Re: dblink: add polymorphic functions.

Joe Conway <mail@joeconway.com> writes:
> Actually, I had in mind something like:
> 8<---------------------
> int    i;
> int    numargs;
> int   *argtypes;

> numargs = PG_NARGS();
> argtypes = palloc(numargs * sizeof(int));
> for (i = 0; i < numargs; i++)
>     argtypes[i] = get_fn_expr_argtype(fcinfo->flinfo, i);

> if ((numargs == 4 || numargs == 5) &&
>     argtypes[0] == TEXTOID &&
>     argtypes[1] == TEXTOID &&
>     argtypes[2] == INT4OID &&
>     argtypes[3] == BOOLOID)
> {
>     [...]
> }
> else if  ((numargs == 3 || numargs == 4) &&
>     argtypes[0] == TEXTOID &&
>     argtypes[1] == INT4OID &&
>     argtypes[2] == BOOLOID)
> {
>     [...]
> 8<---------------------
> etc.

If the set of allowed argument-type combinations is so easily enumerable,
I don't understand why this is being done at all.  Create a separate SQL
function for each combination.  You can still let the called C functions
call a common implementation routine if that's helpful.

However, this might all be moot in view of Merlin's objection.  It is
definitely completely uncool to have both of these:

>  public | dblink | SETOF anyelement | text, anyelement                | normal
>  public | dblink | SETOF record     | text, boolean                   | normal

It's quite unclear which one will get called for cases like, say, second
argument is a domain over boolean.  And even if the second arg is just a
boolean, maybe the user wanted the first case --- how will he get that
behavior, if so?  These need to have different names, and that might well
help resolve the implementation-level issue...
        regards, tom lane