Re: Implicit casts with generic arrays

Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Tom Lane wrote:
>> It looks to me like we could eliminate the conflict if we invented a new
>> polymorphic pseudotype called "anynonarray" or some such, which would
>> act like anyelement *except* it would not match an array.
> ...
> On the contrary, I would think that it fits nicely to "close the loop"
> on the anyarray/anyelement feature set.

OK, I hacked this together and it seems to behave at least as reasonably
as 8.2 does. "8.3" here means HEAD + anynonarray + capturing concat
operators. I used integer as an example of a type for which 8.2 has an
implicit cast to text, and point as an example of a type for which it
doesn't:

Expression 8.3 8.2

text || text text concat text concat
text || 'unknown' text concat text concat
text || text[] array concat array concat
text || non-text array error error
text || non-text scalar text concat text concat [1]

integer || integer error text concat
integer || 'unknown' text concat text concat
integer || integer[] array concat array concat
integer || non-integer array error error
integer || non-integer scalar error text concat [1]

point || point error error
point || 'unknown' text concat 'array value must start ...'
point || point[] array concat array concat
point || non-point array error error
point || non-point scalar error error

text[] || text[] array concat array concat
text[] || 'unknown' error error
text[] || non-text array error error
text[] || non-text scalar error error

[1] for types for which 8.2 has an implicit cast to text, else it fails.
These are:
bigint
smallint
integer
oid
real
double precision
numeric
date
time without time zone
time with time zone
timestamp without time zone
timestamp with time zone
interval

(I was interested to find that there were cases where 8.2 would come out
with the dreaded "array value must start with "{" or dimension
information" error.)

I think that the above chart is pretty defensible; the only cases that
fail now where they worked before are concatenations where neither side
is either text or an unadorned string literal. Frankly, I think this:

catany=# select 3 || 0.4;
ERROR: operator does not exist: integer || numeric

is way preferable to this:

regression=# select 3 || 0.4;
?column?
----------
30.4
(1 row)

which is what 8.2 does --- if you want text concatenation you should
make at least *some* effort to signal that, like casting one side to
text or at least quoting it. Run-together concatenations like

catany=# select 'sin(' || 2 || ')';
?column?
----------
sin(2)
(1 row)

will work as long as at least one of the first two concatenated items is
textual or an unadorned string literal.

Barring objections I'll clean this up and commit it.

regards, tom lane