ b/metric/registry/registry.go
@@ -74,6 +74,11 @@ func NewUniqueInstrumentMeterImpl(impl metric.MeterImpl) metric.MeterImpl {
 	}
 }
 
+// RegisterView implements metric.MeterImpl.
+func (u *uniqueInstrumentMeterImpl) RegisterView(v metric.View) {
+	u.impl.RegisterView(v)
+}
+
 // RecordBatch implements metric.MeterImpl.
 func (u *uniqueInstrumentMeterImpl) RecordBatch(ctx context.Context, labels []label.KeyValue, ms ...metric.Measurement) {
 	u.impl.RecordBatch(ctx, labels, ms...)
diff --git a/metric/viewlabelconfig_string.go b/metric/viewlabelconfig_string.go
new file mode 100644
index 00000000000..660cc2a91cf
--- /dev/null
+++ b/metric/viewlabelconfig_string.go
@@ -0,0 +1,25 @@
+// Code generated by "stringer -type=ViewLabelConfig"; DO NOT EDIT.
+
+package metric
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[DropAll-0]
+	_ = x[Ungroup-1]
+	_ = x[LabelKeys-2]
+}
+
+const _ViewLabelConfig_name = "DropAllUngroupLabelKeys"
+
+var _ViewLabelConfig_index = [...]uint8{0, 7, 14, 23}
+
+func (i ViewLabelConfig) String() string {
+	if i >= ViewLabelConfig(len(_ViewLabelConfig_index)-1) {
+		return "ViewLabelConfig(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _ViewLabelConfig_name[_ViewLabelConfig_index[i]:_ViewLabelConfig_index[i+1]]
+}
diff --git a/oteltest/meter.go b/oteltest/meter.go
index d7899ce71a8..ede9a7da9a2 100644
--- a/oteltest/meter.go
+++ b/oteltest/meter.go
@@ -127,6 +127,10 @@ func NewMeter() (*MeterImpl, metric.Meter) {
 	return impl, p.Meter("mock")
 }
 
+func (m *MeterImpl) RegisterView(v metric.View) {
+	panic("me")
+}
+
 func (m *MeterImpl) NewSyncInstrument(descriptor metric.Descriptor) (metric.SyncImpl, error) {
 	m.lock.Lock()
 	defer m.lock.Unlock()
diff --git a/sdk/metric/sdk.go b/sdk/metric/sdk.go
index 9ae8d77735a..82e5050ba9e 100644
--- a/sdk/metric/sdk.go
+++ b/sdk/metric/sdk.go
@@ -309,6 +309,10 @@ func NewAccumulator(processor export.Processor, resource *resource.Resource) *Ac
 	}
 }
 
+func (m *Accumulator) RegisterView(v metric.View) {
+	panic("me")
+}
+
 // NewSyncInstrument implements metric.MetricImpl.
 func (m *Accumulator) NewSyncInstrument(descriptor metric.Descriptor) (metric.SyncImpl, error) {
 	return &syncInstrument{

From a3dfcd3812ed3019c2650d2c493d249558f9f191 Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 10:32:55 +1100
Subject: [PATCH 3/9] support labels with values unset for View API

---
 label/key.go        | 12 ++++++++++++
 label/kv.go         |  5 +++++
 label/kv_test.go    |  8 ++++++++
 label/value.go      |  7 +++++++
 label/value_test.go |  6 ++++++
 5 files changed, 38 insertions(+)

diff --git a/label/key.go b/label/key.go
index 732fa2523a7..0a94093f2a9 100644
--- a/label/key.go
+++ b/label/key.go
@@ -18,6 +18,18 @@ package label // import "go.opentelemetry.io/otel/label"
 // allowed character set in the key depends on the use of the key.
 type Key string
 
+// Empty creates a KeyValue instance with value unset.
+//
+// Consider using a convenience function provided by the
+// api/key package -
+// key.Int64(name, value).
+func (k Key) Empty() KeyValue {
+	return KeyValue{
+		Key:   k,
+		Value: EmptyValue(),
+	}
+}
+
 // Bool creates a KeyValue instance with a BOOL Value.
 //
 // If creating both key and a bool value at the same time, then
diff --git a/label/kv.go b/label/kv.go
index 0520f4f41a8..43cb85989bf 100644
--- a/label/kv.go
+++ b/label/kv.go
@@ -26,6 +26,11 @@ type KeyValue struct {
 	Value Value
 }
 
+// Empty creates an empty key-value pair with a passed name.
+func Empty(k string) KeyValue {
+	return Key(k).Empty()
+}
+
 // Bool creates a new key-value pair with a passed name and a bool
 // value.
 func Bool(k string, v bool) KeyValue {
diff --git a/label/kv_test.go b/label/kv_test.go
index 068d2932381..f0aa3617989 100644
--- a/label/kv_test.go
+++ b/label/kv_test.go
@@ -29,6 +29,14 @@ func TestKeyValueConstructors(t *testing.T) {
 		actual   label.KeyValue
 		expected label.KeyValue
 	}{
+		{
+			name:   "Empty",
+			actual: label.Empty("k1"),
+			expected: label.KeyValue{
+				Key:   "k1",
+				Value: label.EmptyValue(),
+			},
+		},
 		{
 			name:   "Bool",
 			actual: label.Bool("k1", true),
diff --git a/label/value.go b/label/value.go
index 6cc0bee80c9..571714a53b5 100644
--- a/label/value.go
+++ b/label/value.go
@@ -64,6 +64,13 @@ const (
 	ARRAY
 )
 
+// EmptyValue creates a Value with no value set.
+func EmptyValue() Value {
+	return Value{
+		vtype: INVALID,
+	}
+}
+
 // BoolValue creates a BOOL Value.
 func BoolValue(v bool) Value {
 	return Value{
diff --git a/label/value_test.go b/label/value_test.go
index 7842fceef08..96a52df36ab 100644
--- a/label/value_test.go
+++ b/label/value_test.go
@@ -33,6 +33,12 @@ func TestValue(t *testing.T) {
 		wantType  label.Type
 		wantValue interface{}
 	}{
+		{
+			name:      "Key.Empty() correctly returns key's internal empty value",
+			value:     k.Empty().Value,
+			wantType:  label.INVALID,
+			wantValue: nil,
+		},
 		{
 			name:      "Key.Bool() correctly returns keys's internal bool value",
 			value:     k.Bool(true).Value,

From 6eea9e94960b892064722f423d38215cf6de1373 Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 10:33:16 +1100
Subject: [PATCH 4/9] add view selector that takes precedence over the default
 AggregatorSelector in metrics processing/exporting

---
 sdk/export/metric/metric.go              | 19 +++++--
 sdk/metric/processor/basic/basic.go      | 20 +++++--
 sdk/metric/processor/basic/basic_test.go | 67 ++++++++++++++----------
 sdk/metric/processor/reducer/reducer.go  |  1 +
 sdk/metric/sdk.go                        |  4 +-
 5 files changed, 74 insertions(+), 37 deletions(-)

diff --git a/sdk/export/metric/metric.go b/sdk/export/metric/metric.go
index b1f01a6ec93..3b762a04322 100644
--- a/sdk/export/metric/metric.go
+++ b/sdk/export/metric/metric.go
@@ -188,7 +188,8 @@ type Metadata struct {
 // and label set, as prepared by an Accumulator for the Processor.
 type Accumulation struct {
 	Metadata
-	aggregator metric.Aggregator
+	aggregator   metric.Aggregator
+	viewSelector metric.AggregatorSelector
 }
 
 // Record contains the exported data for a single metric instrument
@@ -219,16 +220,17 @@ func (m Metadata) Resource() *resource.Resource {
 
 // NewAccumulation allows Accumulator implementations to construct new
 // Accumulations to send to Processors. The Descriptor, Labels, Resource,
-// and Aggregator represent aggregate metric events received over a single
-// collection period.
-func NewAccumulation(descriptor *metric.Descriptor, labels *label.Set, resource *resource.Resource, aggregator metric.Aggregator) Accumulation {
+// Aggregator and AggregatorSelector represent aggregate metric events
+// received over a single collection period.
+func NewAccumulation(descriptor *metric.Descriptor, labels *label.Set, resource *resource.Resource, aggregator metric.Aggregator, viewSelector metric.AggregatorSelector) Accumulation {
 	return Accumulation{
 		Metadata: Metadata{
 			descriptor: descriptor,
 			labels:     labels,
 			resource:   resource,
 		},
-		aggregator: aggregator,
+		aggregator:   aggregator,
+		viewSelector: viewSelector,
 	}
 }
 
@@ -238,6 +240,13 @@ func (r Accumulation) Aggregator() metric.Aggregator {
 	return r.aggregator
 }
 
+// ViewAggregatorSelector returns the aggregator selector object for an
+// instrument associated with a view. This could be nil indicating
+// the default AggregaotSelector should be used.
+func (r Accumulation) ViewAggregatorSelector() metric.AggregatorSelector {
+	return r.viewSelector
+}
+
 // NewRecord allows Processor implementations to construct export
 // records.  The Descriptor, Labels, and Aggregator represent
 // aggregate metric events received over a single collection period.
diff --git a/sdk/metric/processor/basic/basic.go b/sdk/metric/processor/basic/basic.go
index ce7359049ca..0d45ed8e3ac 100644
--- a/sdk/metric/processor/basic/basic.go
+++ b/sdk/metric/processor/basic/basic.go
@@ -144,6 +144,20 @@ func New(aselector metric.AggregatorSelector, eselector export.ExportKindSelecto
 	return p
 }
 
+// allocateAggregator allocates a variable number of aggregators of a kind
+// suitable for the `descriptor`.
+//
+// If `viewSelector` is not `nil`, it would be used to initialize the
+// aggregators. Otherwise, the AggregatorSelector associated with the
+// `Processor` would be .
+func (b *Processor) allocAggregator(descriptor *metric.Descriptor, viewSelector metric.AggregatorSelector, aggregator ...*metric.Aggregator) {
+	if viewSelector != nil {
+		viewSelector.AggregatorFor(descriptor, aggregator...)
+	} else {
+		b.AggregatorFor(descriptor, aggregator...)
+	}
+}
+
 // Process implements export.Processor.
 func (b *Processor) Process(accum export.Accumulation) error {
 	if b.startedCollection != b.finishedCollection+1 {
@@ -172,11 +186,11 @@ func (b *Processor) Process(accum export.Accumulation) error {
 		if stateful {
 			if desc.InstrumentKind().PrecomputedSum() {
 				// If we know we need to compute deltas, allocate two aggregators.
-				b.AggregatorFor(desc, &newValue.cumulative, &newValue.delta)
+				b.allocAggregator(desc, accum.ViewAggregatorSelector(), &newValue.cumulative, &newValue.delta)
 			} else {
 				// In this case we are certain not to need a delta, only allocate
 				// a cumulative aggregator.
-				b.AggregatorFor(desc, &newValue.cumulative)
+				b.allocAggregator(desc, accum.ViewAggregatorSelector(), &newValue.cumulative)
 			}
 		}
 		b.state.values[key] = newValue
@@ -233,7 +247,7 @@ func (b *Processor) Process(accum export.Accumulation) error {
 	// before merging below.
 	if !value.currentOwned {
 		tmp := value.current
-		b.AggregatorSelector.AggregatorFor(desc, &value.current)
+		b.allocAggregator(desc, accum.ViewAggregatorSelector(), &value.current)
 		value.currentOwned = true
 		if err := tmp.SynchronizedMove(value.current, desc); err != nil {
 			return err
diff --git a/sdk/metric/processor/basic/basic_test.go b/sdk/metric/processor/basic/basic_test.go
index 5b578eb7604..58f1f48e1ed 100644
--- a/sdk/metric/processor/basic/basic_test.go
+++ b/sdk/metric/processor/basic/basic_test.go
@@ -103,13 +103,18 @@ func asNumber(nkind number.Kind, value int64) number.Number {
 	return number.NewFloat64Number(float64(value))
 }
 
-func updateFor(t *testing.T, desc *metric.Descriptor, selector metric.AggregatorSelector, res *resource.Resource, value int64, labs ...label.KeyValue) export.Accumulation {
+func updateFor(t *testing.T, desc *metric.Descriptor, selector metric.AggregatorSelector, provideViewSelector bool, res *resource.Resource, value int64, labs ...label.KeyValue) export.Accumulation {
 	ls := label.NewSet(labs...)
 	var agg metric.Aggregator
 	selector.AggregatorFor(desc, &agg)
 	require.NoError(t, agg.Update(context.Background(), asNumber(desc.NumberKind(), value), desc))
 
-	return export.NewAccumulation(desc, &ls, res, agg)
+	var accSelector metric.AggregatorSelector
+	if provideViewSelector {
+		accSelector = selector
+	}
+
+	return export.NewAccumulation(desc, &ls, res, agg, accSelector)
 }
 
 func testProcessor(
@@ -127,8 +132,14 @@ func testProcessor(
 	labs1 := []label.KeyValue{label.String("L1", "V")}
 	labs2 := []label.KeyValue{label.String("L2", "V")}
 
-	testBody := func(t *testing.T, hasMemory bool, nAccum, nCheckpoint int) {
-		processor := basic.New(selector, export.ConstantExportKindSelector(ekind), basic.WithMemory(hasMemory))
+	testBody := func(t *testing.T, provideViewSelector, hasMemory bool, nAccum, nCheckpoint int) {
+		// testSelector would be nil given a view selector.
+		var testSelector metric.AggregatorSelector
+		if !provideViewSelector {
+			testSelector = selector
+		}
+
+		processor := basic.New(testSelector, export.ConstantExportKindSelector(ekind), basic.WithMemory(hasMemory))
 
 		instSuffix := fmt.Sprint(".", strings.ToLower(akind.String()))
 
@@ -149,8 +160,8 @@ func testProcessor(
 			processor.StartCollection()
 
 			for na := 0; na < nAccum; na++ {
-				_ = processor.Process(updateFor(t, &desc1, selector, res, input, labs1...))
-				_ = processor.Process(updateFor(t, &desc2, selector, res, input, labs2...))
+				_ = processor.Process(updateFor(t, &desc1, selector, provideViewSelector, res, input, labs1...))
+				_ = processor.Process(updateFor(t, &desc2, selector, provideViewSelector, res, input, labs2...))
 			}
 
 			err := processor.FinishCollection()
@@ -240,20 +251,22 @@ func testProcessor(
 		}
 	}
 
-	for _, hasMem := range []bool{false, true} {
-		t.Run(fmt.Sprintf("HasMemory=%v", hasMem), func(t *testing.T) {
-			// For 1 to 3 checkpoints:
-			for nAccum := 1; nAccum <= 3; nAccum++ {
-				t.Run(fmt.Sprintf("NumAccum=%d", nAccum), func(t *testing.T) {
-					// For 1 to 3 accumulators:
-					for nCheckpoint := 1; nCheckpoint <= 3; nCheckpoint++ {
-						t.Run(fmt.Sprintf("NumCkpt=%d", nCheckpoint), func(t *testing.T) {
-							testBody(t, hasMem, nAccum, nCheckpoint)
-						})
-					}
-				})
-			}
-		})
+	for _, provideAggrFactory := range []bool{false, true} {
+		for _, hasMem := range []bool{false, true} {
+			t.Run(fmt.Sprintf("HasMemory=%v", hasMem), func(t *testing.T) {
+				// For 1 to 3 checkpoints:
+				for nAccum := 1; nAccum <= 3; nAccum++ {
+					t.Run(fmt.Sprintf("NumAccum=%d", nAccum), func(t *testing.T) {
+						// For 1 to 3 accumulators:
+						for nCheckpoint := 1; nCheckpoint <= 3; nCheckpoint++ {
+							t.Run(fmt.Sprintf("NumCkpt=%d", nCheckpoint), func(t *testing.T) {
+								testBody(t, provideAggrFactory, hasMem, nAccum, nCheckpoint)
+							})
+						}
+					})
+				}
+			})
+		}
 	}
 }
 
@@ -297,7 +310,7 @@ func TestBasicInconsistent(t *testing.T) {
 	b = basic.New(processorTest.AggregatorSelector(), export.StatelessExportKindSelector())
 
 	desc := metric.NewDescriptor("inst", metric.CounterInstrumentKind, number.Int64Kind)
-	accum := export.NewAccumulation(&desc, label.EmptySet(), resource.Empty(), metrictest.NoopAggregator{})
+	accum := export.NewAccumulation(&desc, label.EmptySet(), resource.Empty(), metrictest.NoopAggregator{}, nil)
 	require.Equal(t, basic.ErrInconsistentState, b.Process(accum))
 
 	// Test invalid kind:
@@ -320,7 +333,7 @@ func TestBasicTimestamps(t *testing.T) {
 	afterNew := time.Now()
 
 	desc := metric.NewDescriptor("inst", metric.CounterInstrumentKind, number.Int64Kind)
-	accum := export.NewAccumulation(&desc, label.EmptySet(), resource.Empty(), metrictest.NoopAggregator{})
+	accum := export.NewAccumulation(&desc, label.EmptySet(), resource.Empty(), metrictest.NoopAggregator{}, nil)
 
 	b.StartCollection()
 	_ = b.Process(accum)
@@ -383,7 +396,7 @@ func TestStatefulNoMemoryCumulative(t *testing.T) {
 
 		// Add 10
 		processor.StartCollection()
-		_ = processor.Process(updateFor(t, &desc, selector, res, 10, label.String("A", "B")))
+		_ = processor.Process(updateFor(t, &desc, selector, false, res, 10, label.String("A", "B")))
 		require.NoError(t, processor.FinishCollection())
 
 		// Verify one element
@@ -417,7 +430,7 @@ func TestStatefulNoMemoryDelta(t *testing.T) {
 
 		// Add 10
 		processor.StartCollection()
-		_ = processor.Process(updateFor(t, &desc, selector, res, int64(i*10), label.String("A", "B")))
+		_ = processor.Process(updateFor(t, &desc, selector, false, res, int64(i*10), label.String("A", "B")))
 		require.NoError(t, processor.FinishCollection())
 
 		// Verify one element
@@ -445,9 +458,9 @@ func TestMultiObserverSum(t *testing.T) {
 		for i := 1; i < 3; i++ {
 			// Add i*10*3 times
 			processor.StartCollection()
-			_ = processor.Process(updateFor(t, &desc, selector, res, int64(i*10), label.String("A", "B")))
-			_ = processor.Process(updateFor(t, &desc, selector, res, int64(i*10), label.String("A", "B")))
-			_ = processor.Process(updateFor(t, &desc, selector, res, int64(i*10), label.String("A", "B")))
+			_ = processor.Process(updateFor(t, &desc, selector, false, res, int64(i*10), label.String("A", "B")))
+			_ = processor.Process(updateFor(t, &desc, selector, false, res, int64(i*10), label.String("A", "B")))
+			_ = processor.Process(updateFor(t, &desc, selector, false, res, int64(i*10), label.String("A", "B")))
 			require.NoError(t, processor.FinishCollection())
 
 			// Multiplier is 1 for deltas, otherwise i.
diff --git a/sdk/metric/processor/reducer/reducer.go b/sdk/metric/processor/reducer/reducer.go
index 91c4dae2d52..6a7b8ea5731 100644
--- a/sdk/metric/processor/reducer/reducer.go
+++ b/sdk/metric/processor/reducer/reducer.go
@@ -62,6 +62,7 @@ func (p *Processor) Process(accum export.Accumulation) error {
 			&reduced,
 			accum.Resource(),
 			accum.Aggregator(),
+			nil,
 		),
 	)
 }
diff --git a/sdk/metric/sdk.go b/sdk/metric/sdk.go
index 82e5050ba9e..d2cc369b8c8 100644
--- a/sdk/metric/sdk.go
+++ b/sdk/metric/sdk.go
@@ -437,7 +437,7 @@ func (m *Accumulator) checkpointRecord(r *record) int {
 		return 0
 	}
 
-	a := export.NewAccumulation(&r.inst.descriptor, r.labels, m.resource, r.checkpoint)
+	a := export.NewAccumulation(&r.inst.descriptor, r.labels, m.resource, r.checkpoint, nil)
 	err = m.processor.Process(a)
 	if err != nil {
 		otel.Handle(err)
@@ -455,7 +455,7 @@ func (m *Accumulator) checkpointAsync(a *asyncInstrument) int {
 		epochDiff := m.currentEpoch - lrec.observedEpoch
 		if epochDiff == 0 {
 			if lrec.observed != nil {
-				a := export.NewAccumulation(&a.descriptor, lrec.labels, m.resource, lrec.observed)
+				a := export.NewAccumulation(&a.descriptor, lrec.labels, m.resource, lrec.observed, nil)
 				err := m.processor.Process(a)
 				if err != nil {
 					otel.Handle(err)

From f70f95827efe8e6d49c143ac02c48626546e97f4 Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 10:33:40 +1100
Subject: [PATCH 5/9] support the Metrics View API

---
 sdk/metric/correct_test.go | 111 ++++++++++++++++++++
 sdk/metric/sdk.go          | 200 ++++++++++++++++++++++++++++++-------
 2 files changed, 273 insertions(+), 38 deletions(-)

diff --git a/sdk/metric/correct_test.go b/sdk/metric/correct_test.go
index 0b62bd42b0d..904b1259b28 100644
--- a/sdk/metric/correct_test.go
+++ b/sdk/metric/correct_test.go
@@ -30,6 +30,7 @@ import (
 	"go.opentelemetry.io/otel/metric/number"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	metricsdk "go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
 	"go.opentelemetry.io/otel/sdk/metric/processor/processortest"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
@@ -89,6 +90,16 @@ func (ts *testSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...*metri
 	processortest.AggregatorSelector().AggregatorFor(desc, aggPtrs...)
 }
 
+type testAlwaysLastValueAggregatorSelector struct {
+}
+
+func (t *testAlwaysLastValueAggregatorSelector) AggregatorFor(descriptor *metric.Descriptor, aggPtrs ...*metric.Aggregator) {
+	aggs := lastvalue.New(len(aggPtrs))
+	for i := range aggPtrs {
+		*aggPtrs[i] = &aggs[i]
+	}
+}
+
 func newSDK(t *testing.T) (metric.Meter, *metricsdk.Accumulator, *correctnessProcessor) {
 	testHandler.Reset()
 	processor := &correctnessProcessor{
@@ -174,6 +185,106 @@ func TestInputRangeValueRecorder(t *testing.T) {
 	require.Nil(t, err)
 }
 
+func TestViewDropAllLabels(t *testing.T) {
+	ctx := context.Background()
+	meter, sdk, processor := newSDK(t)
+
+	valuerecorder := Must(meter).NewFloat64ValueRecorder("name.exact")
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.DropAll, nil, nil))
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.LabelKeys, nil, nil))
+
+	valuerecorder.Record(ctx, 1.0, label.String("A", "a"))
+
+	checkpointed := sdk.Collect(ctx)
+	require.Equal(t, 1, checkpointed)
+
+	require.Equal(t, 1, len(processor.accumulations))
+	require.Equal(t, 0, processor.accumulations[0].Labels().Len())
+}
+
+func TestViewUngroupLabels(t *testing.T) {
+	ctx := context.Background()
+	meter, sdk, processor := newSDK(t)
+
+	valuerecorder := Must(meter).NewFloat64ValueRecorder("name.exact")
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.Ungroup, nil, nil))
+
+	valuerecorder.Record(ctx, 1.0, label.String("A", "a"))
+
+	checkpointed := sdk.Collect(ctx)
+	require.Equal(t, 1, checkpointed)
+
+	labels := processor.accumulations[0].Labels().ToSlice()
+	require.ElementsMatch(t, labels, []label.KeyValue{label.String("A", "a")})
+}
+
+func TestViewLabelKeys(t *testing.T) {
+	ctx := context.Background()
+	meter, sdk, processor := newSDK(t)
+
+	valuerecorder := Must(meter).NewFloat64ValueRecorder("name.exact")
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.LabelKeys, []label.Key{"A", "B"}, nil))
+
+	valuerecorder.Record(ctx, 1.0, label.String("A", "a"))
+
+	checkpointed := sdk.Collect(ctx)
+	require.Equal(t, 1, checkpointed)
+
+	labels := processor.accumulations[0].Labels()
+	expected := label.NewSet(label.String("A", "a"), label.Empty("B"))
+	require.True(t, labels.Equals(&expected))
+}
+
+func TestViewCustomAggregator(t *testing.T) {
+	ctx := context.Background()
+	meter, sdk, processor := newSDK(t)
+
+	valuerecorder := Must(meter).NewFloat64ValueRecorder("name.exact")
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.Ungroup, nil, &testAlwaysLastValueAggregatorSelector{}))
+
+	valuerecorder.Record(ctx, 1.0, label.String("A", "a"))
+	valuerecorder.Record(ctx, 2.0, label.String("A", "a"))
+
+	checkpointed := sdk.Collect(ctx)
+	require.Equal(t, 1, checkpointed)
+
+	agg := processor.accumulations[0].Aggregator()
+	require.Equal(t, aggregation.LastValueKind, agg.Aggregation().Kind())
+}
+
+func TestViewBind(t *testing.T) {
+	ctx := context.Background()
+	meter, sdk, processor := newSDK(t)
+
+	valuerecorder := Must(meter).NewFloat64ValueRecorder("name.exact")
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.Ungroup, nil, &testAlwaysLastValueAggregatorSelector{}))
+
+	bindvaluerecorder := valuerecorder.Bind(label.String("A", "a"))
+	defer bindvaluerecorder.Unbind()
+
+	Must(meter).RegisterView(metric.NewView(valuerecorder.SyncImpl(), metric.DropAll, nil, &testAlwaysLastValueAggregatorSelector{}))
+
+	valuerecorder.Record(ctx, 1.0, label.String("A", "a"))
+
+	bindvaluerecorder.Record(ctx, 2.0)
+
+	checkpointed := sdk.Collect(ctx)
+	require.Equal(t, 2, checkpointed)
+
+	require.Equal(t, 2, len(processor.accumulations))
+	v0, _, _ := processor.accumulations[0].Aggregator().Aggregation().(aggregation.LastValue).LastValue()
+	v1, _, _ := processor.accumulations[1].Aggregator().Aggregation().(aggregation.LastValue).LastValue()
+	result := map[label.Set]float64{
+		*processor.accumulations[0].Labels(): v0.AsFloat64(),
+		*processor.accumulations[1].Labels(): v1.AsFloat64(),
+	}
+	expected := map[label.Set]float64{
+		label.NewSet():                       1.0,
+		label.NewSet(label.String("A", "a")): 2.0,
+	}
+	require.Equal(t, expected, result)
+}
+
 func TestDisabledInstrument(t *testing.T) {
 	ctx := context.Background()
 	meter, sdk, processor := newSDK(t)
diff --git a/sdk/metric/sdk.go b/sdk/metric/sdk.go
index d2cc369b8c8..201d00a8675 100644
--- a/sdk/metric/sdk.go
+++ b/sdk/metric/sdk.go
@@ -18,6 +18,8 @@ import (
 	"context"
 	"fmt"
 	"runtime"
+	"sort"
+	"strings"
 	"sync"
 	"sync/atomic"
 
@@ -71,6 +73,21 @@ type (
 
 	syncInstrument struct {
 		instrument
+
+		// views is a logical set of registered views for this instrument.
+		views sync.Map
+	}
+
+	// syncInstrumentViewKey is used only in syncInstrument as a key representation of a view.
+	syncInstrumentViewKey struct {
+		selector           metric.AggregatorSelector
+		labelConfig        metric.ViewLabelConfig
+		labelKeysSignature string
+	}
+
+	// syncInstrumentViewValue is used only in syncInstrument as a value representation of a view.
+	syncInstrumentViewValue struct {
+		labelKeys map[label.Key]struct{}
 	}
 
 	// mapkey uniquely describes a metric instrument in terms of
@@ -80,6 +97,11 @@ type (
 		ordered    label.Distinct
 	}
 
+	// boundInstrument is a snapshot of the view data for a given instrument.
+	boundInstrument struct {
+		records []*record
+	}
+
 	// record maintains the state of one metric instrument.  Due
 	// the use of lock-free algorithms, there may be more than one
 	// `record` in existence at a time, although at most one can
@@ -115,6 +137,9 @@ type (
 		// inst is a pointer to the corresponding instrument.
 		inst *syncInstrument
 
+		// viewSelector is a reference to the corresponding view's aggregator selector.
+		viewSelector metric.AggregatorSelector
+
 		// current implements the actual RecordOne() API,
 		// depending on the type of aggregation.  If nil, the
 		// metric was disabled by the exporter.
@@ -146,6 +171,7 @@ var (
 	_ metric.AsyncImpl     = &asyncInstrument{}
 	_ metric.SyncImpl      = &syncInstrument{}
 	_ metric.BoundSyncImpl = &record{}
+	_ metric.BoundSyncImpl = &boundInstrument{}
 
 	ErrUninitializedInstrument = fmt.Errorf("use of an uninitialized instrument")
 )
@@ -158,6 +184,98 @@ func (a *asyncInstrument) Implementation() interface{} {
 	return a
 }
 
+func (s *syncInstrument) registerView(labelConfig metric.ViewLabelConfig, labelKeys []label.Key, selector metric.AggregatorSelector) {
+	key, val := newSyncInstrumentView(labelConfig, labelKeys, selector)
+
+	// First-write-win: ignore duplicated view silently.
+	// maybe return/record an error?
+	s.views.LoadOrStore(key, val)
+}
+
+func (s *syncInstrument) rangeViews(kvs []label.KeyValue, f func([]label.KeyValue, metric.AggregatorSelector)) {
+	empty := true
+	s.views.Range(func(key, value interface{}) bool {
+		empty = false
+		return false
+	})
+	if empty {
+		s.registerView(metric.Ungroup, nil, nil)
+	}
+
+	// compute on need
+	var labelKvs map[label.Key]label.KeyValue
+
+	s.views.Range(func(key, value interface{}) bool {
+		viewKey := key.(*syncInstrumentViewKey)
+		viewValue := value.(*syncInstrumentViewValue)
+
+		var viewLabelKeyValues []label.KeyValue
+		switch viewKey.labelConfig {
+		case metric.Ungroup:
+			viewLabelKeyValues = kvs
+
+		case metric.LabelKeys:
+			if labelKvs == nil {
+				labelKvs = map[label.Key]label.KeyValue{}
+				for _, kv := range kvs {
+					labelKvs[kv.Key] = kv
+				}
+			}
+			for k, kv := range labelKvs {
+				if _, p := viewValue.labelKeys[k]; p {
+					viewLabelKeyValues = append(viewLabelKeyValues, kv)
+				}
+			}
+			for k := range viewValue.labelKeys {
+				if _, p := labelKvs[k]; !p {
+					viewLabelKeyValues = append(viewLabelKeyValues, k.Empty())
+				}
+			}
+
+		case metric.DropAll:
+			// keep nil
+		default:
+			panic(fmt.Sprintf("impossible label config: %s", viewKey.labelConfig))
+		}
+
+		f(viewLabelKeyValues, viewKey.selector)
+		return true
+	})
+}
+
+// newSyncInstrumentView returns a view key/value representation for the given parameters.
+func newSyncInstrumentView(labelConfig metric.ViewLabelConfig, labelKeys []label.Key, selector metric.AggregatorSelector) (*syncInstrumentViewKey, *syncInstrumentViewValue) {
+	key := &syncInstrumentViewKey{
+		selector:           selector,
+		labelConfig:        labelConfig,
+		labelKeysSignature: "",
+	}
+	value := &syncInstrumentViewValue{
+		labelKeys: nil,
+	}
+
+	if labelConfig == metric.LabelKeys {
+		if len(labelKeys) > 0 {
+			value.labelKeys = map[label.Key]struct{}{}
+			for _, k := range labelKeys {
+				value.labelKeys[k] = struct{}{}
+			}
+
+			keys := make([]string, 0, len(value.labelKeys))
+			for k := range value.labelKeys {
+				keys = append(keys, string(k))
+			}
+			sort.Strings(keys)
+			key.labelKeysSignature = strings.Join(keys, "|")
+		} else {
+			// make sure there is only one representation for aggregations without any labels
+			key.labelConfig = metric.DropAll
+		}
+	}
+
+	return key, value
+}
+
 func (s *syncInstrument) Implementation() interface{} {
 	return s
 }
@@ -209,21 +327,18 @@ func (a *asyncInstrument) getRecorder(labels *label.Set) metric.Aggregator {
 // support re-use of the orderedLabels computed by a previous
 // measurement in the same batch.   This performs two allocations
 // in the common case.
-func (s *syncInstrument) acquireHandle(kvs []label.KeyValue, labelPtr *label.Set) *record {
+func (s *syncInstrument) acquireHandle(kvs []label.KeyValue, selector metric.AggregatorSelector) *record {
 	var rec *record
 	var equiv label.Distinct
 
-	if labelPtr == nil {
-		// This memory allocation may not be used, but it's
-		// needed for the `sortSlice` field, to avoid an
-		// allocation while sorting.
-		rec = &record{}
-		rec.storage = label.NewSetWithSortable(kvs, &rec.sortSlice)
-		rec.labels = &rec.storage
-		equiv = rec.storage.Equivalent()
-	} else {
-		equiv = labelPtr.Equivalent()
-	}
+	// This memory allocation may not be used, but it's
+	// needed for the `sortSlice` field, to avoid an
+	// allocation while sorting.
+	rec = &record{}
+	rec.storage = label.NewSetWithSortable(kvs, &rec.sortSlice)
+	rec.labels = &rec.storage
+	rec.viewSelector = selector
+	equiv = rec.storage.Equivalent()
 
 	// Create lookup key for sync.Map (one allocation, as this
 	// passes through an interface{})
@@ -243,14 +358,14 @@ func (s *syncInstrument) acquireHandle(kvs []label.KeyValue, labelPtr *label.Set
 		// This entry is no longer mapped, try to add a new entry.
 	}
 
-	if rec == nil {
-		rec = &record{}
-		rec.labels = labelPtr
-	}
 	rec.refMapped = refcountMapped{value: 2}
 	rec.inst = s
 
-	s.meter.processor.AggregatorFor(&s.descriptor, &rec.current, &rec.checkpoint)
+	if selector != nil {
+		selector.AggregatorFor(&s.descriptor, &rec.current, &rec.checkpoint)
+	} else {
+		s.meter.processor.AggregatorFor(&s.descriptor, &rec.current, &rec.checkpoint)
+	}
 
 	for {
 		// Load/Store: there's a memory allocation to place `mk` into
@@ -283,13 +398,19 @@ func (s *syncInstrument) acquireHandle(kvs []label.KeyValue, labelPtr *label.Set
 }
 
 func (s *syncInstrument) Bind(kvs []label.KeyValue) metric.BoundSyncImpl {
-	return s.acquireHandle(kvs, nil)
+	result := &boundInstrument{}
+	s.rangeViews(kvs, func(viewKvs []label.KeyValue, selector metric.AggregatorSelector) {
+		result.records = append(result.records, s.acquireHandle(viewKvs, selector))
+	})
+	return result
 }
 
 func (s *syncInstrument) RecordOne(ctx context.Context, num number.Number, kvs []label.KeyValue) {
-	h := s.acquireHandle(kvs, nil)
-	defer h.Unbind()
-	h.RecordOne(ctx, num)
+	s.rangeViews(kvs, func(viewKvs []label.KeyValue, selector metric.AggregatorSelector) {
+		h := s.acquireHandle(viewKvs, selector)
+		h.RecordOne(ctx, num)
+		h.Unbind()
+	})
 }
 
 // NewAccumulator constructs a new Accumulator for the given
@@ -310,7 +431,11 @@ func NewAccumulator(processor export.Processor, resource *resource.Resource) *Ac
 }
 
 func (m *Accumulator) RegisterView(v metric.View) {
-	panic("me")
+	s := m.fromSync(v.SyncImpl())
+	// maybe return an error if s is `nil`?
+	if s != nil {
+		s.registerView(v.LabelConfig(), v.LabelKeys(), v.AggregatorFactory())
+	}
 }
 
 // NewSyncInstrument implements metric.MetricImpl.
@@ -437,7 +562,7 @@ func (m *Accumulator) checkpointRecord(r *record) int {
 		return 0
 	}
 
-	a := export.NewAccumulation(&r.inst.descriptor, r.labels, m.resource, r.checkpoint, nil)
+	a := export.NewAccumulation(&r.inst.descriptor, r.labels, m.resource, r.checkpoint, r.viewSelector)
 	err = m.processor.Process(a)
 	if err != nil {
 		otel.Handle(err)
@@ -477,25 +602,12 @@ func (m *Accumulator) checkpointAsync(a *asyncInstrument) int {
 
 // RecordBatch enters a batch of metric events.
 func (m *Accumulator) RecordBatch(ctx context.Context, kvs []label.KeyValue, measurements ...metric.Measurement) {
-	// Labels will be computed the first time acquireHandle is
-	// called.  Subsequent calls to acquireHandle will re-use the
-	// previously computed value instead of recomputing the
-	// ordered labels.
-	var labelsPtr *label.Set
-	for i, meas := range measurements {
+	for _, meas := range measurements {
 		s := m.fromSync(meas.SyncImpl())
 		if s == nil {
 			continue
 		}
-		h := s.acquireHandle(kvs, labelsPtr)
-
-		// Re-use labels for the next measurement.
-		if i == 0 {
-			labelsPtr = h.labels
-		}
-
-		defer h.Unbind()
-		h.RecordOne(ctx, meas.Number())
+		s.RecordOne(ctx, meas.Number(), kvs)
 	}
 }
 
@@ -530,6 +642,18 @@ func (r *record) mapkey() mapkey {
 	}
 }
 
+func (b *boundInstrument) RecordOne(ctx context.Context, number number.Number) {
+	for _, r := range b.records {
+		r.RecordOne(ctx, number)
+	}
+}
+
+func (b *boundInstrument) Unbind() {
+	for _, r := range b.records {
+		r.Unbind()
+	}
+}
+
 // fromSync gets a sync implementation object, checking for
 // uninitialized instruments and instruments created by another SDK.
 func (m *Accumulator) fromSync(sync metric.SyncImpl) *syncInstrument {

From c51df0b9767ec5e89368d1eb2dbca3d316a6d402 Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 10:34:02 +1100
Subject: [PATCH 6/9] add an example of the Metric View API

---
 example/otel-collector/main.go | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/example/otel-collector/main.go b/example/otel-collector/main.go
index 249ca9e85f4..566094c409b 100644
--- a/example/otel-collector/main.go
+++ b/example/otel-collector/main.go
@@ -106,20 +106,30 @@ func main() {
 	tracer := otel.Tracer("test-tracer")
 	meter := otel.Meter("test-meter")
 
+	// Recorder metric example
+	vr, _ := meter.NewFloat64Counter(
+		"an_important_metric",
+		metric.WithDescription("Measures the cumulative epicness of the app"),
+	)
+
+	// DropAll view, meaning all records label would be dropped before aggregation.
+	meter.RegisterView(metric.NewView(vr.SyncImpl(), metric.DropAll, nil, nil))
+
+	// Ungroup view, meaning all records take the labels directly.
+	meter.RegisterView(metric.NewView(vr.SyncImpl(), metric.Ungroup, nil, nil))
+
+	// Two views with the same metric and aggregation type but different label keys for aggregation.
+	meter.RegisterView(metric.NewView(vr.SyncImpl(), metric.LabelKeys, []label.Key{"os_type"}, nil))
+	meter.RegisterView(metric.NewView(vr.SyncImpl(), metric.LabelKeys, []label.Key{"environment"}, nil))
+
 	// labels represent additional key-value descriptors that can be bound to a
 	// metric observer or recorder.
 	commonLabels := []label.KeyValue{
-		label.String("labelA", "chocolate"),
-		label.String("labelB", "raspberry"),
-		label.String("labelC", "vanilla"),
+		label.String("os_type", "linux"),
 	}
 
-	// Recorder metric example
-	valuerecorder := metric.Must(meter).
-		NewFloat64Counter(
-			"an_important_metric",
-			metric.WithDescription("Measures the cumulative epicness of the app"),
-		).Bind(commonLabels...)
+	// Note: views registered after binding have no effect on the bind object.
+	valuerecorder := vr.Bind(commonLabels...)
 	defer valuerecorder.Unbind()
 
 	// work begins
@@ -133,6 +143,10 @@ func main() {
 		log.Printf("Doing really hard work (%d / 10)\n", i+1)
 		valuerecorder.Add(ctx, 1.0)
 
+		vr.Add(context.Background(), 1.0, label.String("os_type", "win"), label.String("environment", "prod"))
+
+		vr.Add(context.Background(), 1.0, label.String("environment", "ddev"))
+
 		<-time.After(time.Second)
 		iSpan.End()
 	}

From 50f51a661279a8ae89cf91875bb86b7fb1cb2ce0 Mon Sep 17 00:00:00 2001
From: beanliu <bean.liu89@gmail.com>
Date: Mon, 18 Jan 2021 13:31:04 +1100
Subject: [PATCH 7/9] update CHANGELOG

---
 CHANGELOG.md | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c624b9fe251..2a88d50f56b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,17 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Added
+
+- Add `View` and `RegisterView` as part of the Metric API, and their implementation in the SDK. (#1473)
+
+### Changed
+
+- Moved `Aggregator`/`Aggregation`/`AggregatorSelector` interfaces to _otel/metric_ from _otel/sdk/export/metric_. (#1473)
+- Support `KeyValue` labels with values unset. (#1473)
+- Modified the `otel-collector` example to include View API usage. (#1473)
+- `Accumulation` accepts a view selector for aggregator creation. (#1473)
+
 ## [0.16.0] - 2020-01-13
 
 ### Added

From bcc48c0c47561774b3fb766a33e45410a900e6c8 Mon Sep 17 00:00:00 2001
From: Raymond Wang <rwang2@atlassian.com>
Date: Wed, 20 Jan 2021 11:23:11 +1100
Subject: [PATCH 8/9] Added fixed bucket histogram view example using simple
 aggregation selector

---
 example/otel-collector/main.go | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/example/otel-collector/main.go b/example/otel-collector/main.go
index 566094c409b..3bad3305620 100644
--- a/example/otel-collector/main.go
+++ b/example/otel-collector/main.go
@@ -31,6 +31,7 @@ import (
 	"go.opentelemetry.io/otel/label"
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/sdk/metric/aggregator/histogram"
 	controller "go.opentelemetry.io/otel/sdk/metric/controller/basic"
 	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
 	"go.opentelemetry.io/otel/sdk/metric/selector/simple"
@@ -122,6 +123,16 @@ func main() {
 	meter.RegisterView(metric.NewView(vr.SyncImpl(), metric.LabelKeys, []label.Key{"os_type"}, nil))
 	meter.RegisterView(metric.NewView(vr.SyncImpl(), metric.LabelKeys, []label.Key{"environment"}, nil))
 
+	// ValueRecorder histogram metric example
+	hist, _ := meter.NewFloat64ValueRecorder(
+		"example_hist",
+		metric.WithDescription("Example fixed bucket histogram"))
+
+	// Custom defined fixed bucket histogram aggregation
+	definedBuckets := []float64{1.0, 2.0, 3.0}
+	histogramAggregatorSelector := simple.NewWithHistogramDistribution(histogram.WithExplicitBoundaries(definedBuckets))
+	meter.RegisterView(metric.NewView(hist.SyncImpl(), metric.Ungroup, nil, histogramAggregatorSelector))
+
 	// labels represent additional key-value descriptors that can be bound to a
 	// metric observer or recorder.
 	commonLabels := []label.KeyValue{
@@ -147,6 +158,8 @@ func main() {
 
 		vr.Add(context.Background(), 1.0, label.String("environment", "ddev"))
 
+		hist.Record(context.Background(), float64(i%5))
+
 		<-time.After(time.Second)
 		iSpan.End()
 	}

From cb00cdf0569021c3e0e4701b8c3cc73806a15fa3 Mon Sep 17 00:00:00 2001
From: Raymond Wang <rwang2@atlassian.com>
Date: Wed, 20 Jan 2021 11:28:59 +1100
Subject: [PATCH 9/9] Wrapped aggregation selector constructor

---
 example/otel-collector/main.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/example/otel-collector/main.go b/example/otel-collector/main.go
index 3bad3305620..038da37cdcd 100644
--- a/example/otel-collector/main.go
+++ b/example/otel-collector/main.go
@@ -130,7 +130,7 @@ func main() {
 
 	// Custom defined fixed bucket histogram aggregation
 	definedBuckets := []float64{1.0, 2.0, 3.0}
-	histogramAggregatorSelector := simple.NewWithHistogramDistribution(histogram.WithExplicitBoundaries(definedBuckets))
+	histogramAggregatorSelector := NewHistogramAggregationSelector(definedBuckets)
 	meter.RegisterView(metric.NewView(hist.SyncImpl(), metric.Ungroup, nil, histogramAggregatorSelector))
 
 	// labels represent additional key-value descriptors that can be bound to a
@@ -172,3 +172,7 @@ func handleErr(err error, message string) {
 		log.Fatalf("%s: %v", message, err)
 	}
 }
+
+func NewHistogramAggregationSelector(buckets []float64) metric.AggregatorSelector {
+	return simple.NewWithHistogramDistribution(histogram.WithExplicitBoundaries(buckets))
+}