From d7cc77b2c46a532a24e37cad624ac7703f9dd30e Mon Sep 17 00:00:00 2001
From: David Ashpole <dashpole@google.com>
Date: Tue, 27 Aug 2024 20:35:56 +0000
Subject: [PATCH] move drop and filtered reservoir types to internal/aggregate

---
 CHANGELOG.md                                  |  7 +++
 sdk/metric/exemplar.go                        | 13 ++---
 sdk/metric/exemplar/filtered_reservoir.go     | 49 ------------------
 sdk/metric/internal/aggregate/aggregate.go    |  9 ++--
 .../internal/aggregate/aggregate_test.go      |  5 +-
 .../{exemplar => internal/aggregate}/drop.go  |  9 ++--
 .../aggregate}/drop_test.go                   |  8 +--
 .../aggregate/exponential_histogram.go        |  7 ++-
 .../internal/aggregate/filtered_reservoir.go  | 50 +++++++++++++++++++
 sdk/metric/internal/aggregate/histogram.go    |  9 ++--
 sdk/metric/internal/aggregate/lastvalue.go    |  9 ++--
 sdk/metric/internal/aggregate/sum.go          | 11 ++--
 12 files changed, 96 insertions(+), 90 deletions(-)
 delete mode 100644 sdk/metric/exemplar/filtered_reservoir.go
 rename sdk/metric/{exemplar => internal/aggregate}/drop.go (51%)
 rename sdk/metric/{exemplar => internal/aggregate}/drop_test.go (77%)
 create mode 100644 sdk/metric/internal/aggregate/filtered_reservoir.go

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ced02a23eec4..7c0100031807 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,13 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Added
+
+- Add `go.opentelemetry.io/otel/sdk/metric/exemplar` package which includes
+  `Exemplar`, `Filter`, `SampledFilter`, `AlwaysOnFilter`, `Histogram`,
+  `FixedSize`, `Reservoir`, `Value` and `ValueType` types. These will be used
+  for configuring the exemplar reservoir for the metrics sdk. (#5747)
+
 ### Removed
 
 - Drop support for [Go 1.21]. (#5736)
diff --git a/sdk/metric/exemplar.go b/sdk/metric/exemplar.go
index 1cee6b11bdd1..5850e46768ef 100644
--- a/sdk/metric/exemplar.go
+++ b/sdk/metric/exemplar.go
@@ -9,6 +9,7 @@ import (
 	"slices"
 
 	"go.opentelemetry.io/otel/sdk/metric/exemplar"
+	"go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
 	"go.opentelemetry.io/otel/sdk/metric/internal/x"
 )
 
@@ -19,7 +20,7 @@ import (
 // Note: This will only return non-nil values when the experimental exemplar
 // feature is enabled and the OTEL_METRICS_EXEMPLAR_FILTER environment variable
 // is not set to always_off.
-func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.FilteredReservoir[N] {
+func reservoirFunc[N int64 | float64](agg Aggregation) func() aggregate.FilteredExemplarReservoir[N] {
 	if !x.Exemplars.Enabled() {
 		return nil
 	}
@@ -32,7 +33,7 @@ func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.FilteredR
 	case "always_on":
 		filter = exemplar.AlwaysOnFilter
 	case "always_off":
-		return exemplar.Drop
+		return aggregate.DropReservoir
 	case "trace_based":
 		fallthrough
 	default:
@@ -45,9 +46,9 @@ func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.FilteredR
 	a, ok := agg.(AggregationExplicitBucketHistogram)
 	if ok && len(a.Boundaries) > 0 {
 		cp := slices.Clone(a.Boundaries)
-		return func() exemplar.FilteredReservoir[N] {
+		return func() aggregate.FilteredExemplarReservoir[N] {
 			bounds := cp
-			return exemplar.NewFilteredReservoir[N](filter, exemplar.Histogram(bounds))
+			return aggregate.NewFilteredExemplarReservoir[N](filter, exemplar.Histogram(bounds))
 		}
 	}
 
@@ -75,7 +76,7 @@ func reservoirFunc[N int64 | float64](agg Aggregation) func() exemplar.FilteredR
 		}
 	}
 
-	return func() exemplar.FilteredReservoir[N] {
-		return exemplar.NewFilteredReservoir[N](filter, exemplar.FixedSize(n))
+	return func() aggregate.FilteredExemplarReservoir[N] {
+		return aggregate.NewFilteredExemplarReservoir[N](filter, exemplar.FixedSize(n))
 	}
 }
diff --git a/sdk/metric/exemplar/filtered_reservoir.go b/sdk/metric/exemplar/filtered_reservoir.go
deleted file mode 100644
index 29a718219192..000000000000
--- a/sdk/metric/exemplar/filtered_reservoir.go
+++ /dev/null
@@ -1,49 +0,0 @@
-// Copyright The OpenTelemetry Authors
-// SPDX-License-Identifier: Apache-2.0
-
-package exemplar // import "go.opentelemetry.io/otel/sdk/metric/exemplar"
-
-import (
-	"context"
-	"time"
-
-	"go.opentelemetry.io/otel/attribute"
-)
-
-// FilteredReservoir wraps a [Reservoir] with a filter.
-type FilteredReservoir[N int64 | float64] interface {
-	// Offer accepts the parameters associated with a measurement. The
-	// parameters will be stored as an exemplar if the filter decides to
-	// sample the measurement.
-	//
-	// The passed ctx needs to contain any baggage or span that were active
-	// when the measurement was made. This information may be used by the
-	// Reservoir in making a sampling decision.
-	Offer(ctx context.Context, val N, attr []attribute.KeyValue)
-	// Collect returns all the held exemplars in the reservoir.
-	Collect(dest *[]Exemplar)
-}
-
-// filteredReservoir handles the pre-sampled exemplar of measurements made.
-type filteredReservoir[N int64 | float64] struct {
-	filter    Filter
-	reservoir Reservoir
-}
-
-// NewFilteredReservoir creates a [FilteredReservoir] which only offers values
-// that are allowed by the filter.
-func NewFilteredReservoir[N int64 | float64](f Filter, r Reservoir) FilteredReservoir[N] {
-	return &filteredReservoir[N]{
-		filter:    f,
-		reservoir: r,
-	}
-}
-
-func (f *filteredReservoir[N]) Offer(ctx context.Context, val N, attr []attribute.KeyValue) {
-	if f.filter(ctx) {
-		// only record the current time if we are sampling this measurment.
-		f.reservoir.Offer(ctx, time.Now(), NewValue(val), attr)
-	}
-}
-
-func (f *filteredReservoir[N]) Collect(dest *[]Exemplar) { f.reservoir.Collect(dest) }
diff --git a/sdk/metric/internal/aggregate/aggregate.go b/sdk/metric/internal/aggregate/aggregate.go
index 1c4c3dc9ad0d..f1f3ab673142 100644
--- a/sdk/metric/internal/aggregate/aggregate.go
+++ b/sdk/metric/internal/aggregate/aggregate.go
@@ -8,7 +8,6 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -38,8 +37,8 @@ type Builder[N int64 | float64] struct {
 	// create new exemplar reservoirs for a new seen attribute set.
 	//
 	// If this is not provided a default factory function that returns an
-	// exemplar.Drop reservoir will be used.
-	ReservoirFunc func() exemplar.FilteredReservoir[N]
+	// DropReservoir reservoir will be used.
+	ReservoirFunc func() FilteredExemplarReservoir[N]
 	// AggregationLimit is the cardinality limit of measurement attributes. Any
 	// measurement for new attributes once the limit has been reached will be
 	// aggregated into a single aggregate for the "otel.metric.overflow"
@@ -50,12 +49,12 @@ type Builder[N int64 | float64] struct {
 	AggregationLimit int
 }
 
-func (b Builder[N]) resFunc() func() exemplar.FilteredReservoir[N] {
+func (b Builder[N]) resFunc() func() FilteredExemplarReservoir[N] {
 	if b.ReservoirFunc != nil {
 		return b.ReservoirFunc
 	}
 
-	return exemplar.Drop
+	return DropReservoir
 }
 
 type fltrMeasure[N int64 | float64] func(ctx context.Context, value N, fltrAttr attribute.Set, droppedAttr []attribute.KeyValue)
diff --git a/sdk/metric/internal/aggregate/aggregate_test.go b/sdk/metric/internal/aggregate/aggregate_test.go
index 413070e6d3d0..fec39f5f9192 100644
--- a/sdk/metric/internal/aggregate/aggregate_test.go
+++ b/sdk/metric/internal/aggregate/aggregate_test.go
@@ -13,7 +13,6 @@ import (
 	"github.com/stretchr/testify/assert"
 
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
 )
@@ -73,8 +72,8 @@ func (c *clock) Register() (unregister func()) {
 	return func() { now = orig }
 }
 
-func dropExemplars[N int64 | float64]() exemplar.FilteredReservoir[N] {
-	return exemplar.Drop[N]()
+func dropExemplars[N int64 | float64]() FilteredExemplarReservoir[N] {
+	return DropReservoir[N]()
 }
 
 func TestBuilderFilter(t *testing.T) {
diff --git a/sdk/metric/exemplar/drop.go b/sdk/metric/internal/aggregate/drop.go
similarity index 51%
rename from sdk/metric/exemplar/drop.go
rename to sdk/metric/internal/aggregate/drop.go
index 33713c45670c..4a3d4cc22186 100644
--- a/sdk/metric/exemplar/drop.go
+++ b/sdk/metric/internal/aggregate/drop.go
@@ -1,16 +1,17 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package exemplar // import "go.opentelemetry.io/otel/sdk/metric/exemplar"
+package aggregate // import "go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
 
 import (
 	"context"
 
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 )
 
-// Drop returns a [FilteredReservoir] that drops all measurements it is offered.
-func Drop[N int64 | float64]() FilteredReservoir[N] { return &dropRes[N]{} }
+// DropReservoir returns a [FilteredReservoir] that drops all measurements it is offered.
+func DropReservoir[N int64 | float64]() FilteredExemplarReservoir[N] { return &dropRes[N]{} }
 
 type dropRes[N int64 | float64] struct{}
 
@@ -18,6 +19,6 @@ type dropRes[N int64 | float64] struct{}
 func (r *dropRes[N]) Offer(context.Context, N, []attribute.KeyValue) {}
 
 // Collect resets dest. No exemplars will ever be returned.
-func (r *dropRes[N]) Collect(dest *[]Exemplar) {
+func (r *dropRes[N]) Collect(dest *[]exemplar.Exemplar) {
 	*dest = (*dest)[:0]
 }
diff --git a/sdk/metric/exemplar/drop_test.go b/sdk/metric/internal/aggregate/drop_test.go
similarity index 77%
rename from sdk/metric/exemplar/drop_test.go
rename to sdk/metric/internal/aggregate/drop_test.go
index 578b28acd27a..f1d78d0b287c 100644
--- a/sdk/metric/exemplar/drop_test.go
+++ b/sdk/metric/internal/aggregate/drop_test.go
@@ -1,12 +1,14 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package exemplar
+package aggregate
 
 import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 )
 
 func TestDrop(t *testing.T) {
@@ -15,9 +17,9 @@ func TestDrop(t *testing.T) {
 }
 
 func testDropFiltered[N int64 | float64](t *testing.T) {
-	r := Drop[N]()
+	r := DropReservoir[N]()
 
-	var dest []Exemplar
+	var dest []exemplar.Exemplar
 	r.Collect(&dest)
 
 	assert.Len(t, dest, 0, "non-sampled context should not be offered")
diff --git a/sdk/metric/internal/aggregate/exponential_histogram.go b/sdk/metric/internal/aggregate/exponential_histogram.go
index 50a2f6e18973..a4de5674ba19 100644
--- a/sdk/metric/internal/aggregate/exponential_histogram.go
+++ b/sdk/metric/internal/aggregate/exponential_histogram.go
@@ -12,7 +12,6 @@ import (
 
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -31,7 +30,7 @@ const (
 // expoHistogramDataPoint is a single data point in an exponential histogram.
 type expoHistogramDataPoint[N int64 | float64] struct {
 	attrs attribute.Set
-	res   exemplar.FilteredReservoir[N]
+	res   FilteredExemplarReservoir[N]
 
 	count uint64
 	min   N
@@ -284,7 +283,7 @@ func (b *expoBuckets) downscale(delta int32) {
 // newExponentialHistogram returns an Aggregator that summarizes a set of
 // measurements as an exponential histogram. Each histogram is scoped by attributes
 // and the aggregation cycle the measurements were made in.
-func newExponentialHistogram[N int64 | float64](maxSize, maxScale int32, noMinMax, noSum bool, limit int, r func() exemplar.FilteredReservoir[N]) *expoHistogram[N] {
+func newExponentialHistogram[N int64 | float64](maxSize, maxScale int32, noMinMax, noSum bool, limit int, r func() FilteredExemplarReservoir[N]) *expoHistogram[N] {
 	return &expoHistogram[N]{
 		noSum:    noSum,
 		noMinMax: noMinMax,
@@ -307,7 +306,7 @@ type expoHistogram[N int64 | float64] struct {
 	maxSize  int
 	maxScale int32
 
-	newRes   func() exemplar.FilteredReservoir[N]
+	newRes   func() FilteredExemplarReservoir[N]
 	limit    limiter[*expoHistogramDataPoint[N]]
 	values   map[attribute.Distinct]*expoHistogramDataPoint[N]
 	valuesMu sync.Mutex
diff --git a/sdk/metric/internal/aggregate/filtered_reservoir.go b/sdk/metric/internal/aggregate/filtered_reservoir.go
new file mode 100644
index 000000000000..dee1adccb758
--- /dev/null
+++ b/sdk/metric/internal/aggregate/filtered_reservoir.go
@@ -0,0 +1,50 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package aggregate // import "go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
+
+import (
+	"context"
+	"time"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/metric/exemplar"
+)
+
+// FilteredExemplarReservoir wraps a [exemplar.Reservoir] with a filter.
+type FilteredExemplarReservoir[N int64 | float64] interface {
+	// Offer accepts the parameters associated with a measurement. The
+	// parameters will be stored as an exemplar if the filter decides to
+	// sample the measurement.
+	//
+	// The passed ctx needs to contain any baggage or span that were active
+	// when the measurement was made. This information may be used by the
+	// Reservoir in making a sampling decision.
+	Offer(ctx context.Context, val N, attr []attribute.KeyValue)
+	// Collect returns all the held exemplars in the reservoir.
+	Collect(dest *[]exemplar.Exemplar)
+}
+
+// filteredExemplarReservoir handles the pre-sampled exemplar of measurements made.
+type filteredExemplarReservoir[N int64 | float64] struct {
+	filter    exemplar.Filter
+	reservoir exemplar.Reservoir
+}
+
+// NewFilteredExemplarReservoir creates a [FilteredExemplarReservoir] which only offers values
+// that are allowed by the filter.
+func NewFilteredExemplarReservoir[N int64 | float64](f exemplar.Filter, r exemplar.Reservoir) FilteredExemplarReservoir[N] {
+	return &filteredExemplarReservoir[N]{
+		filter:    f,
+		reservoir: r,
+	}
+}
+
+func (f *filteredExemplarReservoir[N]) Offer(ctx context.Context, val N, attr []attribute.KeyValue) {
+	if f.filter(ctx) {
+		// only record the current time if we are sampling this measurment.
+		f.reservoir.Offer(ctx, time.Now(), exemplar.NewValue(val), attr)
+	}
+}
+
+func (f *filteredExemplarReservoir[N]) Collect(dest *[]exemplar.Exemplar) { f.reservoir.Collect(dest) }
diff --git a/sdk/metric/internal/aggregate/histogram.go b/sdk/metric/internal/aggregate/histogram.go
index f36178db4d21..35d020378bd9 100644
--- a/sdk/metric/internal/aggregate/histogram.go
+++ b/sdk/metric/internal/aggregate/histogram.go
@@ -11,13 +11,12 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
 type buckets[N int64 | float64] struct {
 	attrs attribute.Set
-	res   exemplar.FilteredReservoir[N]
+	res   FilteredExemplarReservoir[N]
 
 	counts   []uint64
 	count    uint64
@@ -48,13 +47,13 @@ type histValues[N int64 | float64] struct {
 	noSum  bool
 	bounds []float64
 
-	newRes   func() exemplar.FilteredReservoir[N]
+	newRes   func() FilteredExemplarReservoir[N]
 	limit    limiter[*buckets[N]]
 	values   map[attribute.Distinct]*buckets[N]
 	valuesMu sync.Mutex
 }
 
-func newHistValues[N int64 | float64](bounds []float64, noSum bool, limit int, r func() exemplar.FilteredReservoir[N]) *histValues[N] {
+func newHistValues[N int64 | float64](bounds []float64, noSum bool, limit int, r func() FilteredExemplarReservoir[N]) *histValues[N] {
 	// The responsibility of keeping all buckets correctly associated with the
 	// passed boundaries is ultimately this type's responsibility. Make a copy
 	// here so we can always guarantee this. Or, in the case of failure, have
@@ -109,7 +108,7 @@ func (s *histValues[N]) measure(ctx context.Context, value N, fltrAttr attribute
 
 // newHistogram returns an Aggregator that summarizes a set of measurements as
 // an histogram.
-func newHistogram[N int64 | float64](boundaries []float64, noMinMax, noSum bool, limit int, r func() exemplar.FilteredReservoir[N]) *histogram[N] {
+func newHistogram[N int64 | float64](boundaries []float64, noMinMax, noSum bool, limit int, r func() FilteredExemplarReservoir[N]) *histogram[N] {
 	return &histogram[N]{
 		histValues: newHistValues[N](boundaries, noSum, limit, r),
 		noMinMax:   noMinMax,
diff --git a/sdk/metric/internal/aggregate/lastvalue.go b/sdk/metric/internal/aggregate/lastvalue.go
index 1194593a482b..a7b5fe572bef 100644
--- a/sdk/metric/internal/aggregate/lastvalue.go
+++ b/sdk/metric/internal/aggregate/lastvalue.go
@@ -9,7 +9,6 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
@@ -17,10 +16,10 @@ import (
 type datapoint[N int64 | float64] struct {
 	attrs attribute.Set
 	value N
-	res   exemplar.FilteredReservoir[N]
+	res   FilteredExemplarReservoir[N]
 }
 
-func newLastValue[N int64 | float64](limit int, r func() exemplar.FilteredReservoir[N]) *lastValue[N] {
+func newLastValue[N int64 | float64](limit int, r func() FilteredExemplarReservoir[N]) *lastValue[N] {
 	return &lastValue[N]{
 		newRes: r,
 		limit:  newLimiter[datapoint[N]](limit),
@@ -33,7 +32,7 @@ func newLastValue[N int64 | float64](limit int, r func() exemplar.FilteredReserv
 type lastValue[N int64 | float64] struct {
 	sync.Mutex
 
-	newRes func() exemplar.FilteredReservoir[N]
+	newRes func() FilteredExemplarReservoir[N]
 	limit  limiter[datapoint[N]]
 	values map[attribute.Distinct]datapoint[N]
 	start  time.Time
@@ -115,7 +114,7 @@ func (s *lastValue[N]) copyDpts(dest *[]metricdata.DataPoint[N], t time.Time) in
 
 // newPrecomputedLastValue returns an aggregator that summarizes a set of
 // observations as the last one made.
-func newPrecomputedLastValue[N int64 | float64](limit int, r func() exemplar.FilteredReservoir[N]) *precomputedLastValue[N] {
+func newPrecomputedLastValue[N int64 | float64](limit int, r func() FilteredExemplarReservoir[N]) *precomputedLastValue[N] {
 	return &precomputedLastValue[N]{lastValue: newLastValue[N](limit, r)}
 }
 
diff --git a/sdk/metric/internal/aggregate/sum.go b/sdk/metric/internal/aggregate/sum.go
index 4c99837c76a7..9fa1d386f59a 100644
--- a/sdk/metric/internal/aggregate/sum.go
+++ b/sdk/metric/internal/aggregate/sum.go
@@ -9,25 +9,24 @@ import (
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/sdk/metric/exemplar"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
 type sumValue[N int64 | float64] struct {
 	n     N
-	res   exemplar.FilteredReservoir[N]
+	res   FilteredExemplarReservoir[N]
 	attrs attribute.Set
 }
 
 // valueMap is the storage for sums.
 type valueMap[N int64 | float64] struct {
 	sync.Mutex
-	newRes func() exemplar.FilteredReservoir[N]
+	newRes func() FilteredExemplarReservoir[N]
 	limit  limiter[sumValue[N]]
 	values map[attribute.Distinct]sumValue[N]
 }
 
-func newValueMap[N int64 | float64](limit int, r func() exemplar.FilteredReservoir[N]) *valueMap[N] {
+func newValueMap[N int64 | float64](limit int, r func() FilteredExemplarReservoir[N]) *valueMap[N] {
 	return &valueMap[N]{
 		newRes: r,
 		limit:  newLimiter[sumValue[N]](limit),
@@ -55,7 +54,7 @@ func (s *valueMap[N]) measure(ctx context.Context, value N, fltrAttr attribute.S
 // newSum returns an aggregator that summarizes a set of measurements as their
 // arithmetic sum. Each sum is scoped by attributes and the aggregation cycle
 // the measurements were made in.
-func newSum[N int64 | float64](monotonic bool, limit int, r func() exemplar.FilteredReservoir[N]) *sum[N] {
+func newSum[N int64 | float64](monotonic bool, limit int, r func() FilteredExemplarReservoir[N]) *sum[N] {
 	return &sum[N]{
 		valueMap:  newValueMap[N](limit, r),
 		monotonic: monotonic,
@@ -144,7 +143,7 @@ func (s *sum[N]) cumulative(dest *metricdata.Aggregation) int {
 // newPrecomputedSum returns an aggregator that summarizes a set of
 // observatrions as their arithmetic sum. Each sum is scoped by attributes and
 // the aggregation cycle the measurements were made in.
-func newPrecomputedSum[N int64 | float64](monotonic bool, limit int, r func() exemplar.FilteredReservoir[N]) *precomputedSum[N] {
+func newPrecomputedSum[N int64 | float64](monotonic bool, limit int, r func() FilteredExemplarReservoir[N]) *precomputedSum[N] {
 	return &precomputedSum[N]{
 		valueMap:  newValueMap[N](limit, r),
 		monotonic: monotonic,