Shared Constants in PLPGSQL

What's the best way to deal with global constants in PLPGSQL. Currently I
am putting them in a function with out parameters and then calling that
function from every other function that needs them like this.

CREATE OR REPLACE FUNCTION hashids.constants(
OUT min_alphabet_length integer,
OUT sep_div numeric,
OUT guard_div numeric,
OUT default_steps text,
OUT default_alphabet text,
OUT salt text)

I am presuming that if I set this function as immutable the calls to this
function will be cached and will not incur much overhead.

Is there a better way to deal with this?