"Nikolay Samokhvalov" <pg-bugs(at)samokhvalov(dot)com> writes:
> CREATE CAST (aaa AS text) WITHOUT FUNCTION
> AS IMPLICIT;
> CREATE CAST (text AS aaa) WITHOUT FUNCTION
> AS IMPLICIT;
> trash=# select ('as' || 'df')::aaa;
> aaa
> ------
> asdf
> (1 row)
> In the last case, function aaa_in() wasn't invoked at all and we obtained
> the sting of type aaa with length > 3...
Well, sure. You declared the text to aaa cast as WITHOUT FUNCTION; that
says the system can relabel any legal text value as an aaa. If you want
to enforce a length limit on the cast result, you need to write a cast
function that does it.
regards, tom lane