Re: dblink: add polymorphic functions.

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On 07/06/2015 12:39 AM, Michael Paquier wrote:
>> Yeah, particularly the use of first_optarg makes things harder
>> to follow in the code with this patch. A C wrapper has the
>> disadvantage to decentralize the argument checks to many places
>> making the flow harder to follow hence using
>> get_fn_expr_argtype() with PG_NARGS would be the way to go, at
>> least to me. This way, you can easily find how many arguments
>> there are, and which value is assigned to which variable before
>> moving on to the real processing.
>
> Just to be clear I mean that: if (PG_NARGS() == 5) { if
> (get_fn_expr_argtype(fcinfo->flinfo, 1) == TYPEOID) var =
> PG_GETARG_BOOL(1) [...]

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 highest number of arguments is always checked first, the
pattern is not ambiguous even with the extra anyelement.