Set the ItemTyperFunc when doing UnmarshalJSON

activity.go

@@ -1532,6 +1532,9 @@ func (u *Update) UnmarshalJSON(data []byte) error {
 
 // UnmarshalJSON
 func (c *Create) UnmarshalJSON(data []byte) error {
+	if ItemTyperFunc == nil {
+		ItemTyperFunc = JSONGetItemByType
+	}
 	a := Activity(*c)
 	err := a.UnmarshalJSON(data)
 

collections.go

@@ -203,6 +203,9 @@ func (o OrderedCollection) IsObject() bool {
 
 // UnmarshalJSON
 func (o *OrderedCollection) UnmarshalJSON(data []byte) error {
+	if ItemTyperFunc == nil {
+		ItemTyperFunc = JSONGetItemByType
+	}
 	o.Parent.UnmarshalJSON(data)
 
 	o.TotalItems = uint(JSONGetInt(data, "totalItems"))

link.go

@@ -116,6 +116,9 @@ func (m Mention) GetType() ActivityVocabularyType {
 
 // UnmarshalJSON
 func (l *Link) UnmarshalJSON(data []byte) error {
+	if ItemTyperFunc == nil {
+		ItemTyperFunc = JSONGetItemByType
+	}
 	l.ID = JSONGetObjectID(data)
 	l.Type = JSONGetType(data)
 	l.MediaType = JSONGetMimeType(data)

object.go

@@ -531,6 +531,9 @@ func (c *MimeType) UnmarshalJSON(data []byte) error {
 
 // UnmarshalJSON
 func (o *Object) UnmarshalJSON(data []byte) error {
+	if ItemTyperFunc == nil {
+		ItemTyperFunc = JSONGetItemByType
+	}
 	o.ID = JSONGetObjectID(data)
 	o.Type = JSONGetType(data)
 	o.Name = JSONGetNaturalLanguageField(data, "name")

unmarshalling.go

@@ -19,7 +19,7 @@ var (
 
 // ItemTyperFunc will return an instance of a struct that implements activitystreams.Item
 // The default for this package is JSONGetItemByType but can be overwritten
-var ItemTyperFunc TyperFunction = JSONGetItemByType
+var ItemTyperFunc TyperFunction
 
 // TyperFunction is the type of the function which returns an activitystreams.Item struct instance
 // for a specific ActivityVocabularyType
@@ -234,6 +234,9 @@ func JSONGetIRI(data []byte, prop string) IRI {
 // UnmarshalJSON tries to detect the type of the object in the json data and then outputs a matching
 // ActivityStreams object, if possible
 func UnmarshalJSON(data []byte) (Item, error) {
+	if ItemTyperFunc == nil {
+		ItemTyperFunc = JSONGetItemByType
+	}
 	return JSONUnmarshalToItem(data), nil
 }