Chapman Flack <chap@anastigmatix.net> writes:
> I wonder if an alternative to making a cast that can't be immutable,
> because it looks at a GUC, could be to offer a choice of cast
> functions: if you need the other behavior, create a schema, do a
> CREATE CAST in it, and put it on your search path ahead of pg_catalog.
Nope, because casts aren't schema-local, since they don't have names.
There can be only one cast between given source and target types.
regards, tom lane