move type name to a method on localFunctionDialect interface

functions/dialect.go

@@ -97,18 +97,6 @@ type mapAndSlice[V extensions.FunctionVariant] struct {
 	variantsSlice []V
 }
 
-func nameForInvocationType(invocationType interface{}) string {
-	switch invocationType.(type) {
-	case *LocalScalarFunctionVariant:
-		return "scalar function"
-	case *LocalAggregateFunctionVariant:
-		return "aggregate function"
-	case *LocalWindowFunctionVariant:
-		return "window function"
-	}
-	return "function"
-}
-
 // makeLocalFunctionVariantMapAndSlice creates a map of function names to their variants and a slice of all variants.
 // The map is indexed by both the SubstraitFunctionName and the LocalFunctionName
 // It returns
@@ -125,7 +113,7 @@ func makeLocalFunctionVariantMapAndSlice[T withID, V localFunctionVariant](
 		if _, nameAlreadyProcessed := variantsMap[LocalFunctionName(dfi.Name)]; nameAlreadyProcessed {
 			if _, ok := processedFunctions[dfi.ID]; !ok {
 				var invocationType V
-				return nil, fmt.Errorf("%w: no %s variant found for '%s'", substraitgo.ErrInvalidDialect, nameForInvocationType(invocationType), dfi.ID)
+				return nil, fmt.Errorf("%w: no %s function variant found for '%s'", substraitgo.ErrInvalidDialect, invocationType.InvocationTypeName(), dfi.ID)
 			}
 			continue
 		}
@@ -141,7 +129,7 @@ func makeLocalFunctionVariantMapAndSlice[T withID, V localFunctionVariant](
 		}
 		if _, ok := processedFunctions[dfi.ID]; !ok {
 			var invocationType V
-			return nil, fmt.Errorf("%w: no %s variant found for '%s'", substraitgo.ErrInvalidDialect, nameForInvocationType(invocationType), dfi.ID)
+			return nil, fmt.Errorf("%w: no %s function variant found for '%s'", substraitgo.ErrInvalidDialect, invocationType.InvocationTypeName(), dfi.ID)
 		}
 		if len(localVariantArray) > 0 {
 			addToSliceMap(variantsMap, SubstraitFunctionName(dfi.Name), localVariantArray)

functions/registries.go

@@ -111,6 +111,7 @@ type localFunctionVariant interface {
 	LocalName() string
 	Notation() FunctionNotation
 	IsOptionSupported(name string, value string) bool
+	InvocationTypeName() string
 }
 
 type LocalFunctionVariant struct {
@@ -149,20 +150,32 @@ type LocalScalarFunctionVariant struct {
 
 var _ extensions.FunctionVariant = &LocalScalarFunctionVariant{}
 
+func (l *LocalScalarFunctionVariant) InvocationTypeName() string {
+	return "scalar"
+}
+
 type LocalAggregateFunctionVariant struct {
 	extensions.AggregateFunctionVariant
 	LocalFunctionVariant
 }
 
 var _ extensions.FunctionVariant = &LocalAggregateFunctionVariant{}
 
+func (l *LocalAggregateFunctionVariant) InvocationTypeName() string {
+	return "aggregate"
+}
+
 type LocalWindowFunctionVariant struct {
 	extensions.WindowFunctionVariant
 	LocalFunctionVariant
 }
 
 var _ extensions.FunctionVariant = &LocalWindowFunctionVariant{}
 
+func (l *LocalWindowFunctionVariant) InvocationTypeName() string {
+	return "window"
+}
+
 func newLocalScalarFunctionVariant(sf *extensions.ScalarFunctionVariant, dfi *dialectFunctionInfo) *LocalScalarFunctionVariant {
 	return &LocalScalarFunctionVariant{
 		ScalarFunctionVariant: *sf,