Add into_{objtype} methods on Object

Similar to the into_object methods elsewhere

src/blob.rs

@@ -87,6 +87,7 @@ mod tests {
         assert!(blob.is_binary());
 
         repo.find_object(id, None).unwrap().as_blob().unwrap();
+        repo.find_object(id, None).unwrap().into_blob().ok().unwrap();
     }
 
     #[test]

src/commit.rs

@@ -334,6 +334,7 @@ mod tests {
         new_head.into_object();
 
         repo.find_object(target, None).unwrap().as_commit().unwrap();
+        repo.find_object(target, None).unwrap().into_commit().ok().unwrap();
     }
 }
 

src/object.rs

@@ -1,5 +1,6 @@
 use std::marker;
 use std::mem;
+use std::ptr;
 
 use {raw, Oid, ObjectType, Error, Buf, Commit, Tag, Blob, Tree, Repository};
 use {Describe, DescribeOptions};
@@ -62,27 +63,55 @@ impl<'repo> Object<'repo> {
         self.cast(ObjectType::Commit)
     }
 
+    /// Attempt to consume this object and return a commit.
+    ///
+    /// Returns `Err(self)` if this object is not actually a commit.
+    pub fn into_commit(self) -> Result<Commit<'repo>, Object<'repo>> {
+        self.cast_into(ObjectType::Commit)
+    }
+
     /// Attempt to view this object as a tag.
     ///
     /// Returns `None` if the object is not actually a tag.
     pub fn as_tag(&self) -> Option<&Tag<'repo>> {
         self.cast(ObjectType::Tag)
     }
 
+    /// Attempt to consume this object and return a tag.
+    ///
+    /// Returns `Err(self)` if this object is not actually a tag.
+    pub fn into_tag(self) -> Result<Tag<'repo>, Object<'repo>> {
+        self.cast_into(ObjectType::Tag)
+    }
+
     /// Attempt to view this object as a tree.
     ///
     /// Returns `None` if the object is not actually a tree.
     pub fn as_tree(&self) -> Option<&Tree<'repo>> {
         self.cast(ObjectType::Tree)
     }
 
+    /// Attempt to consume this object and return a tree.
+    ///
+    /// Returns `Err(self)` if this object is not actually a tree.
+    pub fn into_tree(self) -> Result<Tree<'repo>, Object<'repo>> {
+        self.cast_into(ObjectType::Tree)
+    }
+
     /// Attempt to view this object as a blob.
     ///
     /// Returns `None` if the object is not actually a blob.
     pub fn as_blob(&self) -> Option<&Blob<'repo>> {
         self.cast(ObjectType::Blob)
     }
 
+    /// Attempt to consume this object and return a blob.
+    ///
+    /// Returns `Err(self)` if this object is not actually a blob.
+    pub fn into_blob(self) -> Result<Blob<'repo>, Object<'repo>> {
+        self.cast_into(ObjectType::Blob)
+    }
+
     /// Describes a commit
     ///
     /// Performs a describe operation on this commitish object.
@@ -103,6 +132,19 @@ impl<'repo> Object<'repo> {
             None
         }
     }
+
+    fn cast_into<T>(self, kind: ObjectType) -> Result<T, Object<'repo>> {
+        assert_eq!(mem::size_of_val(&self), mem::size_of::<T>());
+        if self.kind() == Some(kind) {
+            Ok(unsafe {
+                let other = ptr::read(&self as *const _ as *const T);
+                mem::forget(self);
+                other
+            })
+        } else {
+            Err(self)
+        }
+    }
 }
 
 impl<'repo> Clone for Object<'repo> {

src/tag.rs

@@ -150,6 +150,7 @@ mod tests {
         tag.into_object();
 
         repo.find_object(tag_id, None).unwrap().as_tag().unwrap();
+        repo.find_object(tag_id, None).unwrap().into_tag().ok().unwrap();
 
         repo.tag_delete("foo").unwrap();
     }

src/tree.rs

@@ -375,5 +375,6 @@ mod tests {
         tree.into_object();
 
         repo.find_object(commit.tree_id(), None).unwrap().as_tree().unwrap();
+        repo.find_object(commit.tree_id(), None).unwrap().into_tree().ok().unwrap();
     }
 }