renames, lint fixes, and an error d'oh

go-runtime/ftl/singleton.go

@@ -5,25 +5,23 @@ import (
 	"sync"
 )
 
-type InputLambda[T any] func(context.Context) (T, error)
-
-type SingletonConstructor[T any] struct {
-	Fn   InputLambda[T]
-	Out  T
-	Once sync.Once
+type SingletonHandle[T any] struct {
+	fn   func(context.Context) (T, error)
+	out  T
+	once *sync.Once
 }
 
-func (sf *SingletonConstructor[T]) Get(ctx context.Context) T {
-	sf.Once.Do(func() {
-		t, err := sf.Fn(ctx)
+func (sh *SingletonHandle[T]) Get(ctx context.Context) T {
+	sh.once.Do(func() {
+		t, err := sh.fn(ctx)
 		if err != nil {
 			panic(err)
 		}
-		sf.Out = t
+		sh.out = t
 	})
-	return sf.Out
+	return sh.out
 }
 
-func Singleton[T any](fn InputLambda[T]) SingletonConstructor[T] {
-    return SingletonConstructor[T]{Fn: fn}
+func Singleton[T any](fn func(context.Context) (T, error)) SingletonHandle[T] {
+	return SingletonHandle[T]{fn: fn, once: &sync.Once{}}
 }

go-runtime/ftl/singleton_test.go

@@ -2,6 +2,7 @@ package ftl
 
 import (
 	"context"
+	"fmt"
 	"testing"
 
 	"github.com/alecthomas/assert/v2"
@@ -12,7 +13,7 @@ func TestSingletonBaseCase(t *testing.T) {
 
 	ctx := context.Background()
 	once := Singleton[string](func(ctx context.Context) (string, error) {
-		incrementer += 1
+		incrementer++
 		return "only once", nil
 	})
 
@@ -24,8 +25,7 @@ func TestSingletonBaseCase(t *testing.T) {
 func TestSingletonPanic(t *testing.T) {
 	ctx := context.Background()
 	once := Singleton[string](func(ctx context.Context) (string, error) {
-		panic("test panic")
-		return "only once", nil
+		return "", fmt.Errorf("test error")
 	})
 	assert.Panics(t, func() {
 		once.Get(ctx)