Selecting strict, immutable text for a composite type.

[Steven Lembark <lembark@xxxxxxxxxxx>]

Trying to find specific doc's. Lots of people asking similar quesitons
told to work around it different ways. Is there any specific doc on
how to create a default operator class for a given composite type
with any examples of minimal working code to access the pieces and
convert them to text?

I have produced quite a variety of botched syntax on this trying to
see which shit sticks to the wall... just one working example would
be most apprecated.

As an example: Say I wanted to use domains for latitude and longitude
that enforce +/- 180 and +/- 90 and let's say for the moment that
float is an approprite base type (though it might be real or numeric,
that is a seprate question). I can combine the domains into a single
type with a lat and lng elemnt.

So far so good.

Q: What is the syntax for a strict, immutable function in 
   SQL that returns text suitable for use with either 
   creating a "select *" view or a GIST index?

I believe my mistake is somewhere in the number and placement
of paren's but I have tried quite a few combinations based on
various postings without success. Rather than detail them I'm
just asking for a reference to one working example for any
roughly similar composite type.

thanks

Example:

  /*
   * this much works.
   */

  create domain longitude_d
  as
  float
  not null
  check
  (
    VALUE >= -180.0::float
    and
    VALUE <= +180.0::float
  );

  create domain latitude_d
  as
  float
  not null
  check
  (
    value >= -90.0::float
    and
    value <= +90.0::float
  );

  create type lat_lng_t
  as
  (
    lng longitude_d,
    lat latitude_d
  );


  /*
   * someting about this does not work.
   * the signiture seems reasonable,
   * as does the returns ... as.
   *
   * Q: What is the correct syntax for
   *    select ... ?
   */

  create or replace function
  lat_lng_text
  (
    lat_lng_t
  )
  returns text language sql strict immutable as
  $$
    select ($1).lng::text || '-' || ($1).lat::text
  $$




-- 
Steven Lembark                                       1505 National Ave
Workhorse Computing                                 Rockford, IL 61103
lembark@xxxxxxxxxxx                                    +1 888 359 3508