Re: psql: add \pset true/false

	Jim Nasby wrote:

> I was more thinking it would be nice to be able to temporarily 
> over-ride/wrap what an output function is doing. AFAIK that would allow 
> this to work everywhere (row(), copy, etc). I don't know of any remotely 
> practical way to do that, though.

Yes. Something like:

SET [LOCAL] OUTPUT STYLE FOR  TYPE "typename" TO json_value;

where json_value would represent a set of type-dependant
parameters.
Then the type's output_function and type_modifier_output_function
refered to in CREATE TYPE could use these parameters
to customize the text representation.

For example:
SET output style FOR TYPE bool TO '{"true":"t", "false":"f"}';
or
SET output style FOR TYPE bool TO '{"true":"TRUE", "false":"FALSE"}';

This style declaration doesn't quite fit with GUCs because it should
be bound to a type, but otherwise the behavior is comparable to a
session-wide or transaction-wide SET.

Could be used for date/times too:

SET output style FOR TYPE timestamptz
  TO  '{"format": "DD/MM/YYYY HH24:MI TZ"}';

where applying format would essentially mean
to_char(timestamp, format), which is more flexible
than DateStyle for the output part.


Going even further, maybe some types could support:
SET output style FOR TYPE typename
  TO  '{"function": "funcname"}';

where the function should exist as 
 funcname(typename) returns text
and the type's output_function would just act as a wrapper.

or even:
SET output style FOR TYPE typename
  TO  '{"filter": "funcname"}';
where the function would exist as 
 funcname(text) returns text
and the type's output_function would call funcname
as an output filter for values already in text format.


Best regards,
-- 
Daniel Vérité
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