Re: extensible enum types

Joseph Adams <joeyadams3.14159@gmail.com> writes:
> Couldn't enum_eq just use get_fn_expr_argtype to determine the type of
> enum input rather than rely on it being stored in the value

No.  Support functions have to work in many contexts where there is no
"side channel" such as get_fn_expr_argtype.  What's more, it's very
difficult to provide a side channel without creating security holes.
We used to think it was OK for output functions to rely on a type OID
passed separately from the actual value, but that's insecure:
http://archives.postgresql.org/pgsql-hackers/2005-04/msg00998.php
        regards, tom lane