Add temporality selector functions

internal/shared/otlp/otlpmetric/oconf/envconfig.go.tmpl

@@ -18,7 +18,6 @@ import (
 	"{{ .envconfigImportPath }}"
 	"go.opentelemetry.io/otel/internal/global"
 	"go.opentelemetry.io/otel/sdk/metric"
-	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
 // DefaultEnvOptionsReader is the default environments reader.
@@ -165,11 +164,11 @@ func withEnvTemporalityPreference(n string, fn func(metric.TemporalitySelector))
 		if s, ok := e.GetEnvValue(n); ok {
 			switch strings.ToLower(s) {
 			case "cumulative":
-				fn(cumulativeTemporality)
+				fn(metric.CumulativeTemporalitySelector)
 			case "delta":
-				fn(deltaTemporality)
+				fn(metric.DeltaTemporalitySelector)
 			case "lowmemory":
-				fn(lowMemory)
+				fn(metric.LowMemoryTemporalitySelector)
 			default:
 				global.Warn(
 					"OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE is set to an invalid value, ignoring.",
@@ -181,28 +180,6 @@ func withEnvTemporalityPreference(n string, fn func(metric.TemporalitySelector))
 	}
 }
 
-func cumulativeTemporality(metric.InstrumentKind) metricdata.Temporality {
-	return metricdata.CumulativeTemporality
-}
-
-func deltaTemporality(ik metric.InstrumentKind) metricdata.Temporality {
-	switch ik {
-	case metric.InstrumentKindCounter, metric.InstrumentKindHistogram, metric.InstrumentKindObservableCounter:
-		return metricdata.DeltaTemporality
-	default:
-		return metricdata.CumulativeTemporality
-	}
-}
-
-func lowMemory(ik metric.InstrumentKind) metricdata.Temporality {
-	switch ik {
-	case metric.InstrumentKindCounter, metric.InstrumentKindHistogram:
-		return metricdata.DeltaTemporality
-	default:
-		return metricdata.CumulativeTemporality
-	}
-}
-
 func withEnvAggPreference(n string, fn func(metric.AggregationSelector)) func(e *envconfig.EnvOptionsReader) {
 	return func(e *envconfig.EnvOptionsReader) {
 		if s, ok := e.GetEnvValue(n); ok {

sdk/metric/reader.go

@@ -127,10 +127,40 @@ type TemporalitySelector func(InstrumentKind) metricdata.Temporality
 // DefaultTemporalitySelector is the default TemporalitySelector used if
 // WithTemporalitySelector is not provided. CumulativeTemporality will be used
 // for all instrument kinds if this TemporalitySelector is used.
-func DefaultTemporalitySelector(InstrumentKind) metricdata.Temporality {
+func DefaultTemporalitySelector(k InstrumentKind) metricdata.Temporality {
+	return CumulativeTemporalitySelector(k)
+}
+
+// CumulativeTemporalitySelector is the TemporalitySelector that uses
+// a cumulative temporality for all instrument kinds.
+func CumulativeTemporalitySelector(InstrumentKind) metricdata.Temporality {
 	return metricdata.CumulativeTemporality
 }
 
+// DeltaTemporalitySelector is the TemporalitySelector that uses
+// a delta temporality for instrument kinds: counter, histogram, observable counter
+// All other instruments use cumulative temporality.
+func DeltaTemporalitySelector(k InstrumentKind) metricdata.Temporality {
+	switch k {
+	case InstrumentKindCounter, InstrumentKindHistogram, InstrumentKindObservableCounter:
+		return metricdata.DeltaTemporality
+	default:
+		return metricdata.CumulativeTemporality
+	}
+}
+
+// LowMemoryTemporalitySelector is the TemporalitySelector that uses
+// delta temporality for counters and histograms. All other instruments use
+// cumulative temporality.
+func LowMemoryTemporalitySelector(k InstrumentKind) metricdata.Temporality {
+	switch k {
+	case InstrumentKindCounter, InstrumentKindHistogram:
+		return metricdata.DeltaTemporality
+	default:
+		return metricdata.CumulativeTemporality
+	}
+}
+
 // AggregationSelector selects the aggregation and the parameters to use for
 // that aggregation based on the InstrumentKind.
 //