Alls, it's a macro define
#define DECOY(opt, d, ...)+--------------------+
| +-------+ |
| prev | K | V | next|
| +-------+ |
+--------------------+
decoy decoier = DECOY_HEAD;
DECOY(add, decoier);
DECOY(add, decoier);
DECOY(delete, decoier, 10, FALSE);
DECOY(delete, decoier, .key=21, .sort=TRUE);