Re: BUG #1532: typecast problem between arrays of an int8

Tom Lane wrote:
> "Ezequiel Tolnay" <mail@etolnay.com.ar> writes:
>>I've created the cardnumber_t datatype, which is an int8, to provide
>>implicit typecasting with varchar padding the result with zeroes.
>>Conversions work as expected between int4, int8, cardnumber_t and varchar.
>>They also work fine between int4[], int8[] and cardnumber_t[], but when an
>>attempt is made to convert a cardnumber_t[] to a varchar[], the connection
>>is dropped.
>
> What's going on here is that array_map thinks it can use fn_extra of the
> passed FmgrInfo for its own purposes.  That means that if the function
> to be called tries to use fn_extra for *its* own purposes, we have a
> conflict that is going to lead to core dumps in most cases.  In other
> words, array_map pretty much doesn't work for calling anything except
> built-in functions.
>
> I think the best solution to this is to require array_map's caller to
> provide the state storage array_map wants, instead of doing it locally.
> Both of the existing callers can easily incorporate array_map's state
> data into their own state structs.  Joe, you have any better ideas?
>

That certainly looks like the least invasive fix for 8.0.x and 7.4.x.

I have thought before that we were overloading fn_extra a bit too much.
Is there any merit in having more than one "extra" member in FmgrInfo
going forward?

Joe