[GENERAL] how to create a new composite type using already existing composite types

[Iain Barnett]

Hi,

Is there a way to create a new composite type using already existing composite 
type?

For example,

CREATE TABLE inventory_item (
    name            text,
    supplier_id     integer REFERENCES suppliers,
    price           numeric CHECK (price > 0)
);

produces the following type automatically
CREATE TYPE inventory_item AS (
    name            text,
    supplier_id     integer,
    price           numeric
);

but I'd also like to have a type with an extra column for certain functions

CREATE TYPE inventory_item2 AS (
    name            text,
    supplier_id     integer,
    price           numeric,
size    integer
);

but it would be handy if I could reuse inventory_item instead of having to 
retype the whole lot. I can't work out or find the right syntax, can anyone 
show me how? Any help would be much appreciated.

Regards
Iain