vm: make Iterator interface public

There is nothing wrong with iterators being implemented in other parts
of code (e.g. Storage.Find). In this case type assertions can
prevent bugs at compile-time.

pkg/core/storage_find.go

@@ -11,6 +11,8 @@ type storageWrapper struct {
 	finished   bool
 }
 
+var _ vm.Iterator = (*storageWrapper)(nil)
+
 // newStorageIterator returns new storage iterator from the `next()` callback.
 func newStorageIterator(next dao.StorageIteratorFunc) *storageWrapper {
 	return &storageWrapper{
@@ -18,7 +20,7 @@ func newStorageIterator(next dao.StorageIteratorFunc) *storageWrapper {
 	}
 }
 
-// Next implements iterator interface.
+// Next implements vm.Iterator interface.
 func (s *storageWrapper) Next() bool {
 	if s.finished {
 		return false
@@ -33,12 +35,12 @@ func (s *storageWrapper) Next() bool {
 	return true
 }
 
-// Value implements iterator interface.
+// Value implements vm.Iterator interface.
 func (s *storageWrapper) Value() vm.StackItem {
 	return s.value
 }
 
-// Key implements iterator interface.
+// Key implements vm.Iterator interface.
 func (s *storageWrapper) Key() vm.StackItem {
 	return s.key
 }

pkg/vm/interop.go

@@ -205,9 +205,9 @@ func NewMapIterator(m *MapItem) *InteropItem {
 // IteratorConcat handles syscall Neo.Iterator.Concat.
 func IteratorConcat(v *VM) error {
 	iop1 := v.Estack().Pop().Interop()
-	iter1 := iop1.value.(iterator)
+	iter1 := iop1.value.(Iterator)
 	iop2 := v.Estack().Pop().Interop()
-	iter2 := iop2.value.(iterator)
+	iter2 := iop2.value.(Iterator)
 
 	v.Estack().Push(&Element{value: NewInteropItem(
 		&concatIter{
@@ -222,7 +222,7 @@ func IteratorConcat(v *VM) error {
 // IteratorKey handles syscall Neo.Iterator.Key.
 func IteratorKey(v *VM) error {
 	iop := v.estack.Pop().Interop()
-	iter := iop.value.(iterator)
+	iter := iop.value.(Iterator)
 	v.Estack().Push(&Element{value: iter.Key()})
 
 	return nil
@@ -231,7 +231,7 @@ func IteratorKey(v *VM) error {
 // IteratorKeys handles syscall Neo.Iterator.Keys.
 func IteratorKeys(v *VM) error {
 	iop := v.estack.Pop().Interop()
-	iter := iop.value.(iterator)
+	iter := iop.value.(Iterator)
 	v.Estack().Push(&Element{value: NewInteropItem(
 		&keysWrapper{iter},
 	)})
@@ -242,7 +242,7 @@ func IteratorKeys(v *VM) error {
 // IteratorValues handles syscall Neo.Iterator.Values.
 func IteratorValues(v *VM) error {
 	iop := v.estack.Pop().Interop()
-	iter := iop.value.(iterator)
+	iter := iop.value.(Iterator)
 	v.Estack().Push(&Element{value: NewInteropItem(
 		&valuesWrapper{iter},
 	)})

pkg/vm/interop_iterators.go

@@ -18,7 +18,8 @@ type (
 )
 
 type (
-	iterator interface {
+	// Iterator defined public interface for VM's iterator type.
+	Iterator interface {
 		enumerator
 		Key() StackItem
 	}
@@ -29,16 +30,16 @@ type (
 	}
 
 	concatIter struct {
-		current iterator
-		second  iterator
+		current Iterator
+		second  Iterator
 	}
 
 	keysWrapper struct {
-		iter iterator
+		iter Iterator
 	}
 
 	valuesWrapper struct {
-		iter iterator
+		iter Iterator
 	}
 )