Remove error from Future Set method

Author: cschleiden

internal/sync/future.go

@@ -1,9 +1,5 @@
 package sync
 
-import (
-	"errors"
-)
-
 type Future[T any] interface {
 	// Get returns the value if set, blocks otherwise
 	Get(ctx Context) (T, error)
@@ -12,8 +8,10 @@ type Future[T any] interface {
 type SettableFuture[T any] interface {
 	Future[T]
 
-	// Set stores the value
-	Set(v T, err error) error
+	// Set stores the value and provided error
+	Set(v T, err error)
+
+	HasValue() bool
 }
 
 type FutureInternal[T any] interface {
@@ -32,16 +30,14 @@ type future[T any] struct {
 	err      error
 }
 
-func (f *future[T]) Set(v T, err error) error {
-	if f.hasValue {
-		return errors.New("future already set")
-	}
-
+func (f *future[T]) Set(v T, err error) {
 	f.v = v
 	f.err = err
 	f.hasValue = true
+}
 
-	return nil
+func (f *future[T]) HasValue() bool {
+	return f.hasValue
 }
 
 func (f *future[T]) Get(ctx Context) (T, error) {

internal/sync/future_test.go

@@ -22,16 +22,6 @@ func Test_FutureYields(t *testing.T) {
 	require.True(t, c.Blocked())
 }
 
-func Test_FutureSetErrorsWhenSetTwice(t *testing.T) {
-	f := NewFuture[int]()
-
-	err := f.Set(42, nil)
-	require.NoError(t, err)
-
-	err = f.Set(42, nil)
-	require.Error(t, err)
-}
-
 func Test_FutureSetUnblocks(t *testing.T) {
 	f := NewFuture[int]()
 

internal/workflowstate/workflowstate.go

@@ -1,6 +1,7 @@
 package workflowstate
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/benbjohnson/clock"
@@ -18,19 +19,25 @@ var workflowCtxKey key
 
 type DecodingSettable func(v payload.Payload, err error) error
 
-// Use this to track futures for the workflow state
+// Use this to track futures for the workflow state. It's required to map the generic Future interface
+// to a type without type parameters.
 func AsDecodingSettable[T any](f sync.SettableFuture[T]) DecodingSettable {
 	return func(v payload.Payload, err error) error {
-		var ferr error
+		if f.HasValue() {
+			return fmt.Errorf("future already has value")
+		}
+
 		if v != nil {
 			var t T
-			converter.DefaultConverter.From(v, &t)
-			ferr = f.Set(t, err)
+			if err := converter.DefaultConverter.From(v, &t); err != nil {
+				return fmt.Errorf("failed to decode future: %v", err)
+			}
+			f.Set(t, err)
 		} else {
-			ferr = f.Set(*new(T), err)
+			f.Set(*new(T), err)
 		}
 
-		return ferr
+		return nil
 	}
 }