Add extra OnPlace/OnProfile/OnRelationship/OnTombstone functions

place.go

@@ -228,3 +228,13 @@ func ToPlace(it Item) (*Place, error) {
 	}
 	return nil, fmt.Errorf("unable to convert %q", it.GetType())
 }
+
+type withPlaceFn func (*Place) error
+
+func OnPlace(it Item, fn withPlaceFn) error {
+	ob, err  := ToPlace(it)
+	if err != nil {
+		return err
+	}
+	return fn(ob)
+}

profile.go

@@ -196,3 +196,13 @@ func ToProfile(it Item) (*Profile, error) {
 	}
 	return nil, fmt.Errorf("unable to convert %q", it.GetType())
 }
+
+type withProfileFn func (*Profile) error
+
+func OnProfile(it Item, fn withProfileFn) error {
+	ob, err  := ToProfile(it)
+	if err != nil {
+		return err
+	}
+	return fn(ob)
+}

relationship.go

@@ -211,3 +211,13 @@ func ToRelationship(it Item) (*Relationship, error) {
 	}
 	return nil, fmt.Errorf("unable to convert %q", it.GetType())
 }
+
+type withRelationshipFn func (*Relationship) error
+
+func OnRelationship(it Item, fn withRelationshipFn) error {
+	ob, err  := ToRelationship(it)
+	if err != nil {
+		return err
+	}
+	return fn(ob)
+}

tombstone.go

@@ -203,3 +203,13 @@ func ToTombstone(it Item) (*Tombstone, error) {
 	}
 	return nil, fmt.Errorf("unable to convert %q", it.GetType())
 }
+
+type withTombstoneFn func (*Tombstone) error
+
+func OnTombstone(it Item, fn withTombstoneFn) error {
+	ob, err  := ToTombstone(it)
+	if err != nil {
+		return err
+	}
+	return fn(ob)
+}