object.h: add lookup_object_by_type() function

In some cases it's useful for efficiency reasons to get the type of an
object before deciding whether to parse it, but we still want an object
struct. E.g., in reachable.c, bitmaps give us the type, but we just want
to mark flags on each object. Likewise, we may loop over every object
and only parse tags in order to peel them; checking the type first lets
us avoid parsing the non-tags.

But our lookup_blob(), etc, functions make getting an object struct
annoying: we have to call the right function for every type. And we
cannot just use the generic lookup_object(), because it only returns an
already-seen object; it won't allocate a new object struct.

Let's provide a function that dispatches to the correct lookup_*
function based on a run-time type. In fact, reachable.c already has such
a helper, so we'll just make that public.

I did change the return type from "void *" to "struct object *". While
the former is a clever way to avoid casting inside the function, it's
less safe and less informative to people reading the function
declaration.

The next commit will add a new caller.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 18 deletions

diff --git a/reachable.c b/reachable.c
index c598472..84e3d0d 100644
--- a/reachable.c
+++ b/reachable.c
@@ -159,24 +159,6 @@ int add_unseen_recent_objects_to_traversal(struct rev_info *revs,
 				      FOR_EACH_OBJECT_LOCAL_ONLY);
 }
 
-static void *lookup_object_by_type(struct repository *r,
-				   const struct object_id *oid,
-				   enum object_type type)
-{
-	switch (type) {
-	case OBJ_COMMIT:
-		return lookup_commit(r, oid);
-	case OBJ_TREE:
-		return lookup_tree(r, oid);
-	case OBJ_TAG:
-		return lookup_tag(r, oid);
-	case OBJ_BLOB:
-		return lookup_blob(r, oid);
-	default:
-		die("BUG: unknown object type %d", type);
-	}
-}
-
 static int mark_object_seen(const struct object_id *oid,
 			     enum object_type type,
 			     int exclude,