5 files changed, 30 insertions, 10 deletions

diff --git a/blob.go b/blob.go
index 5235597..227e014 100644
--- a/blob.go
+++ b/blob.go
@@ -20,6 +20,10 @@ type Blob struct {
 	cast_ptr *C.git_blob
 }
 
+func (b *Blob) AsObject() *Object {
+	return &b.Object
+}
+
 func (v *Blob) Size() int64 {
 	ret := int64(C.git_blob_rawsize(v.cast_ptr))
 	runtime.KeepAlive(v)
diff --git a/commit.go b/commit.go
index 5aa5f25..223b093 100644
--- a/commit.go
+++ b/commit.go
@@ -18,6 +18,10 @@ type Commit struct {
 	cast_ptr *C.git_commit
 }
 
+func (c *Commit) AsObject() *Object {
+	return &c.Object
+}
+
 func (c *Commit) Message() string {
 	ret := C.GoString(C.git_commit_message(c.cast_ptr))
 	runtime.KeepAlive(c)
diff --git a/object.go b/object.go
index f4f1b3e..5505e35 100644
--- a/object.go
+++ b/object.go
@@ -26,6 +26,11 @@ type Object struct {
 	repo *Repository
 }
 
+// Objecter lets us accept any kind of Git object in functions.
+type Objecter interface {
+	AsObject() *Object
+}
+
 func (t ObjectType) String() string {
 	switch t {
 	case ObjectAny:
diff --git a/tag.go b/tag.go
index a58b090..4debdb7 100644
--- a/tag.go
+++ b/tag.go
@@ -17,6 +17,10 @@ type Tag struct {
 	cast_ptr *C.git_tag
 }
 
+func (t *Tag) AsObject() *Object {
+	return &t.Object
+}
+
 func (t Tag) Message() string {
 	ret := C.GoString(C.git_tag_message(t.cast_ptr))
 	runtime.KeepAlive(t)
@@ -63,8 +67,7 @@ type TagsCollection struct {
 	repo *Repository
 }
 
-func (c *TagsCollection) Create(
-	name string, commit *Commit, tagger *Signature, message string) (*Oid, error) {
+func (c *TagsCollection) Create(name string, obj Objecter, tagger *Signature, message string) (*Oid, error) {
 
 	oid := new(Oid)
 
@@ -80,13 +83,13 @@ func (c *TagsCollection) Create(
 	}
 	defer C.git_signature_free(taggerSig)
 
-	ctarget := commit.ptr
-
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	ret := C.git_tag_create(oid.toC(), c.repo.ptr, cname, ctarget, taggerSig, cmessage, 0)
+	o := obj.AsObject()
+	ret := C.git_tag_create(oid.toC(), c.repo.ptr, cname, o.ptr, taggerSig, cmessage, 0)
 	runtime.KeepAlive(c)
+	runtime.KeepAlive(obj)
 	if ret < 0 {
 		return nil, MakeGitError(ret)
 	}
@@ -110,7 +113,7 @@ func (c *TagsCollection) Remove(name string) error {
 	return nil
 }
 
-// CreateLightweight creates a new lightweight tag pointing to a commit
+// CreateLightweight creates a new lightweight tag pointing to an object
 // and returns the id of the target object.
 //
 // The name of the tag is validated for consistency (see git_tag_create() for the rules
@@ -122,20 +125,20 @@ func (c *TagsCollection) Remove(name string) error {
 // The created tag is a simple reference and can be queried using
 // repo.References.Lookup("refs/tags/<name>"). The name of the tag (eg "v1.0.0")
 // is queried with ref.Shorthand().
-func (c *TagsCollection) CreateLightweight(name string, commit *Commit, force bool) (*Oid, error) {
+func (c *TagsCollection) CreateLightweight(name string, obj Objecter, force bool) (*Oid, error) {
 
 	oid := new(Oid)
 
 	cname := C.CString(name)
 	defer C.free(unsafe.Pointer(cname))
 
-	ctarget := commit.ptr
-
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	err := C.git_tag_create_lightweight(oid.toC(), c.repo.ptr, cname, ctarget, cbool(force))
+	o := obj.AsObject()
+	err := C.git_tag_create_lightweight(oid.toC(), c.repo.ptr, cname, o.ptr, cbool(force))
 	runtime.KeepAlive(c)
+	runtime.KeepAlive(obj)
 	if err < 0 {
 		return nil, MakeGitError(err)
 	}
diff --git a/tree.go b/tree.go
index f5cbd78..ee14ec5 100644
--- a/tree.go
+++ b/tree.go
@@ -27,6 +27,10 @@ type Tree struct {
 	cast_ptr *C.git_tree
 }
 
+func (t *Tree) AsObject() *Object {
+	return &t.Object
+}
+
 type TreeEntry struct {
 	Name     string
 	Id       *Oid