Fix type conversion handling in convertToType function

gonull.go

@@ -99,22 +99,27 @@ func zeroValue[T any]() T {
 
 // convertToType is a helper function that attempts to convert the given value to type T.
 // This function is used by Scan to properly handle value conversion, ensuring that Nullable values are always of the correct type.
+// ErrUnsupportedConversion is returned when a conversion cannot be made to the generic type T.
 func convertToType[T any](value interface{}) (T, error) {
-	switch v := value.(type) {
-	case T:
-		return v, nil
-	case int64:
-		// This case handles the situation when the input value is of type int64.
-		// It attempts to convert the int64 value to the target numeric type T if possible.
-		// If the conversion is successful, it returns the converted value of type T and a nil error.
-		// If the conversion is not possible, the function will continue to the next case (return an error).
-		switch t := reflect.Zero(reflect.TypeOf((*T)(nil)).Elem()).Interface().(type) {
-		case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
-			if reflect.TypeOf(t).ConvertibleTo(reflect.TypeOf((*T)(nil)).Elem()) {
-				return reflect.ValueOf(value).Convert(reflect.TypeOf((*T)(nil)).Elem()).Interface().(T), nil
-			}
+	var zero T
+	if value == nil {
+		return zero, nil
+	}
+
+	if reflect.TypeOf(value) == reflect.TypeOf(zero) {
+		return value.(T), nil
+	}
+
+	// Check if the value is a numeric type and if T is also a numeric type.
+	valueType := reflect.TypeOf(value)
+	targetType := reflect.TypeOf(zero)
+	if valueType.Kind() >= reflect.Int && valueType.Kind() <= reflect.Float64 &&
+		targetType.Kind() >= reflect.Int && targetType.Kind() <= reflect.Float64 {
+		if valueType.ConvertibleTo(targetType) {
+			convertedValue := reflect.ValueOf(value).Convert(targetType)
+			return convertedValue.Interface().(T), nil
 		}
 	}
-	var zero T
+
 	return zero, ErrUnsupportedConversion
 }

gonull_test.go

@@ -276,11 +276,8 @@ func TestNullableScanWithCustomEnum(t *testing.T) {
 	model := TestModel{ID: 1, Field: gonull.NewNullable(TestEnumA)}
 
 	err := model.Field.Scan(sqlReturnedValue)
-	if err != nil {
-		assert.Error(t, err, "Scan failed with unsupported type conversion")
-	} else {
-		assert.Equal(t, TestEnumA, model.Field.Val, "Scanned value does not match expected enum value")
-	}
+	assert.NoError(t, err, "Scan failed with unsupported type conversion")
+	assert.Equal(t, TestEnumA, model.Field.Val, "Scanned value does not match expected enum value")
 
 }