.

go/zodb/btree/btree.go

@@ -178,14 +178,16 @@ func (b *Bucket) get(key KEY) (interface{}, bool) {
 //
 // In the above, key[i] means self->data[i].key, and similarly for child[i].
 
+type btreeState BTree // hide state methods from public API
+
 // DropState implements zodb.Stateful.
-func (t *BTree) DropState() {
+func (t *btreeState) DropState() {
 	t.firstbucket = nil
 	t.data = nil
 }
 
 // PySetState implements zodb.PyStateful to set btree data from pystate.
-func (bt *BTree) PySetState(pystate interface{}) error {
+func (bt *btreeState) PySetState(pystate interface{}) error {
 	// empty btree
 	if _, ok := pystate.(pickle.None); ok {
 		bt.firstbucket = nil
@@ -201,7 +203,7 @@ func (bt *BTree) PySetState(pystate interface{}) error {
 	// btree with 1 child bucket without oid
 	if len(t) == 1 {
 		bucket := &Bucket{PyPersistent: nil /* FIXME */}
-		err := bucket.PySetState(t[0])
+		err := (*bucketState)(bucket).PySetState(t[0])
 		if err != nil {
 			// XXX
 		}
@@ -265,15 +267,17 @@ func (bt *BTree) PySetState(pystate interface{}) error {
 //	     <self->next iff non-NULL>
 //	)
 
+type bucketState Bucket // hide state methods from public API
+
 // DropState implements Stateful to discard bucket state.
-func (b *Bucket) DropState() {
+func (b *bucketState) DropState() {
 	b.next = nil
 	b.keys = nil
 	b.values = nil
 }
 
 // PySetState implements PyStateful to set bucket data from pystate.
-func (b *Bucket) PySetState(pystate interface{}) error {
+func (b *bucketState) PySetState(pystate interface{}) error {
 	t, ok := pystate.(pickle.Tuple)
 	if !ok || !(1 <= len(t) && len(t) <= 2) {
 		// XXX complain
@@ -318,6 +322,7 @@ func (b *Bucket) PySetState(pystate interface{}) error {
 // ---- register classes to ZODB ----
 
 func init() {
-	zodb.RegisterClass("zodb.BTree.LOBucket", reflect.TypeOf(Bucket{}))
-	zodb.RegisterClass("zodb.BTree.LOBtree",  reflect.TypeOf(BTree{}))
+	t := reflect.TypeOf
+	zodb.RegisterClass("zodb.BTree.LOBucket", t(Bucket{}), t(bucketState{}))
+	zodb.RegisterClass("zodb.BTree.LOBtree",  t(BTree{}),  t(btreeState{}))
 }

go/zodb/connection.go

@@ -110,8 +110,8 @@ type LiveCacheControl interface {
 
 // ---- class <-> type; new ghost ----
 
-var class2Type = make(map[string]reflect.Type) // {} class -> type
-var type2Class = make(map[reflect.Type]string) // {} type -> class
+var class2Type = make(map[string]reflect.Type) // {} class -> (type, stateType)
+var type2Class = make(map[reflect.Type]string) // {} type -> (class, stateType)
 
 // zclassOf returns ZODB class of a Go object.
 //
@@ -128,11 +128,17 @@ var rPyStateful  = reflect.TypeOf((*PyStateful)(nil)).Elem()  // typeof(PyStatef
 
 // RegisterClass registers ZODB class to correspond to Go type.
 //
-// type must embed IPersistent.
-// *type must implement IPersistent, Ghostable and either Stateful or PyStateful.
+// typ must embed IPersistent; *typ must implement IPersistent.
+//
+// typ must be convertible to stateType; stateType must implement Ghostable and
+// either Stateful or PyStateful(*)
 //
 // Must be called from global init().
-func RegisterClass(class string, typ reflect.Type) {
+//
+// (*) the rationale for stateType coming separately is that this way for
+// application types it is possible not to expose Ghostable and Stateful
+// methods in their public API.
+func RegisterClass(class string, typ, stateType reflect.Type) {
 	badf := func(format string, argv ...interface{}) {
 		msg := fmt.Sprintf(format, argv...)
 		panic(fmt.Sprintf("zodb: register class (%q, %q): %s", class, typ, msg))
@@ -146,6 +152,8 @@ func RegisterClass(class string, typ reflect.Type) {
 	}
 
 	// typ must have IPersistent embedded
+	// TODO later change to directly embedding non-pointer Persistent | PyPersistent
+	// (optimize memory + less allocation)
 	basef, ok := typ.FieldByName("IPersistent")
 	if !(ok && basef.Anonymous && basef.Type == rIPersistent) {
 		badf("type does not embed IPersistent")