1 files changed, 25 insertions, 9 deletions
diff --git a/storage/memory/storage.go b/storage/memory/storage.go
index 2380fed..927ec41 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,
@@ -29,17 +30,17 @@ type Storage struct {
 // NewStorage returns a new Storage base on memory
 func NewStorage() *Storage {
 	return &Storage{
-		ReferenceStorage: make(ReferenceStorage, 0),
+		ReferenceStorage: make(ReferenceStorage),
 		ConfigStorage:    ConfigStorage{},
 		ShallowStorage:   ShallowStorage{},
 		ObjectStorage: ObjectStorage{
-			Objects: make(map[plumbing.Hash]plumbing.EncodedObject, 0),
-			Commits: make(map[plumbing.Hash]plumbing.EncodedObject, 0),
-			Trees:   make(map[plumbing.Hash]plumbing.EncodedObject, 0),
-			Blobs:   make(map[plumbing.Hash]plumbing.EncodedObject, 0),
-			Tags:    make(map[plumbing.Hash]plumbing.EncodedObject, 0),
+			Objects: make(map[plumbing.Hash]plumbing.EncodedObject),
+			Commits: make(map[plumbing.Hash]plumbing.EncodedObject),
+			Trees:   make(map[plumbing.Hash]plumbing.EncodedObject),
+			Blobs:   make(map[plumbing.Hash]plumbing.EncodedObject),
+			Tags:    make(map[plumbing.Hash]plumbing.EncodedObject),
 		},
-		ModuleStorage: make(ModuleStorage, 0),
+		ModuleStorage: make(ModuleStorage),
 	}
 }
 
@@ -151,7 +152,7 @@ func flattenObjectMap(m map[plumbing.Hash]plumbing.EncodedObject) []plumbing.Enc
 func (o *ObjectStorage) Begin() storer.Transaction {
 	return &TxObjectStorage{
 		Storage: o,
-		Objects: make(map[plumbing.Hash]plumbing.EncodedObject, 0),
+		Objects: make(map[plumbing.Hash]plumbing.EncodedObject),
 	}
 }
 
@@ -188,7 +189,7 @@ func (tx *TxObjectStorage) Commit() error {
 }
 
 func (tx *TxObjectStorage) Rollback() error {
-	tx.Objects = make(map[plumbing.Hash]plumbing.EncodedObject, 0)
+	tx.Objects = make(map[plumbing.Hash]plumbing.EncodedObject)
 	return nil
 }
 
@@ -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 {