Take 2 on polymorphism

blob.go

@@ -7,17 +7,25 @@ package git
 */
 import "C"
 import (
-	"runtime"
 	"unsafe"
+	"runtime"
 )
 
 type Blob struct {
-	ptr *C.git_object
+	ptr *C.git_blob
 }
 
-func (v *Blob) Free() {
-	runtime.SetFinalizer(v, nil)
-	C.git_object_free(v.ptr)
+func (o *Blob) Id() *Oid {
+	return newOidFromC(C.git_blob_id(o.ptr))
+}
+
+func (o *Blob) Type() ObjectType {
+	return OBJ_BLOB
+}
+
+func (o *Blob) Free() {
+	runtime.SetFinalizer(o, nil)
+	C.git_blob_free(o.ptr)
 }
 
 func (v *Blob) Size() int64 {

commit.go

@@ -19,8 +19,17 @@ type Commit struct {
 	ptr *C.git_commit
 }
 
-func (c *Commit) Id() *Oid {
-	return newOidFromC(C.git_commit_id(c.ptr))
+func (o *Commit) Id() *Oid {
+	return newOidFromC(C.git_commit_id(o.ptr))
+}
+
+func (o *Commit) Type() ObjectType {
+	return OBJ_COMMIT
+}
+
+func (o *Commit) Free() {
+	runtime.SetFinalizer(o, nil)
+	C.git_commit_free(o.ptr)
 }
 
 func (c *Commit) Message() string {
@@ -28,15 +37,14 @@ func (c *Commit) Message() string {
 }
 
 func (c *Commit) Tree() (*Tree, error) {
-	tree := new(Tree)
+	var ptr *C.git_object
 
-	err := C.git_commit_tree(&tree.ptr, c.ptr)
+	err := C.git_commit_tree(&ptr, c.ptr)
 	if err < 0 {
 		return nil, LastError()
 	}
 
-	runtime.SetFinalizer(tree, (*Tree).Free)
-	return tree, nil
+	return allocObject(ptr).(*Tree), nil
 }
 
 func (c *Commit) TreeId() *Oid {

object.go

@@ -0,0 +1,49 @@
+package git
+
+/*
+#cgo pkg-config: libgit2
+#include <git2.h>
+#include <git2/errors.h>
+*/
+import "C"
+import "runtime"
+
+type ObjectType int
+
+var (
+	OBJ_ANY ObjectType = C.GIT_OBJ_ANY
+	OBJ_BAD ObjectType = C.GIT_OBJ_BAD
+	OBJ_COMMIT ObjectType = C.GIT_OBJ_COMMIT
+	OBJ_TREE ObjectType = C.GIT_OBJ_TREE
+	OBJ_BLOB ObjectType = C.GIT_OBJ_BLOB
+	OBJ_TAG ObjectType = C.GIT_OBJ_TAG
+)
+
+type Object interface {
+	Free()
+	Id() *Oid
+	Type() ObjectType
+}
+
+func allocObject(cobj *C.git_object) Object {
+	var object Object
+
+	switch ObjectType(C.git_object_type(cobj)) {
+	case OBJ_COMMIT:
+		object = &Commit{cobj}
+		runtime.SetFinalizer(object, (*Commit).Free)
+
+	case OBJ_TREE:
+		object = &Tree{cobj}
+		runtime.SetFinalizer(object, (*Tree).Free)
+
+	case OBJ_BLOB:
+		object = &Blob{cobj}
+		runtime.SetFinalizer(object, (*Blob).Free)
+
+	default:
+		return nil
+	}
+
+	return object
+}

odb.go

@@ -12,15 +12,6 @@ import (
 	"runtime"
 )
 
-var (
-	OBJ_ANY = C.GIT_OBJ_ANY
-	OBJ_BAD = C.GIT_OBJ_BAD
-	OBJ_COMMIT = C.GIT_OBJ_COMMIT
-	OBJ_TREE = C.GIT_OBJ_TREE
-	OBJ_BLOB = C.GIT_OBJ_BLOB
-	OBJ_TAG = C.GIT_OBJ_TAG
-)
-
 type Odb struct {
 	ptr *C.git_odb
 }

repository.go

@@ -72,35 +72,41 @@ func (v *Repository) Index() (*Index, error) {
 	return newIndexFromC(ptr), nil
 }
 
-func (v *Repository) LookupTree(oid *Oid) (*Tree, error) {
-	tree := new(Tree)
-	ret := C.git_tree_lookup(&tree.ptr, v.ptr, oid.toC())
+func (v *Repository) Lookup(oid *Oid, t ObjectType) (Object, error) {
+	var ptr *C.git_object
+	ret := C.git_object_lookup(&ptr, v.ptr, oid.toC(), C.git_otype(t))
 	if ret < 0 {
 		return nil, LastError()
 	}
 
-	return tree, nil
+	return allocObject(ptr), nil
 }
 
-func (v *Repository) LookupCommit(o *Oid) (*Commit, error) {
-	commit := new(Commit)
-	ecode := C.git_commit_lookup(&commit.ptr, v.ptr, o.toC())
-	if ecode < 0 {
-		return nil, LastError()
+func (v *Repository) LookupTree(oid *Oid) (*Tree, error) {
+	obj, err := v.Lookup(oid, OBJ_TREE)
+	if err != nil {
+		return nil, err
 	}
 
-	return commit, nil
+	return obj.(*Tree), nil
 }
 
-func (v *Repository) LookupBlob(o *Oid) (*Blob, error) {
-	blob := new(Blob)
-	ecode := C.git_blob_lookup(&blob.ptr, v.ptr, o.toC())
-	if ecode < 0 {
-		return nil, LastError()
+func (v *Repository) LookupCommit(oid *Oid) (*Commit, error) {
+	obj, err := v.Lookup(oid, OBJ_COMMIT)
+	if err != nil {
+		return nil, err
 	}
 
-	runtime.SetFinalizer(blob, (*Blob).Free)
-	return blob, nil
+	return obj.(*Commit), nil
+}
+
+func (v *Repository) LookupBlob(oid *Oid) (*Blob, error) {
+	obj, err := v.Lookup(oid, OBJ_BLOB)
+	if err != nil {
+		return nil, err
+	}
+
+	return obj.(*Blob), nil
 }
 
 func (v *Repository) LookupReference(name string) (*Reference, error) {

tree.go

@@ -17,6 +17,19 @@ type Tree struct {
 	ptr *C.git_tree
 }
 
+func (o *Tree) Id() *Oid {
+	return newOidFromC(C.git_tree_id(o.ptr))
+}
+
+func (o *Tree) Type() ObjectType {
+	return OBJ_TREE
+}
+
+func (o *Tree) Free() {
+	runtime.SetFinalizer(o, nil)
+	C.git_tree_free(o.ptr)
+}
+
 type TreeEntry struct {
 	Name string
 	Id  *Oid
@@ -31,22 +44,6 @@ func newTreeEntry(entry *C.git_tree_entry) *TreeEntry {
 	}
 }
 
-func (t *Tree) Free() {
-	runtime.SetFinalizer(t, nil)
-	C.git_tree_free(t.ptr)
-}
-
-func TreeLookup(repo *Repository, oid *Oid) (*Tree, error) {
-	tree := new(Tree)
-	err := C.git_tree_lookup(&tree.ptr, repo.ptr, oid.toC())
-	if err < 0 {
-		return nil, LastError()
-	}
-
-	runtime.SetFinalizer(tree, (*Tree).Free)
-	return tree, nil
-}
-
 func (t *Tree) EntryByName(filename string) *TreeEntry {
 	cname := C.CString(filename)
 	defer C.free(unsafe.Pointer(cname))