Re: COMMUTATOR doesn't seem to work

On 12-06-22 11:36 AM, Tom Lane wrote:
> "D'Arcy Cain"<darcy(at)druid(dot)net> writes:
> The thing is that either of those approaches is hugely more expensive
> than just providing a second C function. It costs probably thousands
> of cycles to inline that SQL function, each time it's used in a query.

I assumed itwould be more expensive but didn't know it would be that
much more.

> I doubt that an "auto reverse the arguments" facility would be very
> much cheaper. You could maybe argue that the aggregated maintenance
> and space costs of all the commutator-pair functions are enough to
> justify having some such solution instead, but I'm doubtful --- and
> even if true, getting from here to there would be painful.

And it would only apply to a very specific type of function.

The other idea I had was to just have the second C function call the
first but that didn't work. Here is what I tried.

PG_FUNCTION_INFO_V1(chkpass_eq);
Datum
chkpass_eq(PG_FUNCTION_ARGS)
{
chkpass *a1 = (chkpass *) PG_GETARG_POINTER(0);
text *a2 = (text *) PG_GETARG_TEXT_P(1);
char str[9];

strlcpy(str, a2->vl_dat, sizeof(str));
PG_RETURN_BOOL(strcmp(a1->password, crypt(str, a1->password)) == 0);
}

PG_FUNCTION_INFO_V1(chkpass_eq2);
Datum
chkpass_eq2(PG_FUNCTION_ARGS)
{
return chkpass_eq(PG_GETARG_POINTER(1), PG_GETARG_TEXT_P(0));
}

Now in this specific case the function is trivial and writing it twice
is no big deal but in general I hate writing the same code twice. I
suppose I could extract the actual operation out to a third function
and call it from the others. I may do that anyway just for the value
of the example. Or is there a way to do what I tried above?

--
D'Arcy J.M. Cain <darcy(at)druid(dot)net> | Democracy is three wolves
http://www.druid.net/darcy/ | and a sheep voting on
+1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.
IM: darcy(at)Vex(dot)Net