'Return a :class:`.TypeEngine` object corresponding to a dialect.
This is an end-user override hook that can be used to provide
differing types depending on the given dialect.  It is used
by the :class:`.TypeDecorator` implementation of :meth:`type_engine`
to help determine what type should ultimately be returned
for a given :class:`.TypeDecorator`.
By default returns ``self.impl``.'

def load_dialect_impl(self, dialect):

    return self.impl
