even more refactoring

grain-pool.go

@@ -26,7 +26,7 @@ var (
 )
 
 type GrainPool interface {
-	Process(id CartId, mutations ...interface{}) (*CartGrain, error)
+	Apply(id CartId, mutation interface{}) (*CartGrain, error)
 	Get(id CartId) (*CartGrain, error)
 }
 
@@ -142,18 +142,12 @@ func (p *GrainLocalPool) GetGrain(id CartId) (*CartGrain, error) {
 	return grain, err
 }
 
-func (p *GrainLocalPool) Process(id CartId, mutations ...interface{}) (*CartGrain, error) {
+func (p *GrainLocalPool) Apply(id CartId, mutation interface{}) (*CartGrain, error) {
 	grain, err := p.GetGrain(id)
-	var result *CartGrain
-	if err == nil && grain != nil {
-		for _, m := range mutations {
-			result, err = grain.Apply(m, false)
-			if err != nil {
-				break
-			}
-		}
+	if err != nil || grain == nil {
+		return nil, err
 	}
-	return result, err
+	return grain.Apply(mutation, false)
 }
 
 func (p *GrainLocalPool) Get(id CartId) (*CartGrain, error) {