Using subclass of Range as default return type #559

• asyncpg version: 0.20.1
• PostgreSQL version: 12.1
• Python version: 3.7.7
• Platform: macOS 10.15.4
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes

I created a subclass of the Range type as follows:

from asyncpg.types import Range as Rg

class Range(Rg):
    def issubset(self, other):
        return self._lower >= other._lower and self._upper <= other._upper

    def issuperset(self, other):
        return self._upper >= other._upper and self._lower <= other._lower

    def size(self):
        return self._upper - self._lower

Would it be possible to have this subclass used automatically instead of the default type?

Both set_type_codec and set_builtin_type_codec don't seem to be able to do it.