Re: SPI API and exceptions

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> SPI was invented before there was proper exception handling, so it
> communicates errors by return values. This makes programming with SPI
> either prone to errors of omission, or very ugly (ultimately, the
> standard reasons why exceptions were invented).

> So I was pondering whether we could introduce exceptions to SPI in some
> way. I'm not sure how. We could invent an entirely separate set of
> functions, or do some tricks in the header that things before
> differently depending on some #define. Any ideas?

For practically all the nontrivial SPI functions, callers already have
to expect that exceptions can be thrown; just not for the specific
error causes called out as SPI return codes. So I wonder whether we
could get away with just converting all the SPI errors to elogs as well.
It would change them from specifically-handled errors into general-case
errors, but for many call sites that's no problem.

Note though that there are some cases where handling of "expected"
errors would get a lot more annoying if we made them into elogs;
for instance SPI_ERROR_NOATTRIBUTE from SPI_fnumber() and friends.
That particular case might be solvable by defining SPI_ERROR_NOATTRIBUTE
as InvalidAttrNumber. I think you'd need to go around and look at all
uses of each SPI_ERROR_XXX code before deciding that it's just dead
weight and should be converted to a generic exception.

regards, tom lane