GetAttributeByName

I was wondering if this function should be
'wrapped up' and put into the SPI interface.
I did some research and think I could pull 
it off.

Currently the tutorial uses this:

> bool
> c_overpaid( TUPLE t,             /* the current instance of EMP */
>            int4 limit)
> {
>     bool        isnull = false;
>     int4        salary;
> 
>     salary = (int4) GetAttributeByName(t, "salary", &isnull);
> 
>     if (isnull)
>         return false;
>     return salary > limit;
> }

And the regression test uses this:

> 
> char
> overpaid(tuple)
> TUPLE       tuple;
> {
>     bool        isnull;
>     long        salary;
> 
>     salary = (long) GetAttributeByName(tuple, "salary", &isnull);
>     return salary > 699;
> }


Here is a proposal:

a) An explanation between a TupleTableSlot  and a HeapTuple / TupleDesc pair.  (help?)
  Perhaps we call the (TupleTableSlot *) a  QueryTuple ?  It's called a TUPLE in the  two above usages, where a TUPLE
==(void *)
 

b) Six more functions (overloaded?)
  Existing:
  Datum SPI_getbinval(HeapTuple, TupleDesc, int, bool *)  char *SPI_getvalue (HeapTuple, TupleDesc, int)
  Two more by index:
  Datum SPI_getbinval(TupleTableSlot, int, bool *)  char *SPI_getvalue (TupleTableSlot, int)
  Four more by name:
  Datum SPI_getbinval(HeapTuple, TupleDesc, char *, bool *)  char *SPI_getvalue (HeapTuple, TupleDesc, char *)  Datum
SPI_getbinval(TupleTableSlot,char *, bool *)  char *SPI_getvalue (TupleTableSlot, char *)
 


Hmmm.  Better yet, is there a way to hide 
the difference in the SPI by using a 'smart' 
structure?

Clark