check interface implement for metric (#38)

Author: thinkerou

api/metric/api.go

@@ -20,17 +20,6 @@ import (
 	"github.com/open-telemetry/opentelemetry-go/api/unit"
 )
 
-type Metric interface {
-	Measure() core.Measure
-
-	DefinitionID() core.EventID
-
-	Type() MetricType
-	Fields() []core.Key
-	Err() error
-
-	base() *baseMetric
-}
 type MetricType int
 
 const (
@@ -45,6 +34,18 @@ const (
 	DerivedCumulativeFloat64
 )
 
+type Metric interface {
+	Measure() core.Measure
+
+	DefinitionID() core.EventID
+
+	Type() MetricType
+	Fields() []core.Key
+	Err() error
+
+	base() *baseMetric
+}
+
 type Option func(*baseMetric, *[]tag.Option)
 
 // WithDescription applies provided description.

api/metric/common.go

@@ -36,6 +36,8 @@ type baseEntry struct {
 	eventID core.EventID
 }
 
+var _ Metric = (*baseMetric)(nil)
+
 func initBaseMetric(name string, mtype MetricType, opts []Option, init Metric) Metric {
 	var tagOpts []tag.Option
 	bm := init.base()

api/metric/registry.go

@@ -44,6 +44,8 @@ type registry struct {
 	nameType sync.Map // map[string]Metric
 }
 
+var _ Registry = (*registry)(nil)
+
 var (
 	registryLock   sync.Mutex
 	registryGlobal Registry = &registry{}