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Re: Custom type with width specifier

From: Hannu Krosing <hannu(at)tm(dot)ee>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Shachar Shemesh <psql(at)shemesh(dot)biz>,PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Custom type with width specifier
Date: 2004-06-29 10:19:36
Message-ID: 1088504376.2680.4.camel@fuji.krosing.net (view raw or flat)
Thread:
Lists: pgsql-hackers
On P, 2004-06-27 at 17:53, Tom Lane wrote:
> Shachar Shemesh <psql(at)shemesh(dot)biz> writes:
> > What do I need to do in order to get the width specifier into my type? 
> 
> Rewrite the grammar.  Width modifiers are only supported on types that
> are hard-wired into the grammar, mainly because they look way too much
> like function calls to be distinguished without special hacking.
> 
> Consider for example the implications of the fact that this works:
> 
> regression=# select numeric(17,10) '1.23';
>    numeric
> --------------
>  1.2300000000
> (1 row)
>  
> bison has to decide *before scanning beyond the left parenthesis*
> whether "numeric" is a function name or a type name.
> 
> If you can think of a more general solution, I'm all ears, but it looks
> like a hard problem that would require considerable rethinking of the
> present grammar for these things.

can't we make type(width) an actual function which returns another type
?

this would make it even possible to add support for things like
NUMBER(17,10) as an alias for NUMERIC(17,10) as an user-level addon.

---------------
Hannu

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