CREATE OR REPLACE FUNCTION avfinal(x anycompatiblearray) RETURNS anycompatiblearray
LANGUAGE plpgsql AS $$
DECLARE
    res real[];
BEGIN
    res := ARRAY_FILL(x[1], ARRAY[4]);
    RETURN res;
END;
$$;

CREATE OR REPLACE FUNCTION acc(x anycompatiblearray, y anycompatiblearray) RETURNS anycompatiblearray
LANGUAGE plpgsql AS $$
BEGIN
    RETURN ARRAY_FILL(y[1], ARRAY[4]);
END;
$$;

CREATE OR REPLACE AGGREGATE public.av(anycompatiblearray) (
    STYPE = anycompatiblearray,
    INITCOND = '{{0},{0}}',
    SFUNC = acc,
    FINALFUNC = avfinal
);

CREATE OR REPLACE FUNCTION aw(real[])
RETURNS void LANGUAGE plpgsql
AS $function$
    begin
    end
$function$;

SELECT 
aw(av(ARRAY[1.0::real])),
aw(av(ARRAY[1.0::real])),
1;