Re: Implicit casts with generic arrays - Mailing list pgsql-hackers

Alvaro Herrera <alvherre@commandprompt.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:bigintsmallintintegeroidrealdouble precisionnumericdatetime without time zonetime with time zonetimestamp
withouttime zonetimestamp with time zoneinterval
 

(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