i find i have some difficulties to understand this structure.can you help me?Thank you!
struct _DestReceiver
{
 /* Called for each tuple to be output: */
 void  (*receiveTuple) (HeapTuple tuple, TupleDesc typeinfo  DestReceiver *self);// is it a function or others??
 /* Initialization and teardown: */
 void  (*setup) (DestReceiver *self, TupleDesc typeinfo);
 void  (*cleanup) (DestReceiver *self);
 /* Private fields might appear beyond this point... */
};