Maybe it's best to think about this in a capabilities-security aspect. 'o' gives you capabilities to perform 'f'. 'o' can hide its data and only expose functio

Maybe it's best to think about this in a capabilities-security aspect. 'o' gives you capabilities to perform 'f'. 'o' can hide its data and only expose functions that it wishes. With f(o), 'f' needs to be given permission to access 'o' internals.