reftable: make reftable_record a tagged union

This reduces the amount of glue code, because we don't need a void
pointer or vtable within the structure.

The only snag is that reftable_index_record contain a strbuf, so it
cannot be zero-initialized. To address this, use reftable_new_record()
to return fresh instance, given a record type. Since
reftable_new_record() doesn't cause heap allocation anymore, it should
be balanced with reftable_record_release() rather than
reftable_record_destroy().

Thanks to Peff for the suggestion.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 24 deletions

diff --git a/reftable/record.h b/reftable/record.h
index da75d7d1f1..010a322e90 100644
--- a/reftable/record.h
+++ b/reftable/record.h
@@ -63,16 +63,10 @@ struct reftable_record_vtable {
 	int (*equal)(const void *a, const void *b, int hash_size);
 };
 
-/* record is a generic wrapper for different types of records. */
-struct reftable_record {
-	void *data;
-	struct reftable_record_vtable *ops;
-};
-
 /* returns true for recognized block types. Block start with the block type. */
 int reftable_is_block_type(uint8_t typ);
 
-/* creates a malloced record of the given type. Dispose with record_destroy */
+/* return an initialized record for the given type */
 struct reftable_record reftable_new_record(uint8_t typ);
 
 /* Encode `key` into `dest`. Sets `is_restart` to indicate a restart. Returns
@@ -100,6 +94,22 @@ struct reftable_obj_record {
 	int offset_len;
 };
 
+/* record is a generic wrapper for different types of records. It is normally
+ * created on the stack, or embedded within another struct. If the type is
+ * known, a fresh instance can be initialized explicitly. Otherwise, use
+ * reftable_new_record() to initialize generically (as the index_record is not
+ * valid as 0-initialized structure)
+ */
+struct reftable_record {
+	uint8_t type;
+	union {
+		struct reftable_ref_record ref;
+		struct reftable_log_record log;
+		struct reftable_obj_record obj;
+		struct reftable_index_record idx;
+	} u;
+};
+
 /* see struct record_vtable */
 int reftable_record_equal(struct reftable_record *a, struct reftable_record *b, int hash_size);
 void reftable_record_key(struct reftable_record *rec, struct strbuf *dest);
@@ -114,25 +124,9 @@ int reftable_record_decode(struct reftable_record *rec, struct strbuf key,
 			   int hash_size);
 int reftable_record_is_deletion(struct reftable_record *rec);
 
-/* zeroes out the embedded record */
+/* frees and zeroes out the embedded record */
 void reftable_record_release(struct reftable_record *rec);
 
-/* clear and deallocate embedded record, and zero `rec`. */
-void reftable_record_destroy(struct reftable_record *rec);
-
-/* initialize generic records from concrete records. The generic record should
- * be zeroed out. */
-void reftable_record_from_obj(struct reftable_record *rec,
-			      struct reftable_obj_record *objrec);
-void reftable_record_from_index(struct reftable_record *rec,
-				struct reftable_index_record *idxrec);
-void reftable_record_from_ref(struct reftable_record *rec,
-			      struct reftable_ref_record *refrec);
-void reftable_record_from_log(struct reftable_record *rec,
-			      struct reftable_log_record *logrec);
-struct reftable_ref_record *reftable_record_as_ref(struct reftable_record *ref);
-struct reftable_log_record *reftable_record_as_log(struct reftable_record *ref);
-
 /* for qsort. */
 int reftable_ref_record_compare_name(const void *a, const void *b);