postgres short uuid custom domain for human management with cast and equality operators

shortid_sid.sql

CREATE DOMAIN public.sid AS CHAR(8);

CREATE OR REPLACE FUNCTION cast_uuid_as_sid(uuid)
    RETURNS sid
    LANGUAGE SQL AS
$$ SELECT substr($1::text,1,8)::sid $$;

CREATE OR REPLACE FUNCTION eq_uuid_sid(id1 uuid, id2 sid)
    RETURNS BOOLEAN
    LANGUAGE SQL AS
$$ SELECT id1::sid = id2  $$;

CREATE OR REPLACE FUNCTION eq_sid_uuid(id2 sid, id1 uuid)
    RETURNS BOOLEAN
    LANGUAGE SQL AS
$$ SELECT id1::sid = id2  $$;

CREATE CAST ( uuid AS sid )
    WITH FUNCTION cast_uuid_as_sid(uuid) AS IMPLICIT;

create operator = (
    leftarg = uuid,
    rightarg = sid,
    procedure = eq_uuid_sid,
    commutator = =);

create operator = (
    leftarg = sid,
    rightarg = uuid,
    procedure = eq_sid_uuid,
    commutator = =);


/*
drop operator = (uuid, sid), = (sid, uuid);
drop cast ( uuid AS sid );
drop function cast_uuid_as_sid, eq_sid_uuid, eq_uuid_sid;
drop domain sid;
 */

select t.id, t.id::sid, t.id = t.id::sid, t.id::sid = t.id
    from (select gen_random_uuid() as id) t