PoC: Metric instruments support an WithOptIn option.

metric/asyncfloat64.go

@@ -43,6 +43,7 @@ type Float64ObservableCounter interface {
 type Float64ObservableCounterConfig struct {
 	description string
 	unit        string
+	optIn       bool
 	callbacks   []Float64Callback
 }
 
@@ -66,6 +67,11 @@ func (c Float64ObservableCounterConfig) Unit() string {
 	return c.unit
 }
 
+// OptIn returns true if the instrument is disabled by default.
+func (c Float64ObservableCounterConfig) OptIn() bool {
+	return c.optIn
+}
+
 // Callbacks returns the configured callbacks.
 func (c Float64ObservableCounterConfig) Callbacks() []Float64Callback {
 	return c.callbacks
@@ -101,6 +107,7 @@ type Float64ObservableUpDownCounter interface {
 type Float64ObservableUpDownCounterConfig struct {
 	description string
 	unit        string
+	optIn       bool
 	callbacks   []Float64Callback
 }
 
@@ -126,6 +133,11 @@ func (c Float64ObservableUpDownCounterConfig) Unit() string {
 	return c.unit
 }
 
+// OptIn returns true if the instrument is disabled by default.
+func (c Float64ObservableUpDownCounterConfig) OptIn() bool {
+	return c.optIn
+}
+
 // Callbacks returns the configured callbacks.
 func (c Float64ObservableUpDownCounterConfig) Callbacks() []Float64Callback {
 	return c.callbacks
@@ -160,6 +172,7 @@ type Float64ObservableGauge interface {
 type Float64ObservableGaugeConfig struct {
 	description string
 	unit        string
+	optIn       bool
 	callbacks   []Float64Callback
 }
 
@@ -183,6 +196,11 @@ func (c Float64ObservableGaugeConfig) Unit() string {
 	return c.unit
 }
 
+// OptIn returns true if the instrument is disabled by default.
+func (c Float64ObservableGaugeConfig) OptIn() bool {
+	return c.optIn
+}
+
 // Callbacks returns the configured callbacks.
 func (c Float64ObservableGaugeConfig) Callbacks() []Float64Callback {
 	return c.callbacks

metric/asyncfloat64_test.go

@@ -18,12 +18,14 @@ func TestFloat64ObservableConfiguration(t *testing.T) {
 		token  float64 = 43
 		desc           = "Instrument description."
 		uBytes         = "By"
+		optIn          = true
 	)
 
 	run := func(got float64ObservableConfig) func(*testing.T) {
 		return func(t *testing.T) {
 			assert.Equal(t, desc, got.Description(), "description")
 			assert.Equal(t, uBytes, got.Unit(), "unit")
+			assert.Equal(t, optIn, got.OptIn(), "optIn")
 
 			// Functions are not comparable.
 			cBacks := got.Callbacks()
@@ -44,6 +46,7 @@ func TestFloat64ObservableConfiguration(t *testing.T) {
 		NewFloat64ObservableCounterConfig(
 			WithDescription(desc),
 			WithUnit(uBytes),
+			WithOptIn(),
 			WithFloat64Callback(cback),
 		),
 	))
@@ -52,6 +55,7 @@ func TestFloat64ObservableConfiguration(t *testing.T) {
 		NewFloat64ObservableUpDownCounterConfig(
 			WithDescription(desc),
 			WithUnit(uBytes),
+			WithOptIn(),
 			WithFloat64Callback(cback),
 		),
 	))
@@ -60,6 +64,7 @@ func TestFloat64ObservableConfiguration(t *testing.T) {
 		NewFloat64ObservableGaugeConfig(
 			WithDescription(desc),
 			WithUnit(uBytes),
+			WithOptIn(),
 			WithFloat64Callback(cback),
 		),
 	))
@@ -68,6 +73,7 @@ func TestFloat64ObservableConfiguration(t *testing.T) {
 type float64ObservableConfig interface {
 	Description() string
 	Unit() string
+	OptIn() bool
 	Callbacks() []Float64Callback
 }
 

metric/asyncint64.go

@@ -42,6 +42,7 @@ type Int64ObservableCounter interface {
 type Int64ObservableCounterConfig struct {
 	description string
 	unit        string
+	optIn       bool
 	callbacks   []Int64Callback
 }
 
@@ -65,6 +66,11 @@ func (c Int64ObservableCounterConfig) Unit() string {
 	return c.unit
 }
 
+// OptIn returns true if the instrument is disabled by default.
+func (c Int64ObservableCounterConfig) OptIn() bool {
+	return c.optIn
+}
+
 // Callbacks returns the configured callbacks.
 func (c Int64ObservableCounterConfig) Callbacks() []Int64Callback {
 	return c.callbacks
@@ -100,6 +106,7 @@ type Int64ObservableUpDownCounter interface {
 type Int64ObservableUpDownCounterConfig struct {
 	description string
 	unit        string
+	optIn       bool
 	callbacks   []Int64Callback
 }
 
@@ -125,6 +132,11 @@ func (c Int64ObservableUpDownCounterConfig) Unit() string {
 	return c.unit
 }
 
+// OptIn returns true if the instrument is disabled by default.
+func (c Int64ObservableUpDownCounterConfig) OptIn() bool {
+	return c.optIn
+}
+
 // Callbacks returns the configured callbacks.
 func (c Int64ObservableUpDownCounterConfig) Callbacks() []Int64Callback {
 	return c.callbacks
@@ -159,6 +171,7 @@ type Int64ObservableGauge interface {
 type Int64ObservableGaugeConfig struct {
 	description string
 	unit        string
+	optIn       bool
 	callbacks   []Int64Callback
 }
 
@@ -182,6 +195,11 @@ func (c Int64ObservableGaugeConfig) Unit() string {
 	return c.unit
 }
 
+// OptIn returns true if the instrument is disabled by default.
+func (c Int64ObservableGaugeConfig) OptIn() bool {
+	return c.optIn
+}
+
 // Callbacks returns the configured callbacks.
 func (c Int64ObservableGaugeConfig) Callbacks() []Int64Callback {
 	return c.callbacks

metric/asyncint64_test.go

@@ -18,12 +18,14 @@ func TestInt64ObservableConfiguration(t *testing.T) {
 		token  int64 = 43
 		desc         = "Instrument description."
 		uBytes       = "By"
+		optIn        = true
 	)
 
 	run := func(got int64ObservableConfig) func(*testing.T) {
 		return func(t *testing.T) {
 			assert.Equal(t, desc, got.Description(), "description")
 			assert.Equal(t, uBytes, got.Unit(), "unit")
+			assert.Equal(t, optIn, got.OptIn(), "optIn")
 
 			// Functions are not comparable.
 			cBacks := got.Callbacks()
@@ -44,6 +46,7 @@ func TestInt64ObservableConfiguration(t *testing.T) {
 		NewInt64ObservableCounterConfig(
 			WithDescription(desc),
 			WithUnit(uBytes),
+			WithOptIn(),
 			WithInt64Callback(cback),
 		),
 	))
@@ -52,6 +55,7 @@ func TestInt64ObservableConfiguration(t *testing.T) {
 		NewInt64ObservableUpDownCounterConfig(
 			WithDescription(desc),
 			WithUnit(uBytes),
+			WithOptIn(),
 			WithInt64Callback(cback),
 		),
 	))
@@ -60,6 +64,7 @@ func TestInt64ObservableConfiguration(t *testing.T) {
 		NewInt64ObservableGaugeConfig(
 			WithDescription(desc),
 			WithUnit(uBytes),
+			WithOptIn(),
 			WithInt64Callback(cback),
 		),
 	))
@@ -68,6 +73,7 @@ func TestInt64ObservableConfiguration(t *testing.T) {
 type int64ObservableConfig interface {
 	Description() string
 	Unit() string
+	OptIn() bool
 	Callbacks() []Int64Callback
 }
 

metric/example_test.go

@@ -301,3 +301,23 @@ func ExampleMeter_attributes() {
 			metric.WithAttributes(semconv.HTTPResponseStatusCode(statusCode)))
 	})
 }
+
+// You can define metrics which are disabled by default using the [WithOptIn] option.
+//
+// Here's how you might define a counter that is disabled by default.
+func ExampleMeter_withOptIn() {
+	var err error
+	itemsCounter, err := meter.Int64UpDownCounter(
+		"items.counter",
+		metric.WithDescription("Number of items."),
+		metric.WithUnit("{item}"),
+		metric.WithOptIn(),
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	// This increment is a no-op unless the user has explicitly enabled the
+	// metric using the SDK.
+	itemsCounter.Add(context.Background(), 1)
+}

metric/instrument.go

@@ -196,6 +196,85 @@
 // The unit u should be defined using the appropriate [UCUM](https://ucum.org) case-sensitive code.
 func WithUnit(u string) InstrumentOption { return unitOpt(u) }
 
+type optInOpt struct{}
+
+func (o optInOpt) applyFloat64Counter(c Float64CounterConfig) Float64CounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyFloat64UpDownCounter(c Float64UpDownCounterConfig) Float64UpDownCounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyFloat64Histogram(c Float64HistogramConfig) Float64HistogramConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyFloat64Gauge(c Float64GaugeConfig) Float64GaugeConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyFloat64ObservableCounter(c Float64ObservableCounterConfig) Float64ObservableCounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyFloat64ObservableUpDownCounter(
+	c Float64ObservableUpDownCounterConfig,
+) Float64ObservableUpDownCounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyFloat64ObservableGauge(c Float64ObservableGaugeConfig) Float64ObservableGaugeConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64Counter(c Int64CounterConfig) Int64CounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64UpDownCounter(c Int64UpDownCounterConfig) Int64UpDownCounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64Histogram(c Int64HistogramConfig) Int64HistogramConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64Gauge(c Int64GaugeConfig) Int64GaugeConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64ObservableCounter(c Int64ObservableCounterConfig) Int64ObservableCounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64ObservableUpDownCounter(
+	c Int64ObservableUpDownCounterConfig,
+) Int64ObservableUpDownCounterConfig {
+	c.optIn = true
+	return c
+}
+
+func (o optInOpt) applyInt64ObservableGauge(c Int64ObservableGaugeConfig) Int64ObservableGaugeConfig {
+	c.optIn = true
+	return c
+}
+
+// WithOptIn sets the instrument to be disabled by default.
+func WithOptIn() InstrumentOption { return optInOpt{} }
+
 // WithExplicitBucketBoundaries sets the instrument explicit bucket boundaries.
 //
 // This option is considered "advisory", and may be ignored by API implementations.