diff --git a/descriptor.go b/descriptor.go
index 55c7983..da00118 100644
--- a/descriptor.go
+++ b/descriptor.go
@@ -97,6 +97,8 @@ type (
 	DefaultValue struct {
 		Value interface{}
 	}
+
+	ValueGenerator func(i interface{}) (object interface{}, ok bool)
 )
 
 var Root = RootAsPath{}
@@ -265,6 +267,11 @@ func (dv DefaultValue) ExtractObject(interface{}) (object interface{}, ok bool)
 	return dv.Value, true
 }
 
+func (vg ValueGenerator) ExtractObject(data interface{}) (object interface{}, ok bool) {
+	object, ok = vg(data)
+	return
+}
+
 func (vs ValueSources) ExtractObject(data interface{}) (object interface{}, ok bool) {
 	for _, valueSource := range vs {
 		if valueSource == nil {