3 files changed, 13 insertions, 24 deletions
diff --git a/plumbing/storer/object.go b/plumbing/storer/object.go
index 3f41468..e793211 100644
--- a/plumbing/storer/object.go
+++ b/plumbing/storer/object.go
@@ -123,7 +123,7 @@ func (iter *EncodedObjectLookupIter) Next() (plumbing.EncodedObject, error) {
 }
 
 // ForEach call the cb function for each object contained on this iter until
-// an error happends or the end of the iter is reached. If ErrStop is sent
+// an error happens or the end of the iter is reached. If ErrStop is sent
 // the iteration is stop but no error is returned. The iterator is closed.
 func (iter *EncodedObjectLookupIter) ForEach(cb func(plumbing.EncodedObject) error) error {
 	return ForEachIterator(iter, cb)
@@ -168,7 +168,7 @@ func (iter *EncodedObjectSliceIter) Next() (plumbing.EncodedObject, error) {
 }
 
 // ForEach call the cb function for each object contained on this iter until
-// an error happends or the end of the iter is reached. If ErrStop is sent
+// an error happens or the end of the iter is reached. If ErrStop is sent
 // the iteration is stop but no error is returned. The iterator is closed.
 func (iter *EncodedObjectSliceIter) ForEach(cb func(plumbing.EncodedObject) error) error {
 	return ForEachIterator(iter, cb)
@@ -213,7 +213,7 @@ func (iter *MultiEncodedObjectIter) Next() (plumbing.EncodedObject, error) {
 }
 
 // ForEach call the cb function for each object contained on this iter until
-// an error happends or the end of the iter is reached. If ErrStop is sent
+// an error happens or the end of the iter is reached. If ErrStop is sent
 // the iteration is stop but no error is returned. The iterator is closed.
 func (iter *MultiEncodedObjectIter) ForEach(cb func(plumbing.EncodedObject) error) error {
 	return ForEachIterator(iter, cb)
diff --git a/plumbing/storer/reference.go b/plumbing/storer/reference.go
index 988c784..ae80a39 100644
--- a/plumbing/storer/reference.go
+++ b/plumbing/storer/reference.go
@@ -16,6 +16,11 @@ var ErrMaxResolveRecursion = errors.New("max. recursion level reached")
 // ReferenceStorer is a generic storage of references.
 type ReferenceStorer interface {
 	SetReference(*plumbing.Reference) error
+	// CheckAndSetReference sets the reference `new`, but if `old` is
+	// not `nil`, it first checks that the current stored value for
+	// `old.Name()` matches the given reference value in `old`.  If
+	// not, it returns an error and doesn't update `new`.
+	CheckAndSetReference(new, old *plumbing.Reference) error
 	Reference(plumbing.ReferenceName) (*plumbing.Reference, error)
 	IterReferences() (ReferenceIter, error)
 	RemoveReference(plumbing.ReferenceName) error
@@ -121,7 +126,7 @@ func (iter *ReferenceSliceIter) Next() (*plumbing.Reference, error) {
 }
 
 // ForEach call the cb function for each reference contained on this iter until
-// an error happends or the end of the iter is reached. If ErrStop is sent
+// an error happens or the end of the iter is reached. If ErrStop is sent
 // the iteration is stop but no error is returned. The iterator is closed.
 func (iter *ReferenceSliceIter) ForEach(cb func(*plumbing.Reference) error) error {
 	defer iter.Close()
diff --git a/plumbing/storer/reference_test.go b/plumbing/storer/reference_test.go
index 5738eef..490ec95 100644
--- a/plumbing/storer/reference_test.go
+++ b/plumbing/storer/reference_test.go
@@ -97,11 +97,7 @@ func (s *ReferenceSuite) TestReferenceFilteredIterNext(c *C) {
 	}
 
 	i := NewReferenceFilteredIter(func(r *plumbing.Reference) bool {
-		if r.Name() == "bar" {
-			return true
-		}
-
-		return false
+		return r.Name() == "bar"
 	}, NewReferenceSliceIter(slice))
 	foo, err := i.Next()
 	c.Assert(err, IsNil)
@@ -120,11 +116,7 @@ func (s *ReferenceSuite) TestReferenceFilteredIterForEach(c *C) {
 	}
 
 	i := NewReferenceFilteredIter(func(r *plumbing.Reference) bool {
-		if r.Name() == "bar" {
-			return true
-		}
-
-		return false
+		return r.Name() == "bar"
 	}, NewReferenceSliceIter(slice))
 	var count int
 	i.ForEach(func(r *plumbing.Reference) error {
@@ -143,11 +135,7 @@ func (s *ReferenceSuite) TestReferenceFilteredIterError(c *C) {
 	}
 
 	i := NewReferenceFilteredIter(func(r *plumbing.Reference) bool {
-		if r.Name() == "bar" {
-			return true
-		}
-
-		return false
+		return r.Name() == "bar"
 	}, NewReferenceSliceIter(slice))
 	var count int
 	exampleErr := errors.New("SOME ERROR")
@@ -172,11 +160,7 @@ func (s *ReferenceSuite) TestReferenceFilteredIterForEachStop(c *C) {
 	}
 
 	i := NewReferenceFilteredIter(func(r *plumbing.Reference) bool {
-		if r.Name() == "bar" {
-			return true
-		}
-
-		return false
+		return r.Name() == "bar"
 	}, NewReferenceSliceIter(slice))
 
 	var count int