Sorry,I've misunderstood Thomas's posting.
Please ignore my previous posting.
Hiroshi Inoue
Inoue@tpf.co.jp
> -----Original Message-----
> From: owner-pgsql-hackers@postgreSQL.org
> [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Hiroshi Inoue
> Sent: Friday, July 16, 1999 9:56 AM
> To: Thomas Lockhart
> Cc: Tom Lane; Constantin Teodorescu; Bruce Momjian; Hannu Krosing;
> pgsql-hackers@postgreSQL.org
> Subject: RE: [HACKERS] Interesting behaviour !
>
>
> >
> > > Each type has a typeinput(char * => type ) proc and a typeoutput(
> > > type -> char *) proc.
> > > Doesn't int2in(int4out()) convert int4 to int2 ?
> > > However,typeinput proc causes elog(ERROR) in most cases if it
> > > couldn't convert correctly.
> >
> > Conversion using an intermediate string is possible, but not the
> > preferred technique.
> >
>
> Every type of PostgreSQL must have typeinput/typeoutput procs.
> So this technique doesn't need new procs/operators any more.
> Isn't it an advantage ?
>
> > The "automatic type coersion" code, used earlier in the parser, uses
> > the convention that any single-argument function taking the source
> > type as input and with the same name as the target type can be used
> > for type conversion. For example, the function int4(int2) would
> > convert int2 to int4. There are now routines in the parser for
> > choosing conversion strategies and for finding candidates, and these
> > could be reused for similar purposes when trying to match index
> > arguments.
> >
>
> It seems reasonable.
> But I'm afraid that the defintion of new type requires many functions
> of type conversion.
>
> Regards.
>
> Hiroshi Inoue
> Inoue@tpf.co.jp
>
>