Date: Thu, 15 Apr 2021 13:23:13 -0400
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Vik Fearing <vik@postgresfriends.org>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	Robert Haas <robertmhaas@gmail.com>
Subject: Re: Converting contrib SQL functions to new style
Message-ID: <20210415172313.GA9186@alvherre.pgsql>
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On 2021-Apr-15, Vik Fearing wrote:

> CREATE DOMAIN earth AS "$extension".cube.cube
>   CONSTRAINT not_point check("$extension".cube.cube_is_point(value))
>   CONSTRAINT not_3d check("$extension".cube.cube_dim(value <= 3)
>   ...;

I find this syntax pretty weird -- here, the ".cube." part of the
identifier is acting as an argument of sorts for the preceding
$extension thingy.  This looks very surprising.

Something similar to OPERATOR() syntax may be more palatable:

 CREATE DOMAIN earth AS PG_EXTENSION_SCHEMA(cube).cube
   CONSTRAINT not_point check(PG_EXTENSION_SCHEMA(cube).cube_is_point(value))
   CONSTRAINT not_3d check(PG_EXTENSION_SCHEMA(cube).cube_dim(value <= 3)
   ...;

Here, the PG_EXTENSION_SCHEMA() construct expands into the schema of the
given extension.  This looks more natural to me, since the extension
that acts as argument to PG_EXTENSION_SCHEMA() does look like an
argument.

I don't know if the parser would like this, though.

-- 
Álvaro Herrera       Valdivia, Chile