1 files changed, 16 insertions, 0 deletions
diff --git a/storage/memory/storage.go b/storage/memory/storage.go
index 2380fed..c9306ee 100644
--- a/storage/memory/storage.go
+++ b/storage/memory/storage.go
@@ -12,6 +12,7 @@ import (
 )
 
 var ErrUnsupportedObjectType = fmt.Errorf("unsupported object type")
+var ErrRefHasChanged = fmt.Errorf("reference has changed concurrently")
 
 // Storage is an implementation of git.Storer that stores data on memory, being
 // ephemeral. The use of this storage should be done in controlled envoriments,
@@ -202,6 +203,21 @@ func (r ReferenceStorage) SetReference(ref *plumbing.Reference) error {
 	return nil
 }
 
+func (r ReferenceStorage) CheckAndSetReference(ref, old *plumbing.Reference) error {
+	if ref == nil {
+		return nil
+	}
+
+	if old != nil {
+		tmp := r[ref.Name()]
+		if tmp != nil && tmp.Hash() != old.Hash() {
+			return ErrRefHasChanged
+		}
+	}
+	r[ref.Name()] = ref
+	return nil
+}
+
 func (r ReferenceStorage) Reference(n plumbing.ReferenceName) (*plumbing.Reference, error) {
 	ref, ok := r[n]
 	if !ok {