select torus(charcol) :: CHAR( ColWidth('public', 'test', 'charcol') ) from test
This throws error in Postgres. ColWidth is immutable and called with constant arguments so it should work. How to fix postgres to allow constant ColWidth() expression in cast ?
ColWidth is NOT IMMUTABLE, your declaration of that property is a lie (the function in your email actually defines it as volatile though...). It is STABLE.
You are basically stuck dealing with this one layer up, outside the server. You would need to execute ColWidth then write the returned value of the function call into the text body of the SQL Command.