On 10/17/2013 10:01 AM, Robert Haas wrote:
> But if you're asking my opinion, I think doing it on the function
> level is a whole lot better and easier to get right. A flag like the
> one I mentioned here can be set for one particular function with the
> absolute certainty that behavior will not change for any function with
> some other name. That type of surety is pretty much impossible to get
> with casts.
The other argument for doing it at the function level is that we could
then expose it to users, who could use it to manage their own overloaded
functions. We would NOT want to encourage users to mess with cast
precedence, because it would be impossible for them to achieve their
desired result that way.
On the other hand, prioritization at the function level likely wouldn't
help us with operators at all, because there the cast has to be chosen
before we choose a function. So if we pursued the function route, then
we'd eventually want to add a "preferred" flag for operators too. Which
would be a lot more trouble, because it would affect the planner, but at
least that would be a seperate step.
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com