Simplify the histogram implementation

sdk/metric/internal/aggregate/aggregate.go

@@ -16,12 +16,17 @@ package aggregate // import "go.opentelemetry.io/otel/sdk/metric/internal/aggreg
 
 import (
 	"context"
+	"time"
 
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/sdk/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
+// now is used to return the current local time while allowing tests to
+// override the default time.Now function.
+var now = time.Now
+
 // Measure receives measurements to be aggregated.
 type Measure[N int64 | float64] func(context.Context, N, attribute.Set)
 
@@ -53,19 +58,6 @@ func (b Builder[N]) filter(f Measure[N]) Measure[N] {
 	return f
 }
 
-func (b Builder[N]) input(agg aggregator[N]) Measure[N] {
-	if b.Filter != nil {
-		fltr := b.Filter // Copy to make it immutable after assignment.
-		return func(_ context.Context, n N, a attribute.Set) {
-			fAttr, _ := a.Filter(fltr)
-			agg.Aggregate(n, fAttr)
-		}
-	}
-	return func(_ context.Context, n N, a attribute.Set) {
-		agg.Aggregate(n, a)
-	}
-}
-
 // LastValue returns a last-value aggregate function input and output.
 //
 // The Builder.Temporality is ignored and delta is use always.
@@ -111,19 +103,12 @@ func (b Builder[N]) Sum(monotonic bool) (Measure[N], ComputeAggregation) {
 // ExplicitBucketHistogram returns a histogram aggregate function input and
 // output.
 func (b Builder[N]) ExplicitBucketHistogram(cfg aggregation.ExplicitBucketHistogram, noSum bool) (Measure[N], ComputeAggregation) {
-	var h aggregator[N]
+	h := newHistogram[N](cfg, noSum)
 	switch b.Temporality {
 	case metricdata.DeltaTemporality:
-		h = newDeltaHistogram[N](cfg, noSum)
+		return b.filter(h.measure), h.delta
 	default:
-		h = newCumulativeHistogram[N](cfg, noSum)
-	}
-	return b.input(h), func(dest *metricdata.Aggregation) int {
-		// TODO (#4220): optimize memory reuse here.
-		*dest = h.Aggregation()
-
-		hData, _ := (*dest).(metricdata.Histogram[N])
-		return len(hData.DataPoints)
+		return b.filter(h.measure), h.cumulative
 	}
 }
 

sdk/metric/internal/aggregate/aggregate_test.go

@@ -55,21 +55,12 @@ var (
 	}
 )
 
-type inputTester[N int64 | float64] struct {
-	aggregator[N]
-
-	value N
-	attr  attribute.Set
+func TestBuilderFilter(t *testing.T) {
+	t.Run("Int64", testBuilderFilter[int64]())
+	t.Run("Float64", testBuilderFilter[float64]())
 }
 
-func (it *inputTester[N]) Aggregate(v N, a attribute.Set) { it.value, it.attr = v, a }
-
-func TestBuilderInput(t *testing.T) {
-	t.Run("Int64", testBuilderInput[int64]())
-	t.Run("Float64", testBuilderInput[float64]())
-}
-
-func testBuilderInput[N int64 | float64]() func(t *testing.T) {
+func testBuilderFilter[N int64 | float64]() func(t *testing.T) {
 	return func(t *testing.T) {
 		t.Helper()
 
@@ -78,12 +69,11 @@ func testBuilderInput[N int64 | float64]() func(t *testing.T) {
 			return func(t *testing.T) {
 				t.Helper()
 
-				it := &inputTester[N]{}
-				meas := b.input(it)
+				meas := b.filter(func(_ context.Context, v N, a attribute.Set) {
+					assert.Equal(t, value, v, "measured incorrect value")
+					assert.Equal(t, wantA, a, "measured incorrect attributes")
+				})
 				meas(context.Background(), value, attr)
-
-				assert.Equal(t, value, it.value, "measured incorrect value")
-				assert.Equal(t, wantA, it.attr, "measured incorrect attributes")
 			}
 		}