Re: Compatible defaults for LEAD/LAG

Vik Fearing <vik(at)postgresfriends(dot)org> writes:
> On 5/31/20 9:53 PM, Tom Lane wrote:
>> When the anycompatible patch went in, I thought for a little bit about
>> trying to use it with existing built-in functions, but didn't have the
>> time to investigate the issue in detail. I'm not in favor of hacking
>> things one-function-at-a-time here; we should look through the whole
>> library and see what we've got.

> array_replace, lead, and lag are the only functions we have that take
> more than one anyelement.

That's just the tip of the iceberg, though. If you consider all the
old-style polymorphic types, we have

proc
-----------------------------------------------
array_append(anyarray,anyelement)
array_cat(anyarray,anyarray)
array_eq(anyarray,anyarray)
array_ge(anyarray,anyarray)
array_gt(anyarray,anyarray)
array_larger(anyarray,anyarray)
array_le(anyarray,anyarray)
array_lt(anyarray,anyarray)
array_ne(anyarray,anyarray)
array_position(anyarray,anyelement)
array_position(anyarray,anyelement,integer)
array_positions(anyarray,anyelement)
array_prepend(anyelement,anyarray)
array_remove(anyarray,anyelement)
array_replace(anyarray,anyelement,anyelement)
array_smaller(anyarray,anyarray)
arraycontained(anyarray,anyarray)
arraycontains(anyarray,anyarray)
arrayoverlap(anyarray,anyarray)
btarraycmp(anyarray,anyarray)
elem_contained_by_range(anyelement,anyrange)
lag(anyelement,integer,anyelement)
lead(anyelement,integer,anyelement)
range_adjacent(anyrange,anyrange)
range_after(anyrange,anyrange)
range_before(anyrange,anyrange)
range_cmp(anyrange,anyrange)
range_contained_by(anyrange,anyrange)
range_contains(anyrange,anyrange)
range_contains_elem(anyrange,anyelement)
range_eq(anyrange,anyrange)
range_ge(anyrange,anyrange)
range_gist_same(anyrange,anyrange,internal)
range_gt(anyrange,anyrange)
range_intersect(anyrange,anyrange)
range_le(anyrange,anyrange)
range_lt(anyrange,anyrange)
range_merge(anyrange,anyrange)
range_minus(anyrange,anyrange)
range_ne(anyrange,anyrange)
range_overlaps(anyrange,anyrange)
range_overleft(anyrange,anyrange)
range_overright(anyrange,anyrange)
range_union(anyrange,anyrange)
width_bucket(anyelement,anyarray)
(45 rows)

(I ignored anyenum here, since it has no mapping to the anycompatible
family.) Some of these are internal or can otherwise be discounted,
but surely there'd be a market for, say, "int8[] || int4". The big
question that raises is can we do it without creating impossible confusion
with text-style concatenation.

> Are you sure we don't want to give
> at least the anycompatible type a nice public workout with this?

Yes, I'm quite sure. If the idea crashes and burns for some reason,
we'll be glad we didn't buy into it full-speed-ahead right away.

regards, tom lane