refine composer api a bit

composer.go

@@ -13,22 +13,8 @@ type LabelComposer interface {
 	ToLabelsString() string
 }
 
-// labelComposerMarker is a marker interface for enforcing type-safety of StructLabelComposer.
-// Interface is private so it's only be used via StructLabelComposer implementation.
-// This is made for safety reasons, so it's not allowed to pass a random struct to NameCompose() function.
-type labelComposerMarker interface {
-	labelComposerMarker()
-}
-
-// StructLabelComposer MUST be embedded in any struct that serves as a label composer.
-// Embedding is required even if you provide custom implementation of LabelComposer (ToLabelsString() method)
-type StructLabelComposer struct{}
-
-func (s StructLabelComposer) labelComposerMarker() { panic("should never happen") }
-
 // NameCompose returns a valid full metric name, composed of a metric name + stringified labels
-// It will first try to use custom LabelComposer implementation (if any)
-// then fallback to slow reflection-based implementation.
+// It accepts a valid LabelComposer interface, which is used to compose labels string.
 //
 // The NameCompose can be called for further GetOrCreateCounter/etc func:
 //
@@ -37,19 +23,46 @@ func (s StructLabelComposer) labelComposerMarker() { panic("should never happen"
 //	  Status: "active",
 //	  Flag:   false,
 //	})).Inc()
-func NameCompose(name string, lc labelComposerMarker) string {
+func NameCompose(name string, lc LabelComposer) string {
 	if lc == nil {
 		return name
 	}
 
-	// Implementing public LabelComposer means we must implement
-	// a custom ToLabelsString() that supposed to be fast.
-	if v, ok := lc.(LabelComposer); ok {
-		return name + v.ToLabelsString()
+	return name + lc.ToLabelsString()
+}
+
+//
+// Auto composer
+//
+
+// labelComposerAutoMarker is just a marker interface.
+// Interface is private so it's only be used via AutoLabelComposer implementation.
+// This is made for safety reasons, so it's not allowed to pass a random struct to NameCompose() function.
+type labelComposerAutoMarker interface {
+	autoComposeMarker()
+}
+
+// AutoLabelComposer MUST be embedded in any struct that serves as a label composer.
+// Embedding is required even if you provide custom implementation of LabelComposer (ToLabelsString() method)
+type AutoLabelComposer struct{}
+
+func (s AutoLabelComposer) autoComposeMarker() { panic("should never happen") }
+
+// NameComposeAuto returns a valid full metric name, composed of a metric name + stringified labels
+// It accepts a struct who embeds AutoLabelComposer so labels are generated from it.
+//
+// The NameComposeAuto can be called for further GetOrCreateCounter/etc func:
+//
+//	// `my_counter{status="active",flag="false"}`
+//	GetOrCreateCounter(NameComposeAuto("my_counter", MyLabels{
+//	  Status: "active",
+//	  Flag:   false,
+//	})).Inc()
+func NameComposeAuto(name string, lc labelComposerAutoMarker) string {
+	if lc == nil {
+		return name
 	}
 
-	// falling back to reflect-based implementation
-	// This is considered to be slow. Implement your own LabelComposer if it's an issue for you.
 	return name + reflectLabelCompose(lc)
 }
 
@@ -57,7 +70,7 @@ func NameCompose(name string, lc labelComposerMarker) string {
 // It will use only exported scalar fields, and will skip fields with the `-` tag.
 // By default, the snake_cased field name is used as the label name.
 // Label's name can be overridden by using the `labels` tag
-func reflectLabelCompose(lc labelComposerMarker) string {
+func reflectLabelCompose(lc labelComposerAutoMarker) string {
 	labelsStr := "{"
 
 	val := reflect.Indirect(reflect.ValueOf(lc))

composer_test.go

@@ -5,34 +5,11 @@ import (
 	"testing"
 )
 
-// MyLabelsSlow will be converted into {hello="world",enabled="true"}
-// via reflect implementation.
-// It's slow but completely automatic. You don't need to write any code
-type MyLabelsSlow struct {
-	StructLabelComposer
-
-	Status string
-	Flag   bool
-}
-
-func TestLabelComposeWithReflect(t *testing.T) {
-	want := `my_counter{status="active",flag="true"}`
-
-	got := NameCompose("my_counter", MyLabelsSlow{
-		Status: "active",
-		Flag:   true,
-	})
-
-	if got != want {
-		t.Fatalf("unexpected full name; got %q; want %q", got, want)
-	}
-}
-
 // MyLabelsFast will be converted into string
 // via custom implementation (Using ToLabelsString() method of LabelComposer interface)
 // It's fast but requires manual implementation.
 type MyLabelsFast struct {
-	StructLabelComposer
+	AutoLabelComposer
 	Status string
 	Flag   bool
 }
@@ -40,7 +17,7 @@ type MyLabelsFast struct {
 func (m *MyLabelsFast) ToLabelsString() string {
 	return "{" +
 		`status="` + m.Status + `",` +
-		`flag="` + fmt.Sprintf("%v", m.Flag) + `"` +
+		`flag="` + fmt.Sprintf("%t", m.Flag) + `"` +
 		"}"
 }
 
@@ -54,3 +31,26 @@ func TestLabelComposeWithoutReflect(t *testing.T) {
 		t.Fatalf("unexpected full name; got %q; want %q", got, want)
 	}
 }
+
+func TestLabelComposeWithReflect(t *testing.T) {
+	want := `my_counter{status="active",flag="true"}`
+
+	// MyLabelsSlow will be converted into {hello="world",enabled="true"}
+	// via reflect implementation.
+	// It's slow but completely automatic. You don't need to write any code
+	type MyLabelsAuto struct {
+		AutoLabelComposer
+
+		Status string
+		Flag   bool
+	}
+
+	got := NameComposeAuto("my_counter", MyLabelsAuto{
+		Status: "active",
+		Flag:   true,
+	})
+
+	if got != want {
+		t.Fatalf("unexpected full name; got %q; want %q", got, want)
+	}
+}