Re: Refactor construct_array() and deconstruct_array() for built-in types

Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> writes:

> On 02.05.22 16:48, Tom Lane wrote:
>> Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> writes:
>>> There are many calls to construct_array() and deconstruct_array() for
>>> built-in types, for example, when dealing with system catalog columns.
>>> These all hardcode the type attributes necessary to pass to these functions.
>>
>>> To simplify this a bit, add construct_array_builtin(),
>>> deconstruct_array_builtin() as wrappers that centralize this hardcoded
>>> knowledge. This simplifies many call sites and reduces the amount of
>>> hardcoded stuff that is spread around.
>>
>>> I also considered having genbki.pl generate lookup tables for these
>>> hardcoded values, similar to schemapg.h, but that ultimately seemed
>>> excessive.
>> +1 --- the added overhead of the switch statements is probably a
>> reasonable price to pay for the notational simplification and
>> bug-proofing.
>> One minor coding gripe is that compilers that don't know that
>> elog(ERROR)
>> doesn't return will certainly generate "use of possibly-uninitialized
>> variable" complaints. Suggest inserting "return NULL;" or similar into
>> the default: cases. I'd also use more specific error wording to help
>> people find where they need to add code when they make use of a new type;
>> maybe like "type %u not supported by construct_array_builtin".
>
> I have pushed this with the improvements you had suggested.

I dind't pay much attention to this thread earlier, but I was struck by
the duplication of the switch statement determining the elemlen,
elembyval, and elemalign values between the construct and deconstruct
functions. How about a common function they can both call? Something
like:

static void builtin_type_details(Oid elemtype,
int *elemlen,
bool *elembyval,
char *elemalign);

- ilmari