Re: BUG #12108: Documentation: Limitation of shell types not mentioned

On Mon, Dec  1, 2014 at 12:34:48AM +0000, bouda@edookit.com wrote:
> The following bug has been logged on the website:
>
> Bug reference:      12108
> Logged by:          Ondřej Bouda
> Email address:      bouda@edookit.com
> PostgreSQL version: 9.3.5
> Operating system:   Windows 7
> Description:
>
> According to an older discussion [1], shell types may only be used by
> functions implemented in C. Indeed, in current versions, functions in, e.g.,
> SQL or PL/pgSQL cannot be defined if an argument type or the return type is
> just a shell type.
>
> This is not mentioned in the documentation, however. On the contrary, the
> CREATE TYPE documentation suggests creating a shell type as the "tricky" way
> to define a range type with a canonical function. Neither CREATE FUNCTION
> documentation mentions such a limitation. Thus, when implementing an SQL or
> PL/pgSQL prototype for some new canonical function, one gets stuck on an
> unexpected error.
>
> I suggest mentioning the limitation on the CREATE TYPE page, in the
> paragraph saying how to specify the canonical function.

I have update the docs with the attached patch.  I also noticed that
there is a sentence down at the bottom saying:

    Also, to avoid accidentally cluttering the catalogs with shell types as
    a result of simple typos in function definitions, a shell type will only
    be made this way when the input function is written in C.

I think this explains why only C functions are supported.

Let me know if you have any additional suggestions.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +