const char *colon = strchrnul(name, ':');
                int refnamelen = colon - name;
 
-               if (!dwim_ref(name, refnamelen, oid.hash, &ref))
+               if (!dwim_ref(name, refnamelen, &oid, &ref))
                        die("no such ref: %.*s", refnamelen, name);
                free(ref);
        }
 
                die(_("Not a valid object name: '%s'."), start_name);
        }
 
-       switch (dwim_ref(start_name, strlen(start_name), oid.hash, &real_ref)) {
+       switch (dwim_ref(start_name, strlen(start_name), &oid, &real_ref)) {
        case 0:
                /* Not branching from any existing branch */
                if (explicit_tracking)
 
                if (e->flags & UNINTERESTING)
                        continue;
 
-               if (dwim_ref(e->name, strlen(e->name), oid.hash, &full_name) != 1)
+               if (dwim_ref(e->name, strlen(e->name), &oid, &full_name) != 1)
                        continue;
 
                if (refspecs) {
 
                return NULL;
        ref = rev->cmdline.rev[positive].name;
        tip_oid = &rev->cmdline.rev[positive].item->oid;
-       if (dwim_ref(ref, strlen(ref), branch_oid.hash, &full_ref) &&
+       if (dwim_ref(ref, strlen(ref), &branch_oid, &full_ref) &&
            skip_prefix(full_ref, "refs/heads/", &v) &&
            !oidcmp(tip_oid, &branch_oid))
                branch = xstrdup(v);
 
        struct commit_list *bases;
        int i, ret = 0;
 
-       switch (dwim_ref(argv[0], strlen(argv[0]), oid.hash, &refname)) {
+       switch (dwim_ref(argv[0], strlen(argv[0]), &oid, &refname)) {
        case 0:
                die("No such ref: '%s'", argv[0]);
        case 1:
 
        if (!remote_head)
                die(_("'%s' does not point to a commit"), remote);
 
-       if (dwim_ref(remote, strlen(remote), branch_head.hash, &found_ref) > 0) {
+       if (dwim_ref(remote, strlen(remote), &branch_head, &found_ref) > 0) {
                if (starts_with(found_ref, "refs/heads/")) {
                        strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
                                    oid_to_hex(&branch_head), remote);
 
                        struct object_id discard;
                        char *full;
 
-                       switch (dwim_ref(name, strlen(name), discard.hash, &full)) {
+                       switch (dwim_ref(name, strlen(name), &discard, &full)) {
                        case 0:
                                /*
                                 * Not found -- not a ref.  We could
 
                        die(Q_("only %d entry can be shown at one time.",
                               "only %d entries can be shown at one time.",
                               MAX_REVS), MAX_REVS);
-               if (!dwim_ref(*av, strlen(*av), oid.hash, &ref))
+               if (!dwim_ref(*av, strlen(*av), &oid, &ref))
                        die(_("no such ref %s"), *av);
 
                /* Has the base been specified? */
 
 
                if (e->item->flags & UNINTERESTING)
                        continue;
-               if (dwim_ref(e->name, strlen(e->name), oid.hash, &ref) != 1)
+               if (dwim_ref(e->name, strlen(e->name), &oid, &ref) != 1)
                        goto skip_write_ref;
                if (read_ref_full(e->name, RESOLVE_REF_READING, &oid, &flag))
                        flag = 0;
 
        return NULL;
 }
 
-int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
+int dwim_ref(const char *str, int len, struct object_id *oid, char **ref)
 {
        char *last_branch = substitute_branch_name(&str, &len);
-       int   refs_found  = expand_ref(str, len, sha1, ref);
+       int   refs_found  = expand_ref(str, len, oid, ref);
        free(last_branch);
        return refs_found;
 }
 
-int expand_ref(const char *str, int len, unsigned char *sha1, char **ref)
+int expand_ref(const char *str, int len, struct object_id *oid, char **ref)
 {
        const char **p, *r;
        int refs_found = 0;
 
        *ref = NULL;
        for (p = ref_rev_parse_rules; *p; p++) {
-               unsigned char sha1_from_ref[20];
-               unsigned char *this_result;
+               struct object_id oid_from_ref;
+               struct object_id *this_result;
                int flag;
 
-               this_result = refs_found ? sha1_from_ref : sha1;
+               this_result = refs_found ? &oid_from_ref : oid;
                strbuf_reset(&fullref);
                strbuf_addf(&fullref, *p, len, str);
                r = resolve_ref_unsafe(fullref.buf, RESOLVE_REF_READING,
-                                      this_result, &flag);
+                                      this_result ? this_result->hash : NULL,
+                                      &flag);
                if (r) {
                        if (!refs_found++)
                                *ref = xstrdup(r);
 
  */
 int refname_match(const char *abbrev_name, const char *full_name);
 
-int expand_ref(const char *str, int len, unsigned char *sha1, char **ref);
-int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref);
+int expand_ref(const char *str, int len, struct object_id *oid, char **ref);
+int dwim_ref(const char *str, int len, struct object_id *oid, char **ref);
 int dwim_log(const char *str, int len, unsigned char *sha1, char **ref);
 
 /*
 
                    strcmp(ret->remote_name, "."))
                        continue;
                if (dwim_ref(ret->merge_name[i], strlen(ret->merge_name[i]),
-                            oid.hash, &ref) == 1)
+                            &oid, &ref) == 1)
                        ret->merge[i]->dst = ref;
                else
                        ret->merge[i]->dst = xstrdup(ret->merge_name[i]);
 
 
        if (len == GIT_SHA1_HEXSZ && !get_oid_hex(str, oid)) {
                if (warn_ambiguous_refs && warn_on_object_refname_ambiguity) {
-                       refs_found = dwim_ref(str, len, tmp_oid.hash, &real_ref);
+                       refs_found = dwim_ref(str, len, &tmp_oid, &real_ref);
                        if (refs_found > 0) {
                                warning(warn_msg, len, str);
                                if (advice_object_name_warning)
 
        if (!len && reflog_len)
                /* allow "@{...}" to mean the current branch reflog */
-               refs_found = dwim_ref("HEAD", 4, oid->hash, &real_ref);
+               refs_found = dwim_ref("HEAD", 4, oid, &real_ref);
        else if (reflog_len)
                refs_found = dwim_log(str, len, oid->hash, &real_ref);
        else
-               refs_found = dwim_ref(str, len, oid->hash, &real_ref);
+               refs_found = dwim_ref(str, len, oid, &real_ref);
 
        if (!refs_found)
                return -1;
 
                if (skip_prefix(line, "deepen-not ", &arg)) {
                        char *ref = NULL;
                        struct object_id oid;
-                       if (expand_ref(arg, strlen(arg), oid.hash, &ref) != 1)
+                       if (expand_ref(arg, strlen(arg), &oid, &ref) != 1)
                                die("git upload-pack: ambiguous deepen-not: %s", line);
                        string_list_append(&deepen_not, ref);
                        free(ref);
 
                return;
        }
 
-       if (dwim_ref(cb.buf.buf, cb.buf.len, oid.hash, &ref) == 1 &&
+       if (dwim_ref(cb.buf.buf, cb.buf.len, &oid, &ref) == 1 &&
            /* sha1 is a commit? match without further lookup */
            (!oidcmp(&cb.noid, &oid) ||
             /* perhaps sha1 is a tag, try to dereference to a commit */